Doctoral Degrees (Crop Science)

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Aerial phenotyping tp identify superior sugarcane genotypes.
(2024) Hoffman, Natalie.; Joshi, Sheilesh Vinanay.; Singels, Abrahams.
Sugarcane is a globally important food and bioenergy crop which necessitates continual improvement through breeding to ensure its sustainable production under increasingly challenging environments. Compared to other major crops, yield gains in sugarcane have stagnated worldwide in recent years. This could be attributed to the resource-intensive and time-consuming nature of breeding a genetically complex crop with long growth cycles and large, diverse populations. The primary objective of sugarcane breeding is to develop superior genotypes with enhanced genetic gains, securing sustainable production for the future. Aerial phenotyping (AP) with high-throughput phenotyping sensor technologies and unmanned aerial vehicles (UAVs, commonly known as drones) could assist breeding by increasing selection efficiency and accuracy, uncovering genetic variation for yieldpromoting traits, and expediting large-scale trial screening. Key physiological traits governing canopy development and water use, namely green canopy cover (GCC) and stomatal conductance (gs), can be estimated from the aerially measured Normalized Difference Vegetation Index (NDVI) and canopy temperature (Tc), respectively. While promising, further research is required to evaluate the efficacy of AP in breeding. The study aimed to develop and test an AP procedure for identifying superior genotypes in sugarcane breeding. The specific objectives were to: (1) determine the impacts of ground (GCC and gs) and aerially measured traits (NDVI and Tc), on stalk dry mass yield (SDM) under well-watered (WW) and water deficit (WD) conditions; (2) develop an AP procedure for estimating gs, GCC and SDM from Tc and NDVI; (3) determine the genetic variation and broad-sense heritability of ground and aerially measured traits; (4) evaluate the feasibility and potential benefit of implementing AP to identify superior genotypes in breeding. These aims and objectives were addressed in three experimental phases. An unreplicated pilot trial with two genotypes grown under WW and WD conditions (~ 200 m2 in total) was used to establish preliminary relationships between ground and aerially measured traits under varying canopy and moisture conditions. Key findings were that FIPAR (fractional interception of photosynthetically active radiation - a surrogate measure of GCC) measured on the ground could be reliably estimated from NDVI, though the relationship required further investigation at partial canopy cover. Tc could be used to distinguish differences in measured gs between water treatments under moderate to severe stress conditions only. Overall, the experiment was used to formulate a preliminary AP protocol, with recommendations for further improvement in the subsequent phase. A replicated field trial with 54 genotypes, grown under WW and WD conditions (~ 3 ha in total) in plant and first ratoon crops, was used to assess trait correlations, genetic variation and broad-sense heritability of traits, and to refine the AP procedure. In line with previous research, the study confirmed FIPAR and gs as influential traits for determining SDM. FIPAR, measured at 2-3 months after crop start, could be used to identify high- and lowyielding genotypes, and could be predicted well from NDVI, at partial canopy for wellwatered crops. Breeding programs for irrigated environments could benefit from the early identification of superior genotypes if traits with high heritability, like FIPAR, can be accurately and rapidly phenotyped. Furthermore, results suggested that high gs benefits wellwatered crops, while relatively low gs could be advantageous in dry environments, though this requires further validation. Phenotyping of gs from Tc was mostly unreliable, and its practical application in breeding programs requires further evaluation on a larger, genetically diverse population with improved measurement procedures. It was concluded that NDVI and Tc, which both showed significant genotypic variation and moderate to high heritability, could be used to identify high- and low-yielding genotypes when measured early in the crop cycle in young, partially canopied, well-watered crops planted in multi-row plots. Novel results also showed potential for screening of drought tolerance using water treatment differences in Tc and SDM, which has not been reported previously for sugarcane. Overall, this research was used to establish an AP procedure for subsequent use in breeding trials. Lastly, the AP procedure was implemented in two rainfed early-stage breeding trials, with 1770 to 2130 genotypes, planted in replicated single-row plots over ~3.5 – 6 ha. This validation phase was used to test the utility of AP for enhancing selection accuracy and efficiency and contribute to yield improvement. The limited number of flights in the first trial prevented adequate capture of temporal and genotypic variations in aerially measured traits, which are necessary for accurate yield prediction. In the second trial, early estimates of NDVI and Tc, measured approximately 1.5 to 3 months after crop start in partially canopied, well-watered crops, showed significant genotypic variation, moderate to high heritability, and significant correlation with yield. Tc was also significantly correlated with yield when measured shortly after canopy closure but before row overlap due to crop growth. Despite these promising results, the AP procedure implemented in these early-stage breeding trials did not achieve the precision required for genotype selection. A comparison of direct (SDM-based) and indirect (based on aerially measured traits) selection approaches showed that the number of positive matches was mostly offset by a larger number of incorrectly identified genotypes using aerially measured traits. It was concluded that the effectiveness of AP in breeding is currently hindered by limitations in the precision of aerial measurements and challenges in breeding trial execution. The findings from this study highlight the potential and limitations of AP for physiological breeding. AP holds great promise for identifying genetic variation in yield-promoting traits, which could be leveraged in breeding for the identification of superior genotypes in irrigated environments, however further research is required to fully realize this potential. It is recommended to modify the design of early-stage trials by increasing plot length, number of rows, and row-spacing to facilitate accurate estimation of aerially measured traits using the developed AP procedure. Further efforts are also needed to overcome challenges inherent in breeding trial execution, such as lengthy planting periods introducing biases in early vigour, and variability in field soil composition, which directly and indirectly affect the quality of ground and aerially measured data. Should these recommendations be implemented, early screening of trials using AP could lead to shorter breeding cycles, the discovery of novel genetic variations, and improved selection efficiency, ultimately reducing the resourceintensive nature of traditional methods through early elimination of inferior genotypes from the program. In conclusion, this study demonstrates the potential of AP to enhance sugarcane breeding by facilitating the early detection of important yield-promoting traits, particularly in wellwatered crops. While AP shows promise to enhance sugarcane breeding, further work in refining its application is essential to fully realize its benefits. These research findings provide a strong foundation for future efforts to develop innovative breeding strategies and precision agriculture technologies.
Identification of cowpea (vigna unguiculata (L) (walp) genotypes and genetic improvement for enhanced yield and nutritional quality.
(2023) Gumede, Mbali Thembi.; Mabhaudhi, Tafadzwanashe.; Gerrano, Abe Shegro.
Cowpea (Vigna unguiculata (L.) Walp) is a staple legume crop with potential to address food insecurity and malnutrition in the Sub-Saharan Africa (SSA). It is also among the neglected underutilized legume crop species in the region. The crop’s yield production has never met the potential yields of the crop in the SSA. In addition, given its nutritional value, ability to withstand extreme environmental conditions, nitrogen fixation ability and its greater potential to address nutrient deficiencies and food insecurity in the SSA. These attributes make cowpea an ideal crop to sustainable future for the people and environment. There is a need to develop cowpea varieties that are high yielding with high nutritional values to combat food insecurity. Therefore, the objectives of the study were: (1) to assess the genotype by environment interaction effect and select cowpea genotypes with high grain yield and adaptation across selected cowpea growing environments in South Africa, (2) to assess the phenotypic variability and correlation analysis in cowpea based on yield and yield related traits, (3) to evaluate the variations of nutritional content and phytochemical compositions among cowpea genotypes under diverse environments, (4) to assess the genetic diversity among cowpea genotypes using single nucleotide polymorphism (SNP) markers, and to select distinct and complementary genotypes for developing improved cultivars and (5) to determine the combining ability effects and gene action controlling the yield and yield-related traits among selected cowpea parental genotypes and their progenies. The first study assessed the extent of genotype by environment interaction (GEI) of cowpea genotype to the influence of genotype (G), environment (E) and their interaction (GEI) effects on grain yield in cowpea and to assess the stability of cowpea genotypes to identify stable and high-yielding genotypes for broad or narrow adaptation to improve cowpea productivity in South Africa and identify the identical agro-ecologies using analysis of variance (ANOVA), additive main effects and multiplicative interaction (AMMI) and the genotype-by-environment interaction (GGE) biplot analyses. The AMMI ANOVA showed the significant GEI effect which accounted for 57% variation, whereas genotype and environment main effects accounted for 29% and 13% variation, respectively. The AMMI stability values (ASV) analysis identified genotype Acc-Cowp44 as the most stable genotype recording the lowest ASV of 0.03. The biplot depicted eight sectors and environments were clustered into three of the eight sector whereby E4 (Brits 2020/2021), E5 (Loskop 2020/2021), E6 (Mafikeng 2020/2021) and E7 (Polokwane 2020/2021) which formed a mega-environment and the second sector which involved environments E1 (Brits 2019/2020), E2 (Loskop 2019/2020) and E3 (Roodeplaat 2019/2020) formed one mega-environment. The cowpea genotypes Acc-Cowp38, Acc-Cowp2, Acc-Cowp9, Acc-Cowp5 and Acc-Cowp39 were identified as ideal for grain yield, in that order. These genotypes are recommended for production in South Africa or in similar agroecologies, and for incorporation in future breeding programs targeting genetic improvement for grain yield. The second study assessed 50 cowpea genotypes using yield and yield components to determine the phenotypic correlations among them and selection of best performing genotypes among tested genotypes for enhanced cultivar development. The study revealed the significant differences at 5% and 1% level of probability among the assessed grain yield and yield component traits. The study further indicates that number of pods per plant (NPP), pod length (PL), number of seeds per pod (NSP) and hundred seed weight (HSW) had significant and positive correlations with grain yield, therefore these traits can be used as a proxy trait for increased grain yield. Similarly, the principal component analysis (PCA) biplot identified number of branches (NB), number of pods per plant (NPP), pod length (PL), pod width (PW), number of seeds per pod (NSP), and hundred seed weight (HSW) as the important traits in the production of grain yield. Genotypes Acc-Cowp2, 98K_5301, Acc-Cowp4, Acc-Cowp17 and Acc-Cowp9 were grouped together based on their high exhibition of NPP, PW, NSP, PL, HSW and grain yield (GY). The selected genotypes could be considered as potential sources of gene to improve these traits and could serve as parental genotypes in breeding programs targeting enhanced high-yielding varieties. The third study assessed the nutritional and phytochemical traits among the 50 cowpea genotypes to select superior lines with high nutritional compositions for cultivar development for nutritional quality. The study highlighted the significant effects for all nutritional and phytochemical traits for genotype, environment, and genotype by environment interaction evaluated except for flavonoids and fat content. Genotypes Acc-Cowp6, Acc-Cowp17, Acc- Cowp14, 98K_5301, Acc-Cowp9, Acc-Cowp32, Acc-Cowp9, Acc-Cowp4, Acc-Cowp16 and Acc-Cowp21 were selected based on high concentration of Ca, Mg, P, Na and Zn. Genotype Acc-Cowp31 and Acc-Cowp13 were highly associated with protein content while genotype Acc-Cowp39 were in close association with fat content. Further, genotypes Acc-Cowp34, Acc- Cowp18, Acc-Cowp48, Acc-Cowp22, Acc-Cowp26, Acc-Cowp49 and Acc-Cowp28 had low concentrations of total phenolic, flavonoids and condensed tannins. The fourth study used 90 genetically diverse cowpea to assess the magnitude of the genetic diversity and population structure among cowpea genotypes using single nucleotide polymorphisms (SNP) markers. The study revealed that 49% of the selected SNP markers were highly polymorphic and efficiently discriminate the tested cowpea accessions. The low heterozygosity and the high inbreeding coefficients observed among cowpea varieties indicate that the accessions reached an acceptable level of homozygosity. The model-based (structure analysis) and distance-based (UPGM) clustering approaches were used in this study. The model-based analysis revealed the presence of four subpopulations at K = 4 whereas the distance-based cluster analysis classified the cowpea accessions into three distinct clusters. The subpopulations identified exhibited a high level of genetic diversity and were moderately differentiated. This result suggests that the accessions studied are unique and have greater potential to contribute to new varieties for breeding programs in South Africa. The fifth study determined the combining ability effects and gene action controlling the yield and its related traits among 10 selected parental genotypes and 45 crosses using the half diallel mating design. There were significant genotypic, environmental and their interaction effects for almost all traits except leaf length (LL) and number of seeds per pod (NSP) exhibited by both parental genotypes and their progenies. The GCA effects were significant for LW, PL, NSP and HSW whereas the SCA effects were significant for pod width (PW) only. The GCA x environmental interaction effects were highly significant for all traits while the SCA x environmental interaction effects were significant for all the traits except plant height (PH) and LL. The parents Acc-cowp17, Acc-cowp31, Acc-cowp9, Acc-cowp5, Acc-cowp38 and Acccowp19 were identified as good combiners for grain yield and its associated traits productivity. The newly developed progenies Acc-Cowp31 x Acc-Cowp5, Acc-Cowp38 x Acc-Cowp19, Acc-Cowp9 x Acc-Cowp2, Acc-Cowp47 x Acc-Cowp9, Acc-Cowp31 x Acc-Cowp9, Acc- Cowp32 x Acc-Cowp9, Acc-Cowp47 x Acc-Cowp38, and Acc-Cowp17 x Acc-Cowp38 were found to be the best performing due to their desirable SCA effects for enhanced grain yield. The study revealed that trait expression was controlled by both additive and non-additive effect with the additive gene action shown to be the important in controlling traits including NB, LW, NPP, NSP and HSW.
Genetic enhancement of sorghum for yield-related traits and drought tolerance through induced mutagenes.
Wanga, Maliata Athon.; Shimelis, Hussein.
Sorghum (Sorghum bicolor [L.] Moench) is the foundation crop in the world's dry regions, for food, feed, and bioenergy feedstock. There has not been a systematic breeding program and farmers-preferred varieties of the crop in Namibia due to several constraints. There is a need to develop high-yielding and farmer-preferred sorghum varieties with drought-adaptive traits to boost sorghum productivity in the country. The overall goal of this study was to contribute to the national sorghum breeding program aimed at improving sorghum production and productivity through the development and deployment of climate-smart cultivars preferred by farmers and markets in Namibia via induced mutagenesis. The specific objectives of the study were: (1) to assess the present state of sorghum production in northern Namibia and document farmers’ perceived production constraints and trait preferences in new varieties to guide drought-tolerance breeding; (2) to determine the optimum doses of a single and combined use of gamma radiation and ethyl methanesulfonate (EMS) for effective mutation breeding in sorghum; (3) to determine the genetic profile of elite sorghum lines developed via gamma radiation using diagnostic simple sequence repeat (SSR) markers and phenotypic traits for selection; and (4) to determine the Genotype by environment interaction (GEI) of newly-developed mutant and traditional sorghum lines for grain yield and yield related traits for drought-prone areas of Namibia. In the first study, a survey was conducted using a participatory rural appraisal in the following six selected sorghum-growing constituencies: Kapako and Mpungu (Kavango West Region), Eenhana and Endola (Ohangwena Region), and Katima Mulilo Rural and Kongola (Zambezi Region). Data were collected using a structured questionnaire involving 198 farmers in 14 sampled villages across the regions. An equal proportion of male and female respondent farmers cultivate sorghum, suggesting the value of the crop to both genders in Namibia. Most respondent farmers (63.6%) were in productive age groups of <40 years old. In the study areas, low-yielding landrace varieties, namely Ekoko, Okambete, Makonga, Kamburo, Nkutji, Katoma, Fuba, Dommy, Kawumbe, and Okatombo, were widely cultivated, and most of the farmers did not use chemical fertilizers to cultivate sorghum. Farmers’ perceived sorghum production constraints in the study areas included recurrent drought, declining soil fertility, insect pest damage, high cost of production inputs, unavailability of improved seed, lack of alternative improved varieties with farmers’ preferred traits, lack of organic manure, limited access to market and limited extension service. The key farmers’ preferred traits in a new sorghum variety included high grain yield, early maturity, and tolerance to drought and storage pests. The study recommends genetic improvement and new variety deployment of sorghum with the described farmers-preferred traits to increase the sustainable production of the crop in Namibia. In the second study, two concurrent experiments were conducted as follows: in experiment I, the seeds of four sorghum genotypes (Parbhani Moti, Parbhani Shakti, ICSV 15013, and Macia) were treated using five gamma radiation doses (0, 300, 400, 500 and 600 Gray [Gy]), and three EMS doses (0, 0.5 and 1.0%), and gamma radiation followed by EMS (0 and 300 Gy and 0.1% EMS; 400 Gy and 0.05% EMS). In experiment II, the seeds of two sorghum genotypes (Macia and Red sorghum) were treated with only seven doses of gamma radiation (0, 100, 200, 300, 400, 500 and 600 Gy). The combined applied doses of gamma radiation and EMS are not recommended due to poor seedling emergence and seedling survival rate below LD50. The best dosage of gamma radiation for genotypes Red sorghum, Parbhani Moti, Macia, ICSV 15013 and Parbhani Shakti ranged between 392 and 419 Gy, 311 and 354 Gy, 256 and 355 Gy, 273 and 304 Gy, and 266 and 297 Gy, respectively. The optimum dosage ranges of EMS for genotypes Parbhani Shakti, ICSV 15013, Parbhani Moti and Macia were between 0.41% and 0.60%, 0.48% and 0.58%, 0.46% and 0.51%, and 0.36% and 0.45%, respectively. The above dose rates are useful for induced mutagenesis and creating genetic variation in the tested sorghum genotypes for breeding programs. In the third study, 20 mutant lines (which were at mutation generation 7 [M7]) were developed using gamma-irradiation at 350 Gy from the seed of the variety Macia (SDS 3220). Also, five check varieties were used for the comparative study. DNA extraction was carried out on young and fresh leaves samples per test line 20 days after sowing. Seventeen SSR markers amplified a total of 50 alleles, which varied from 2 to 5 (mean = 2.94). The number of effective alleles per locus varied from 1.08 to 2.53, with a mean of 1.96. The observed heterozygosity ranged from 0.00 to 0.21 (mean = 0.09). The mean expected heterozygosity value was 0.45 indicating moderate genetic differentiation of the tested lines for selection and hybridization. Cluster analysis classified the genotypes into three main groups. Moderate to high genetic distance (≥ 0.50) was displayed between drought-tolerant and high-yielding genotypes that aided in selecting mutant lines such as ‘ML2, ML3, ML4, ML7 and ML14’ compared with the check varieties ‘Macia, Kotovara, ICSR 137, and ICSV 17004’. The selected lines are a useful source of genetic variation for breeding high-yielding and drought-tolerant varieties suited for the drought-prone environments of Namibia. In the fourth study, 50 sorghum genotypes, including 10 newly-developed mutant lines (M9), 33 landraces, two sorghum varieties widely grown in Namibia, and five standard check varieties were evaluated under field conditions using a 10 x 5 alpha lattice design with three replications. The experiments were carried out in four environments with two growing seasons in Namibia. Data were collected on grain yield and related traits and subjected to the Additive Main Effects and Multiplicative Interaction (AMMI) model. The AMMI model showed that 93.9% of the total genetic variation was attributed to days to 50% flowering (DF), while 94.04% of the variation was due to plant height (PH), 86.52% to panicle weight (PW), 70.67% to thousand-grain weight (TGW), and 90.68% to grain yield (GY). The larger variations attributed to genotypic effects for PL (36.3%), TGW (33.2%) and PH (20.7%) are useful for genotype selection for yield-related traits. Based on a multi-trait biplot and Best Linear Unbiased Prediction (BLUPs) analyses of the GEI data across all drought-prone testing environments, the medium maturity mutant line designated as L7P9-13 was selected as the best yielding (2 tons/ha) and recommended for the drought-prone areas of Namibia. In summary, the study identified sorghum production systems, key farmers’ perceived production constraints and trait preferences in new varieties in Namibia. Also, the best dosage of gamma radiation and EMS were determined for increasing the genetic diversity in sorghum for genetic enhancement. Newly developed mutant lines ML2, ML3, ML4, ML7 and ML14 displayed moderate to high genetic distance useful for breeding high-yielding and droughttolerant varieties suited for the drought-prone environments of Namibia. The medium maturity and drought-tolerant mutant line designated as L7P9-13 was the best yielding (2 tons/ha) and recommended for large-scale production in the country.
Crop suitability mapping for underutilized crops in South Africa.
(2022) Mugiyo, Hillary.; Mabhaudhi, Tafadzwanashe.; Chimonyo, Vimbayi Grace Petrova.; Kunz, Richard Peter.
Several neglected and underutilised species (NUS) provide solutions to climate change and create a Zero Hunger world, the Sustainable Development Goal 2. However, limited information describing their agronomy, water use, and evaluation of potential growing zones to improve sustainable production has previously been cited as the bottlenecks to their promotion in South Africa's (SA) marginal areas. Therefore, the thesis outlines a series of assessments aimed at fitting NUS in the dryland farming systems of SA. The study successfully mapped current and possible future suitable zones for NUS in South Africa. Initially, the study conducted a scoping review of land suitability methods. After that, South African bioclimatic zones with high rainfall variability and water scarcity were mapped. Using the analytic hierarchy process (AHP), the suitability for selected NUS sorghum (Sorghum bicolor), cowpea (Vigna unguiculata), amaranth and taro (Colocasia esculenta) was mapped. The future growing zones were used using the MaxEnt model. This was only done for KwaZulu Natal. Lastly, the study assessed management strategies such as optimum planting date, plant density, row spacing, and fertiliser inputs for sorghum. The review classified LSA methods reported in articles as traditional (26.6%) and modern (63.4%). Modern approaches, including multicriteria decision-making (MCDM) methods such as AHP (14.9%) and fuzzy methods (12.9%), crop simulation models (9.9%) and machine-learning-related methods (25.7%), are gaining popularity over traditional methods. The review provided the basis and justification for land suitability analysis (LSA) methods to map potential growing zones of NUS. The review concluded that there is no consensus on the most robust method for assessing NUS's current and future suitability. South Africa is a water-scarce country, and rainfall is undoubtedly the dominating factor determining crop production, especially in marginal areas where irrigation facilities are limited for smallholder farmers. Based on these challenges, there is a need to characterise bioclimatic zones in SA that can be qualified under water stress and with high rainfall variation. Mapping high-risk agricultural drought areas were achieved by using the Vegetation Drought Response Index (VegDRI), a hybrid drought index that integrates the Standardized Precipitation Index (SPI), Temperature Condition Index (TCI), and the Vegetation Condition Index (VCI). In NUS production, land use and land classification address questions such as “where”, “why”, and “when” a particular crop is grown within particular agroecology. The study mapped the current and future suitable zones for NUS. The current land suitability assessment was done using Analytic Hierarchy Process (AHP) using multidisciplinary factors, and the future was done through a machine learning model Maxent. The maps developed can contribute to evidence-based and site-specific recommendations for NUS and their mainstreaming. Several NUS are hypothesised to be suitable in dry regions, but the future suitability remains unknown. The future distribution of NUS was modelled based on three representative concentration pathways (RCPs 2.6, 4.5 and 8.5) for the years between 2030 and 2070 using the maximum entropy (MaxEnt) model. The analysis showed a 4.2-25% increase under S1-S3 for sorghum, cowpea, and amaranth growing areas from 2030 to 2070. Across all RCPs, taro is predicted to decrease by 0.3-18 % under S3 from 2050 to 2070 for all three RCPs. Finally, the crop model was used to integrate genotype, environment and management to develop one of the NUS-sorghum production guidelines in KwaZulu-Natal, South Africa. Best sorghum management practices were identified using the Sensitivity Analysis and generalised likelihood uncertainty estimation (GLUE) tools in DSSAT. The best sorghum management is identified by an optimisation procedure that selects the optimum sowing time and planting density-targeting 51,100, 68,200, 102,500, 205,000 and 300 000 plants ha-1 and fertiliser application rate (75 and 100 kg ha-1) with maximum long-term mean yield. The NUS are suitable for drought-prone areas, making them ideal for marginalised farming systems to enhance food and nutrition security.
Assessing variability in yield performance and nutritional quality of citron watermelon (citrullus lanatus var. citroides (L.H. Bailey) mansf. ex greb.) genotypes under drought conditions.
Mandizvo, Takudzwa.; Odindo, Alfred Oduor.; Mashilo, Jacob.
Research is needed to investigate the potential of Neglected Underutilized Crop Species (NUCS) such as citron watermelon, to increase crop diversity and mitigate the effects of prolonged drought because of climate change. Little is known about citron watermelon’s food quality attributes (seed popping yield, nutritional value, and lignin content). In addition, there is a need to understand the agro-morphological, physiological and biochemical characteristics associated with drought tolerance in citron watermelon. Therefore, the objectives of this study were: (1) to assess citron watermelon genotypes for food quality attributes (popping yield, chewability and nutritive value) of seeds based on visual appearance, (2) to screen citron watermelon accessions for drought tolerance using morphological and physiological traits, (3) to study the root system architecture of citron watermelon accessions and identify droughtadaptive root traits for cultivar improvement under water-stressed environments and (4) to reveal how citron watermelon responds to combined stress (water deficit and high temperature) with respect to growth, water status, reserve mobilization and metabolite partitioning at seedling stage. The first study determined whether citron watermelon seed’s nutrient composition and physical properties are related to the visual appearance of seed coat. Brown and red-coloured seeds have a higher popping yield than dark-coloured seeds with poor popping ability and are prone to burning during roasting. Seed coat thickness was closely related to hemicellulose contents and cellulose across all seed coat colours. High hemicellulose, cellulose and lignin contents were found in dark and red seeds associated with thick seed coats and increased chewing strength than white seeds. From a nutritional perspective, dark and red seeds were good sources of Cu, Zn, nitrogen and sulfur than brown seeds. Dark and brown seeds were good Mg sources, whereas dark and red seeds were vital sources of potassium. The second study determined variation in drought tolerance among South African citron watermelon landrace accessions for selection and use as genetic stock for drought-tolerance breeding in this crop and closely related cucurbit crops such as sweet watermelon. The forty citron watermelon accessions evaluated showed varying levels of drought tolerance based on morphological and physiological traits. These allowed five distinct groupings, namely: A (highly drought-tolerant), B (drought-tolerant), C (moderately drought tolerant), D (droughtsensitive) and E (highly drought-sensitive) based on various drought tolerance indices. The following accessions (WWM02, WWM-05, WWM-09, WWM-15, WWM-37(2), WWM-39, WWM-41 (A), WWM-46, WWM-47, WWM-57, WWM-64, WWM-66, WWM-68 and WWM-79) were categorized as highly-drought tolerant and accessions WWM-03, WWM-08, WWM-14, WWM-21, WWM-33, WWM-35(1), WWM-35(2), WWM-67 and WWM-76 as drought tolerant. These are useful genetic stocks for improving drought tolerance in this crop and related cucurbit crops, including sweet watermelon. The third study examined citron watermelon accessions’ root system architecture and identified drought-adaptive root traits for cultivar improvement under water-stressed environments. The study showed that plasticity and biomass allocation shift according to genotype, presumably to optimise the use of limited resources. The study found significant phenotypic variation in root architecture among citron watermelon accessions that may relate to differences in water uptake. The following traits of root system architecture (RSA) (total root length, root system width, convex hull area and total root volume) were associated with drought tolerance. Further, RSA traits such as root dry mass and root shoot mass ratio were highly correlated with root branch count, root system depth, total root length and leaf number. These traits are useful selection criteria for breeding and developing water-efficient citron watermelon accessions for cultivation in drought-prone environments. The fourth study identified multiple abiotic stress-induced modifications in different phytosterols (campesterol, sitosterol and stigmasterol) in the seedling axis (embryonic leaf and root) of genetically distinct citron watermelon accessions. Detailed evaluation of phytosterols was done and the effects of the changes observed in stressed plants were discussed.
Evaluating seed quality and performance of low and high phytic acid maize (Zea mays L.) under varying phosphorus rates and water regimes in dryland conditions.
Bakhite, Mohammed Abdalla Elgorashi.; Odindo, Alfred Oduor.; Magwaza, Lembe Samukelo.
Maize (Zea mays) being the staple crop for many communities in Sub-Saharan Africa and also used for animal feeding, a considerable effort has been made to improve quality and yield. In recent times plant breeders have focused on reducing phytic acid (PA) on maize seeds to improve grain nutritional quality. Although studies of low phytic acid genes have been reported in temperate maize, the current research was based on the tropical genetic background which was screened for low phytic acid. This is the first report for applied breeding of the trait in the tropical maize. Little is known on the agronomy and responses of tropical maize specifically to water stress and its response to phosphorus application. No studies provided on the seed quality performance and response of low phytic acid maize to water stress and phosphorus application. Reducing Phytic acid of tropical maize could have negative effects on seed quality and yield. The primary objective of this study was to compare the performance of low phytic acid (LPA) maize seeds of tropical origin with three other varieties i.e. high phytic acid (HPA) of tropical origin, SC701 and LS8520 based on seed quality and water stress. The study consisted of two maize synthetic populations differing in phytic acid (PA) content (from the African Center of Crop Improvement (ACCI)); namely, LPA and HPA synthetic populations. Both the LPA and HPA synthetic populations were derived from a tropical second generation (F2) population and were selected based on their phytic acid (PA) content. They were produced at the Ukulinga Research Farm, University of KwaZulu-Natal (29°40'05.7"S 30°24'20.9"E), in Pietermaritzburg, South Africa. These two maize synthetic populations were compared with two commercial maize varieties (from McDonald Seeds), white maize (SC701) and yellow maize LS 8520 R (484) which in this study was coded LS8520. All seeds used in this study were produced under identical production conditions and in the same growing season, thereby ensuring that the seeds were of the same physiological age. The first experiment investigated the characterisation of LPA maize varieties for seed germination and vigour. Seed quality was evaluated using the standard germination test and accelerate aging test together with electric conductivity test (EC). The second experiment was conducted as a pot trial to investigate the effect of exogenous phosphorus application on seed quality and yield of low phytic acid maize varieties. In third experiment, a field study over two seasons (2015/2016 and 2016/2017) was conducted at Ukulinga Research Farm in Pietermaritzburg, under dryland conditions. The objective of the experiment was to evaluate the newly produced ACCI’s two genetically synthetic maize populations of LPA and HPA under dryland field condition and compare them with the commercial white and yellow tropical maize varieties their germination, growth, yield and yield components. Lastly, an experiment under controlled conditions on photosynthetic efficiency and yield responses of LPA and HPA maize tropical lines to deficit irrigation. The study was carried out under controlled environment conditions. The objective was to evaluate the photosynthetic efficiency of low phytic acid (LPA) and high phytic acid (HPA) tropical maize varieties grown under water-stressed conditions. The results of the first experiment indicated that the performance of LPA varieties was comparable to those of commercially produced varieties. This study suggests that the combination of LPA lines of tropical origin used in this study was satisfactory to meet the minimum seed quality parameters particularly seed germination and vigour. The results for phosphorus application showed that the application of phosphorus improved the growth, flowering and yield of LPA and other varieties as well. The mean germination time (MGT), germination vigour index (GVI), electrical conductivity (EC) (μS g-1), root length, shoot length and the root-shoot ratio of the harvested seeds after phosphorus application were also improved. When the LPA and HPA tropical maize exposed to dryland environments the results revealed that the SC701 variety outperformed the other three varietiess in growth and yield. It was concluded that the LPA maize performed lower under field conditions. In the water stress trial, results showed that LPA maize varieties recorded higher values of stomatal conductance (gs) and transpiration rate (T) compared to HPA and SC701 for both normal and water stress conditions. HPA showed a significantly (P< 0.001) higher value of photosynthetic rate (A) than LPA and SC701 for all the water stress treatments. HPA and SC701 were comparable in most of chlorophyll fluorescence parameters. With regard to yield, HPA showed increased performance in terms of overall yield and seed weight, and this suggests that HPA varieties are less sensitive to water stress than LPA maize varieties. The results from this study have proven that LPA maize varieties are sensitive to limited conditions and further research under a wide range of environmental conditions is required. Overall, the results indicated that the seed germination of LPA was comparable to other varieties but the yield remains low. There is a need to conduct more experiments to demonstrate the performance of LPA under field conditions in response to phosphorus application and water stress. These differences between the traits could help breed programs. The selection for LPA and HPA tropical maize should be based on their physiological performance to be planted in temperate zones to grant higher yield performance.
Integrated weed management using intercropping and weeding frequency for sorghum, dry bean and cowpea.
(2021) Baker, Conrad.; Nciizah, Adornis Dakarai.; Modi, Albert Thembinkosi.
Weed management is a complex topic in agriculture. This is despite the fact that it may be one of the oldest crop management techniques to improve yield. Currently, agriculture predominantly uses chemical weed control because it produces results quickly, but it has many disadvantages regarding sustainable agriculture. Mechanical weed control also has a high risk regarding the need to mitigate sustainable agriculture challenges from the soil management perspective. Biological weed control is not reliable and could have counterproductive effects. This study aimed to expand the current knowledge about cultural weed control in the context of sustainable integrated weed management practices. Planting highly competitive crop species and manipulation of planting density are among the suggested approaches to cultural weed control. Sorghum (Sorghum bicolor (L.) Moench), dry beans (Phaseolus vulgaris L.), and cowpea (Vigna unguiculata (L.) Walp.) are traditional crops of southern Africa. Small-scale and subsistence farmers continue to rely on these crops as sources of food and fodder. The Agricultural Research Council of South Africa solicited an investigation into intercropping and frequency of weeding culturally in order to produce some indicators to advise small-scale farmers who have no capacity to use the predominant weed control strategies for commercial agriculture. The aim is also to promote sustainable agriculture practices that minimise or avoid use of herbicides. The study was designed to collect relevant data on the response of each one of the three crops to intercropping and cultural weeding frequency. The structure of the thesis is that it has a general review of literature on the topic and a focus on each crop response to the same field trial treatments over two growing seasons is presented in three different chapters. Finally, an integrated analysis of intercropping and weeding frequency interactions is presented in a separate chapter, before the general discussion of all the results are presented as a concluding chapter. Each chapter was written using a format for a separate complete manuscript. Crop growth traits associated with plant height, leaf number, chlorophyll content index, land equivalent ratio (LER), biomass, yield, legume pod production and sweet sorghum Brix value were the major crop performance variables of focus over two growing seasons under sole-cropping, intercropping of all three crops and weeding frequencies. Overall, the study revealed that sweet sorghum benefitted from intercropping with legumes while weeds caused a significant pressure on crop agronomic performance, including land equivalent ratio (LER) and final yield compared with sole cropping. The effect of sweet sorghum on legumes during intercropping is minimised by the earlier legume growth and development to escape competition for light and possibly water and nutrients, respectively. It is generally recommended that reduction of weeding frequency may have less effect on sorghum yield in an intercropping system with dry beans or cowpeas. The principal component analysis (PCA) evaluation allowed the study to identify the predominant weed species based on the relative importance value (RIV%). Although this finding cannot be used to associate the weed species with the cultural weed management approach used in this study, it is a significant guideline for predicting weed occurrence, especially in the context of providing extension advice to small-scale farmers. Keywords: beans; cowpeas; cultural weed management; intercropping; sorghum; yield; weeding frequency
Role of fertilisation regimes on the yield and nutritional benefiits of cowpeaamaranth intercropping systems.
(2020) Mndzebele, Buhlebelive Melusi Mgcini Phiwayinkosi.; Modi, Albert Thembinkosi.; Mabhaudhi, Tafadzwanashe.; Ncube, Bhekumthetho.
Several African leafy vegetables (ALVs) contribute to food and nutritional security of rural communities, particularly due to their ability to grow in marginal soils. These ALVs such as amaranth and cowpea among others provide valuable macro- and micronutrients that are key to rural household dietary needs. The aim of this study was to assess the effect of fertiliser application on the symbiotic nitrogen fixation, enzymatic phosphatase activity, agro biological properties, nutrition as well as recommended daily allowance in an intercropped Amaranthus cruentus (amaranth) and Vigna unguiculata (cowpea) farming system. The nitrogen fixation and nutritional yield of cowpea-amaranth intercrop study was motivated by limited information relating symbiotic nitrogen fixation and fertilisation of ALVs, such as cowpea and amaranth grown under intercropping system, in addition to nutritional yield. Field trials were conducted at the Agricultural Research Council (ARC), Vegetables and Ornamental Plants campus situated in Roodeplaat, Pretoria, South Africa, during 2014/15 and 2015/16 summer seasons from November to January. The 2 x 4 factorial experiments were laid out in a completely randomized design (CRD) with four replications. The factors evaluated were intercropping (amaranth and cowpea) and fertiliser (control, 25%, 50%, and 100% of the recommended NPK levels). Soil sampling was done before land preparation and soil nutrient analysis was done at the Agricultural Research Council–Soil, Climate and Water (ARC–SCW). The application of nitrogen, phosphorus and potassium were guided by the soil analyses results and recommendations on both seasons. Vigna unguiculata was sown directly in the soils and amaranth was transplanted approximately four weeks after planting amaranth in the nursery. Irrigation was done based on reference evapotranspiration (ET) and a crop factor for each crop. Collected data included acid and alkaline phosphatase activity, phosphorus in the soils, phosphorus in the cowpea and amaranth plants, as well as biomass of cowpea and amaranth at physiological maturity. In the rhizosphere of cowpea and amaranth grown as sole crops, there was a higher acid and alkaline phosphatase activity as compared to those on intercropping. The highest rhizospheric phosphatase activity occurred when both crops were grown without fertilizer or 25% NPK. Applying NPK activates soil-bound phosphorus (P) using root exudates, which is important for the production of ALVs. The results showed a reduction in symbiotic N2 fixation of cowpea with the increase fertiliser addition. The above ground and above ground edible biomass of amaranth increased proportionately to the rate of fertiliser application up to 100% NPK, but in cowpea it only increased up to 50% NPK. Nutritional yield of iron and zinc increased with the increase in fertiliser application amounts on cowpea and amaranth. The land utilisation values were greater than one, hence an advantage of intercropping. Cowpea was more aggressive, showed high actual yield losses and high competitive ratio relative to amaranth. More income could be obtained from intercropping cowpea and amaranth compared to the respective sole crops at 100% NPK. In the experiment on the potential of intercropped amaranth and cowpea to meet nutritional requirements, the seasonal above ground and above ground edible biomass of amaranth and cowpea increased with fertiliser application up to 100% NPK. More above ground and above ground edible biomass on amaranth and cowpea were obtained in sole cropping when compared to intercropping. Macro and trace nutritional element contents were highest at 100% NPK fertiliser level. The lowest nutritional contents of macro and trace elements was recorded at the control. Overall, amaranth and cowpea contributed to the recommended daily allowance of calcium, magnesium, iron, and zinc, where there was more at the 100% NPK fertiliser level. The research demonstrates the benefits of grain leguminous crops in soil nutrient fertility enhancement and inorganic fertilization with intercropping in managing micronutrient deficiency to meet the nutritional needs of rural communities. Moreover, the study demonstrated the benefit of applying 25%NPK to 50%NPK fertiliser on the above ground and above ground edible biomass of amaranth and cowpea. In sum, macro and trace elements that are crucial for the nutritional health of rural communities were improved, thus contributing more to the recommended daily allowance, which limits food and nutrition insecurity, and fosters sustainable development.
Physiological analysis of responses of lateral branching of the primary root for tolerance to phosphorus stress and drought in the common bean (Phaseolus vulgaris L.).
(2021) Camilo, Samuel Alves.; Sibiya, Julia.; Odindo, Alfred Oduor.
Common bean (Phaseolus vulgaris L.) is essential to the food security of millions of people in developing nations. However, inadequate precipitation and low soil fertility, mainly phosphorus (P) deficiency, tend to limit its production in smallholder systems. Drought stress severely restricts root growth, binding the capacity of soil water exploration in deep horizons, while phosphorus (P) limitation increases the root capacity of foraging for nutrients in the top soil. Therefore, the development of traits associated with drought resistance and phosphorus stress will contribute to common bean improvement for lines suited for these environments. Thus, the present study aimed to evaluate the physiological response of lateral branching of the primary roots for tolerance to low phosphorus and drought stress in the common bean. To achieve this, pot and field experiments were established at the Agricultural Research Institute of Mozambique (IIAM) - Chókwè Research Station to: (1) determine the effect of drought stress on crop performance at different bean growth stages in the field and pot trials, (2) evaluate phosphorus use efficiency on grain yield efficiency index (GYEI) and P concentration in the plant tissues of selected genotypes in a pot study, and (3) assess the contribution of root phenes to shoot biomass and grain yield under combined stress (drought and low P) in the field and pot study. Eight genotypes were tested for shoot biomass, root biomass, shoot P concentration and uptake assessment in the pot study. For the field experiments, a total of 24 bean lines were used to assess phenology, yield components and total yield per unit. All pot studies were set using a randomized complete block design in a factorial arrangement with four replications. The first study had two levels of water (water stress and irrigated- no water stress); while the second study had two treatments combining phosphorus levels x genotypes, grown in a system of stratified phosphorus, 0.025 g P kg−1of soil as low rate and 0.2 g P kg−1 of soil as high P rate. The last pot experiment combined both water and phosphorus levels and, in all cases, eight genotypes were tested. The field experiment was set as a split plot design with four replications for the drought and phosphorus studies, while for the combined study it was set as a splitsplit plot. Water stress lowered substantially the leaf relative water content, leaf water potential and all growth parameters in the pot experiment, decreasing shoot biomass by 47%, leaflet growth rates by 49% and number of leaflets by 53%. In spite of significant reduction, these variables were highly and positively correlated, and can be recommended for early selection of genotypes grown under limited water conditions. Phosphorus levels also significantly affected shoot and root biomass, shoot phosphorus concentration, phosphorus uptake and phosphorus leachate under high P levels. However, genotypes responded differently to phosphorus levels in term of root biomass, shoot biomass and P uptake; genotypes BFS 81, SEQ342-87 and IBC 301-204 performing better in terms of root and shoot biomass as well as P uptake. These genotypes can be recommended for early selection under low soil fertility, especially in soils with P deficiency. Under field conditions, drought stress had a significant effect (p<0.05) on yield components. Among all the genotypes evaluated, SEF 16, SX 14825- 7-1, TARS MST-1, SEN 52, BRT103- 182, FBN1211-66, IBC 301-204, SER 125 and MHR 311-17 were the most adapted and showed the best yield performances under drought stress, and therefore can be incorporated in breeding programs particularly in drought prone areas. Meanwhile, high phosphorus treatment significantly increased all yield components (pods per plant, 100- seed weight, and grain yield), and variability among genotypes was also observed for yield and yield components. Based on the grain yield efficiency index (GYEI), 10 bean lines out of the 24 were categorized as P use efficient genotypes and therefore, they can be used in phosphorus deficient soils as well as crop improvement program. Grain yield from field data under drought stress and low P were positively correlated with the pot data on root traits. Response of root phene to drought and phosphorus stress appeared to be related to the phenotype traits of water stress and P use efficiency (that is, deep and shallow rooted systems, respectively). Deeper rooted genotypes produced more total root biomass, high taproot lateral branching density, which resulted in high total root length under drought and low P stress. On the other hand, shallow rooted genotypes allocated relatively low total root biomass and less allocation of taproot lateral branching. Increase in shoot biomass and seed yield in drought and low P stress was associated with higher mean values of taproot lateral branching density and total taproot length. Genotypes SER 125, BFS 81, FBN12111-66 and MER 22 11-28 showed greater score of taproots branching density in the pot study with the highest grain yield in the field under low P and drought stress. Therefore, these genotypes can be used in phosphorus deficient soils and drought stress environments or serve as parents for improving phosphorus use efficiency and drought tolerance in common bean. An increased total taproot lateral branching and length observed under stressful conditions (drought stress), contributed for plant performance, and could be considered as an important trait for selecting cultivars. Although no previous study has explicitly explored the utility of taproot lateral length and lateral branching for plant performance under edaphic stress, results from the present study suggest that an increased taproot lateral branching and length provide benefits under multiple environments. Genotypes that exhibited higher scores of taproot lateral branching in the field such as SER 125, BFS 81, FBN12111- 66 and MER 22 11-28, combining with higher grain yield under low P and drought were ranked as deeper rooted and suited to environments where water is limiting. In contrast, genotypes INB 814, SEN52, BIOF 2-06 and SEQ342-87 had relatively low scores of tap root branching density, but with better yield under low P and drought, and were classified as shallow rooted and suited to environments where P is limiting. Keywords: common bean, taproot lateral branching, drought, phosphorus use efficient
Agro-morphological, nutritional and genetic diversity analyses of Bambara groundnut (vigna subterranea (L.) Verdc)
Hlanga, Nokuthula Cherry.; Modi, Albert Thembinkosi.
Bambara groundnut (Vigna subterranea (L.) Verdc) is a legume crop with potential to address food insecurity in sub-Sahara Africa. However, a lack of agronomic, genetic and nutritional information on the crop hinders its full potential utilization. Nineteen Bambara groundnut lines were evaluated in the field in 2017 and 2018 at two sites. The lines showed significant differences (P<0.05) for all the measured traits. Lines such as IITA686, Cream and Uniswa Red-R were found to have superior performance for multiple traits such as number of seeds per plant, seed mass per plant, plant height and mid-leaf width. The genetic variation among the Bambara groundnut lines was assessed using 20 polymorphic SSR markers The markers exhibited an average polymorphic information content (PIC) of 0.57 and the observed heterozygosity was 0.58, showing that the lines exhibited a considerable level of outcrossing. The lines were clustered into three groups based on the principal coordinate analysis. The highest genetic distance was 0.60 between Tiganecuru and S19. Lines such as IITA686, Cream and Uniswa Red-R that had good performance for multiple agronomic traits occurred within a genetic distance of 0.40 making them genetically divergent enough for generating crosses for Bambara groundnut improvement. The ash, fat, proteins, starch, calcium (Ca), iron (Fe), potassium (K), magnesium (Mg), manganese (Mn), phosphorous (P), sodium (Na), copper (Cu), and zinc (Zn), acid detergent fiber (ADF) and neutral detergent fiber (NDF) contents were determined in the Bambara groundnut lines using combustion and chemical digestion procedures. The nutritional content varied significantly (p<0.05) among the lines with lines S19, Gresik, Pong-Br-UNK, Pong-Cr exhibiting high means for starch and protein content ranging from 11.05 to 11.94%. Genotypes Mix, Pong-Br-UNK, 42-1, Gresik, Uniswa Red-R, and Brown were clustered together based on their high starch, Na, Ca, fat, and Mn contents. The negative correlations among some of the nutritional content would be a challenge for simultaneous selection to breed nutritious Bambara groundnut lines. The lines with high content for multiple nutritional elements such as 211-57, Pong- Br-EN and Uniswa Red-G were recommended for production. It was imperative to determine interrelations among agronomic traits and nutritional content with seed mass for indirect selection. Among the agronomic traits, number of seeds (NS r=0.58, p<0.01), number of healthy seeds (NHS, r=0.51, p<0.05) and plant height (PH, r=0.45, p<0.05) exhibited the strongest associations with seed mass. These traits had NS, NHS and PH high direct effects on seed mass of 2.04, 1.72 and 0.60, respectively. These findings provide a means to facilitate indirect selection of genotypes with high seed mass productivity via proxy. Overall, the study found significant agro-morphological and genetic variation among the Bambara groundnut lines, which would be a prerequisite for Bambara groundnut improvement. The superior lines identified for multiple traits and genetic divergence were IITA686, Cream and Uniswa Red-R. Key words: Agro-morphology; Bambara groundnut; Genetic variation; Seed quality
Farmer perceptions and the agronomic potential of provitamin A-biofortified maize on small holder farming systems of KwaZulu-Natal, South Africa
(2019) Zuma, Mthokozisi Kwazi.; Modi, Albert Thembinkosi.; Kolanisi, Unathi.
Pro-vitamin A biofortified maize (PVABM) has the potential to reduce Vitamin A deficiency (VAD) for the vulnerable groups of Sub Saharan Africa (SSA). It is therefore important to understand the willingness of farmers to incorporate PVABM into their farming systems and the agronomic potential of these varieties under different environmental conditions to motivate their introduction in smallholder farming systems. The objectives of the study were to (i) determine smallholder farmer perception of the incorporation of PVABM in in two distinctly different climatic regions of KwaZulu-Natal, South Africa, (ii) evaluate production potential and selected seed quality characteristics of PVABM compared with common maize varieties across two seasons (2015/16 and 2016/17) and (iii) access the potential acceptability of PVABM as part of traditional household diet by smallholder farmers. Results showed that farmers have positive perceptions of the incorporation of PVABM into their farming systems and there was a willingness to adopt these varieties. With respect to seed quality, although there were no significant pro-germination characteristics as determined by tetrazolium test for metabolic activity, PVABM showed better germination vigour index and final germination. Germination performance was significantly correlated with crop establishment during field trials over both seasons. This was shown by highly significant differences observed for plant growth and chlorophyll content index in both study areas across two seasons. However, the study showed no significant differences in biomass and grain yield. Sensory evaluation showed that PVABM traditional foods (green mealies and cooked maize meal) were accepted for consumption and the farmers expressed the willingness to consume PVABM in their diets. The study indicated that PVABM can be accepted by farmers into farming systems. It is recommended that plant breeding to identify genetic differences and potential to improve PVABM for a wide range of agro-ecological conditions in regions where poor smallholder farmers grow maize is performed with a view to improve food security.
Crop fertigation (nitrogen and phosphorus) with decentralised wastewater treatrment system effluents and effects on soil and groundwater.
(2018) Musazura, William.; Odindo, Alfred Oduor.; Buckley, Christopher Andrew.; Hughes, Jeffrey Charles.; Tesfamariam, Eyob Habte.
Urbanisation is contributing to increased informal settlements in peri-urban areas and municipalities are facing challenges in providing sanitation. The decentralised wastewater treatment system (DEWATS) is a low cost, water-borne, onsite sanitation technology that can potentially serve peri-urban areas. The DEWATS treats human excreta to produce effluent that contains mineral nutrients, especially nitrogen (N) and phosphorus (P). Discharging treated wastewater into water bodies may cause pollution. Considering water scarcity, poverty and hunger issues in most developing countries, reuse of treated wastewater in agriculture promotes sustainable development if done in an environmentally friendly manner. This study therefore aimed at understanding the effects on crops, soils and the environment of fertigating with DEWATS effluent. All the studies were conducted at Newlands-Mashu experimental site (30°57’E, 29°58'S), Durban, South Africa. A field experiment investigated the effects of DEWATS effluent on tissue cultured banana (Musa paradisiaca var Williams) and taro (Caucasia esculenta). The study was carried out in a randomised complete block design with two irrigation treatments (DEWATS effluent without fertiliser vs tap water + fertiliser). Two crops were grown in an intercrop over two cropping cycles using drip irrigation. Two sources of effluent from the DEWATS were used. Effluent after treatment through a horizontal flow constructed wetland (HFCW) was used during the first cropping cycle and anaerobic filter effluent (AF) was used in the second cropping cycle. Data was collected on soil leachates, soil chemical properties, water table level, crop growth, yield and nutrient uptake, with a focus on N and P. Fertigation with DEWATS significantly (p < 0.05) increased taro growth during the first cropping cycle. No significant differences (p > 0.05) were reported for crop yield, N and P uptake and leaching between treatments showing its potential to substitute for inorganic fertilisers. The AF effluent significantly (p > 0.05) increased soil inorganic N in the 0.3 m soil depth (rooting zone) after the second cropping cycle thereby acting as important N fertiliser source. Based on the findings no water table hazards due to low deep percolation and subsurface lateral flow was detected. However, subsurface drainage must be constructed in areas where water table rises to prevent groundwater pollution. A pot experiment was conducted to investigate fertigation of banana using DEWATS effluent on three different soil types. A factorial study was conducted in a complete randomised design. The treatments were three soil types (Inanda (Ia); Rhodic Hapludox / acidic clay soil, Sepane (Se); Aquic Haplustalf / clay loam soil and Cartref (Cf); Typic Haplaquept / sandy loam soil) * two irrigation sources (DEWATS effluent vs tap water + fertiliser) * four replicates. The Ia soil was collected from Worlds View, Pietermaritzburg (29°35′S, 30°19′E), the Cf soil from KwaDinabakubo, Hillcrest (29°44’S; 30°51’E) and the Se was from the field trial site at Newlands-Mashu. Soils for the tap water + fertiliser treatment were mixed with inorganic fertilisers based on recommended crop requirements before being packed in a 90 L pot. The study was carried out over 728 days and all soils were irrigated to field capacity. Data was collected on banana growth (total leaf area and plant height), yield, N and P uptake and leaching, and soil chemical properties. Use of DEWATS effluent significantly (p < 0.05) increased banana growth and yield in the Cf soil thereby showing ability of effluent to improve productivity in nutrient deprived soils. The NH4+-N and P concentrations significantly increased in all DEWATS effluent fertigated soils. Therefore, the effluent is a source of fertiliser that can potentially be used in place of conventional inorganic fertilisers. The N leached from the DEWATS treatment was significantly (p < 0.05) lower than from the tap water + fertiliser treatment hence its use is environmentally sustainable. In all soils fertigated with DEWATS effluent, N leaching was significantly high in Ia soil hence fertigation in such a soil needs proper scheduling. The soil water balance (SWB-Sci) model was used to simulate water, and N and P dynamics in DEWATS effluent fertigated soil. The model was calibrated and validated based on data collected in the field studies. The crop growth model was successfully validated as it met all the standard statistical criteria required (i.e. r2 > 0.8, MAE < 20 % and D > 0.8). High concentrations of inorganic N and P in topsoil fertigated with DEWATS effluent were simulated. Nitrate leaching was comparably higher in DEWATS effluent fertigated soils but without significant impact on ground water contamination in the respective soil. Therefore, the use of DEWATS effluent in clay soils is sustainable. The calculated land area required to fertigate banana and taro in an intercrop using effluent from each DEWATS was 117 m2·household-1 (23.3 m2·person-1). If banana is grown as a sole crop land requirement could have been Cf (290 m2 household-1; 58 m2 person-1), Ia (260 m2 household-1; 52 m2 person-1) and Se (200 m2household-1; 40 m2 person). Based on these findings it can be concluded that DEWATS effluent increases crop growth, yield, nutrient uptake and soil inorganic N and P within the rooting zone like more conventional practices. On-farm irrigation management practices such as scheduling with room for rainfall helps to prevent N and P leaching and rising water table. The SWB-Sci model is an irrigation scheduling and nutrient (N and P) management tool which may be used by decision makers and local governments in producing practical guidelines for sustainable wastewater use projects.
Conceptual conservation agriculture adoption in Zimbabwe.
(2018) Mugandani, Raymond.; Mafongoya, Paramu L.
The adoption of conservation agriculture is increasingly becoming important in southern Africa to sustainably increase food security, manage degraded lands and increasing resilience of agricultural systems to climate change. The practices is relevant to the smallholder farming systems of Zimbabwe where productivity is constrained by lack of access to agricultural inputs, decline in soil fertility and increasing rainfall variability. However despite years of research and extension, the adoption of the practice is very limited and piecemeal in Zimbabwe. Therefore, the main objective of the research was to get an in depth understanding of the barriers to adoption of conservation agriculture in Zimbabwe with specific reference to smallholder farmers. The study employed participatory approaches to collect data in Chivi, Murehwa and Mutoko districts. A pre - tested questionnaire was administered to three selected wards in each of the three district. The questionnaire was triangulated through focus group discussions, key informant interviews and personal observations in order to enhance the richness of our findings. Household survey data was analysed using Statistical Packages for Social Scientists and Statistical Analysis Software, while information obtained during key informant interviews and focus discussions was analysed through thematic analysis. Our results revealed that despite agriculture contributing to the livelihoods of the majority of the smallholder farmers, less than 10 % of the respondents had any formal agricultural training. On the other hand, the level of knowledge on conservation agriculture was high amongst the respondents. However, the non - adopters had an indifferent perception about the technology. The significant (P < 0.05) explanatory variables of the knowledge attribute were age, gender, education, visit to demonstration centres and years of practicing the technology, while the perception attribute was explained by age, gender, education, visit to demo sites, experience in conservation agriculture and agriculture. On the other hand, we found a weak but significant correlation between knowledge and perception (Rs = 0.36, P < 0.05), knowledge and adoption (Rs = 0.484, P < 0.05) but strong and significant correlation between perception and adoption (Rs = 0.808, P < 0.05). The later points to a very important point, that adoption of conservation agriculture can be improved by increasing positive perception of the farmers towards the technology. We also found out that the respondents adopted conservation agriculture through the knowledge (mean score of 2.13; standard error = 0.043)) and compliance (mean score of 2.02; standard error = 0.043) pathways. The explanatory variables of the knowledge pathway were education, experience in agriculture, agricultural training and visit to demonstration centers while the gender of the household was the significant variable in explaining the compliance pathway. The study also investigated access to equipment by smallholder farmers. The results indicate that the respondents had low access to conservation agriculture equipment (mean score of 1.72). The respondents indicated that availability, affordability accessibility and acceptability were the main non - socio - economic constraints to accessing conservation agriculture equipment. On access to agricultural markets, we found out that farmers had low level of access to markets (mean score of 1.814). Gender of household head (β = - 1.3196) and age of household head (β = - 0.63198) all had inverse but significant relationship with access to agricultural markets by the farmers. However, access to inputs (β = 2.3893), access to extension (β = 1.21) and belonging to agricultural groups (β = 0.887) all had positive and significant relationship with access to agricultural markets by the smallholder farmers. The study recommends closing negative perception gaps, understanding appropriate adoption pathways in the promotion of conservation agriculture and providing guidelines on “true” conservation agriculture, linking farmers to markets and improved access to conservation agriculture equipment as the main drivers of adoption of the technology among smallholder farmers in Zimbabwe.
Effects of biochar addition on soil nitrogen retention and vegetable uptake in intensive production systems, China.
(2017) Yu, Ying Liang.; Odindo, Alfred Oduor.; Pillay, Balakrishna.; Yang, Linzhang.
China has a limited area of cultivated land per capita and an increasing population. Maintaining a high crop yield is essential to meet the large food demand and to assure grain self-sufficiency. With the pace of economic development, the demand for vegetables keeps growing. In Southern China, many of the fields used to grow vegetables were previously under paddy production. Compared to the paddy production system, the vegetable production system is intensive with excessive use of nitrogen fertilizer. Excessive nitrogen fertilizer application has changed soil chemical properties and nutrient dynamics, and thus created a negative impact on sustainable agricultural development. A preliminary study was conducted in the absence of nitrogen fertilizer to determine the effect of field utilization conversion on soil nitrogen uptake by pakchoi. It was found that soil pH values and organic matter content decreased with intensive vegetable planting and nitrogen leaching loss was higher from vegetable soils compared to that from paddy soils. Although the soil mineral nitrogen content in vegetable soils was higher than that in paddy soils, nitrogen uptake by plants from vegetable soils was lower than that from paddy soils, and decreased quickly in the later growing seasons. The lower plant nitrogen uptake was attributed to the high nitrogen leaching loss and soil acidity caused by the excessive application of nitrogen fertilizer in vegetable production systems. Therefore, it is imperative to find suitable approaches to mitigate nitrogen leaching loss and soil acidity in vegetable production systems and promote nitrogen retention and vegetable nitrogen uptake for sustainable productivity. Biochar is a fine-grained and porous substance produced through pyrolysis processes, under oxygen-free conditions, from a wide range of biomass. In recent years, biochar has received more attention with regard to its capacity to increase crop yields by ameliorating the soil environment and regulating nutrient processes. According to previous studies, biochar is an option for mitigating soil acidity and nitrogen leaching problems in vegetable soils due to its alkalinity and adsorption properties. However, studies of biochar addition to vegetable production systems have not been well documented. The effect of biochar addition on leachate volume is still lacking. Whether the mineral nitrogen retained by biochar can be re-used by plants is still unknown. Few studies have investigated the effect of biochar addition on nitrogen processes and soil acidity under continuous growing conditions. Therefore, with the aim of determining the effect of biochar on soil nitrogen retention and vegetable nitrogen uptake, pakchoi was planted in a pot experiment during four continuous growing seasons with three biochar addition rates (0, 1% w/w and 5% w/w). In the 1st, 2nd and 3rd seasons, pakchoi was applied with 15N-labelled urea and in the 4th season no nitrogen fertilizer was provided. The results of this study were presented in four parts (soil nitrogen retention, soil acidity, vegetable nitrogen uptake and a distinction between two nitrogen sources in vegetable nitrogen uptake i.e. nitrogen left in the soil and nitrogen loss). The main conclusions are as follows: Biochar addition significantly increased the soil mineral nitrogen content by enhancing nitrogen retention in soils and soil nitrogen mineralization. Part of the mineral nitrogen retained by biochar was still bioavailable for plant uptake in the soil. Biochar significantly reduced nitrogen leaching loss by decreasing leachate volumes and nitrate concentrations in the leachate. Biochar addition significantly ameliorated or retarded soil acidity by promoting soil pH buffering capacity, reducing soil acidification rates and maintaining soil bases contents induced by biochar. The mitigation of soil acidity was not only as a result of biochar’s natural alkalinity but can also be attributed to the altered nitrogen processes (promotion of plant nitrate uptake, reduction of nitrification and nitrate leaching and maintaining soil bases contents) with the addition of biochar. Biochar’s mitigation of soil acidity was partly dependent on its effect on soil properties (such as bases contents) and processes (such as nitrification, nitrate leaching and plant nitrate uptake) rather than its natural alkalinity. Biochar maintained pakchoi yields and nitrogen uptake during four growing seasons. The fertilizer nitrogen recovery efficency was improved with an increase in the recovery of fertilizer nitrogen in the soil and the decrease in the recovery of fertilizer nitrogen in leachate. Fertilizer nitrogen was the major source for pakchoi nitrogen uptake, soil residual nitrogen and nitrogen leaching loss, while nitrogen from soil mineralization was the major nitrogen source for biochar retention. When nitrogen fertilizer was absent in the 4th season, the nitrogen fertilizer left in the soil from the 1st to 3rd seasons decreased sharply and fertilizer nitrogen retained by biochar was simultaneously released. The conclusion was that biochar addition could promote soil nitrogen retention and maintain high nitrogen uptake by vegetables in continuous growing seasons. However, the comprehensive effect of biochar on nitrogen loss still needs to be assessed before recommending extended utilization of biochar in vegetable production systems in China.
Conservation agriculture and its impact on soil quality and maize yield: A South African perspective.
(2018) Sithole, Nkanyiso Justice.; Magwaza, Lembe Samukelo.
The countries in sub-Saharan Africa (SSA) are faced with the problem of soil degradation resulting from unsustainable soil management practices such as conventional tillage (CT) and the removal of soil biomass from crop land. Conventional tillage leads to deterioration of important soil physical properties, the decline in soil organic carbon (SOC) and increase the risk of soil erosion. The reduction of SOC further affects soil macrofauna which has important key roles in soil processes such as soil structural formation, decomposition of soil organic matter (SOM) and recycling of soil important nutrients. This combined with water scarcity, low inherent soil fertility, increasing population and the predicted negative impacts of climate change poses threat to the regions ability to self-supply enough food for current and future generations. In response to this conservation agriculture (CA) has been endorsed because of its powerful mechanism to adapt by increasing resilience to land degradation, drought and increasing water use efficiency. Soils under no-till CA have been recognised widely that they generally contain higher SOC, the key principal indicator of soil quality, than CT system. These responses, however, are site-specific and depends on soil type, cropping systems, climate, fertilizer application and other management practices. Moreover, most of the published literature on the effect of CA on soil quality parameters comes from cooler temperate regions. As a result, the effect of CA on soil quality parameters in sub-tropical semi-arid environments remains unknown or controversial. Therefore, the primary objective of the study was to assess the effect of no-till (NT), rotational tillage (RT), CT and nitrogen fertilizer application rates on selected physical, chemical and biological properties of the soil and, their influence on maize yield. The secondary objective of the study was to explore the use of visible to near infrared spectroscopy (VIS-NIRS) as a possible cheap alternative for SOC quantification. The study was conducted at Bergville in KwaZulu-Natal Province of South Africa. The trial was established in 2003/04 growing season. This area forms the most important part of rainfed maize production in KwaZulu-Natal Province. The trial was arranged as a split plot with randomized tillage strips forming the whole plot and rate of application forming the sub-plots which are randomized within the whole plots. The experiment included three tillage treatments: 1) no-till (NT) with permanent residue cover, 2) annual conventional tillage (CT) and 3) rotational tillage (RT) every after four years. Nitrogen was applied at three rates, namely; 0 kg/ha, 100 kg/ha and 200 kg/ha. Lime ammonium nitrate (LAN) was used as a source of nitrogen. Unsuitable soil management in agriculture is known to results in deterioration of soil health and the decline in biodiversity. The objective of the study in soil biological properties was to assess the effect of no-till CA on the abundance and order diversity of soil macrofauna in continuous maize monocropping system. Soil macrofauna was sampled at the end of the 2015/2016 growing season using 25 × 25 × 25 cm steel monoliths. The mean density of individual orders was significantly higher (p < 0.001) under NT (46%) and RT (38%) compared with CT (16%). However, the Shannon-Weaver index (H, E index) revealed that the diversity and evenness of orders were similar, H= 2.6 and E~ 1, for all treatments. Macrofauna patterns revealed that NT and RT contained a significantly (p < 0.001) higher population of orders Isoptera and Diplopoda. Order Isoptera was 51% and 17% higher in NT than CT and RT, respectively while in Diplopoda, NT was 39% and 2% higher than CT and RT, respectively. It was concluded that NT and RT mulch-based system favoured the development of macrofauna communities in the studied maize continuous monoculture cropping system but did not favour order diversity of macrofauna. This suggests the importance of crop rotation for the development of the more diverse macrofaunal population. Soil degradation associated with the loss of soil organic carbon (SOC) has been a major concern in sub-Saharan Africa because of the subsequent yield reduction. The objective of the study in soil physical properties was to investigate the effect of NT, RT, CT and N fertilizer applications rate on soil aggregate stability, infiltration, SOC and its size fractions at 0-10, 10-20 and 20-30 cm depth. Soil samples were taken at the end of 2015/16 growing season using soil auger. On average, total SOC did not vary (p > 0.05) across the tillage treatments, 27.1 t/ha (NT) vs 26.0 t/ha (RT) and 26.6 t/ha (CT), but varied with depth where it was stratified in the 0-10 cm depth in NT and RT. Particulate organic C, however, varied significantly (p < 0.05) across the treatments where it decreased with increase in tillage intensity but only in the 0-10 cm depth. Mean weight diameter (MWD) was high under NT and RT and this was correlated to higher infiltration observed in these treatments. The results of this study showed that reduced soil disturbance improves physical protection of SOC, soil structure and infiltration. Soil management practice may change soil chemical properties and thus fertility. The magnitude of change varies depending on soil type, cropping systems, climate, fertilizer application and management practices. The objective of this study on soil chemical characteristics was to assess the effects of tillage systems, residue retention and fertilizer application rates on the amount and distribution of soil major nutrients in the 0-10, 10-20 and 20-30 cm depth. The soil samples were taken at the end of 2015/2016 growing season using soil auger and transported to the University laboratory for chemical analysis. The concentration of total Nitrogen (N) followed the same trend as that observed in soil physical properties. SOC and N were found to be concentrated on the soil surface (0-10 cm depth). Phosphorus was significantly higher (p < 0.001) under NT (0.0213 t/ha) than in RT (0.0127 t/ha) and CT (0.00704 t/ha). A large amount of P was in the 0-10 cm depth in NT and it was distributed more uniformly under RT and CT. Potassium was also higher (p < 0.05) under NT (9.73 t/ha) than in CT (8.00 t/ha) and RT (9.52 t/ha). It was found to be uniformly distributed across the soil depths in all tillage treatments. The soils from NT and RT had lower pH values than CT at 0-10 cm depth while increased significantly in the lower depths. Cation exchange (CEC) capacity followed the same trend. The results indicated that NT treatment increased nutrient availability in the studied soil which was more linked to the distribution of SOC and variability of pH along the soil profile, thus this indicating the potential of implementing NT in the semi-arid environment. Resilient and sustainable soil management systems are needed to overcome soil degradation, arrest soil fertility decline and to offset the predicted negative impact of climate change. This study investigated the long-term (13 years) impact of soil quality parameters (soil physical, chemical and biological properties), N fertilizer application rate and rainfall on maize grain yield. On average (across the years) maize yields were higher in NT (12.3 t/ha) and RT (12.4 t/ha) under higher rate on N fertilizer application (200 kg/ha) than CT (11.8 t/ha). However, yields decreased in NT with the reduction of N fertilizer application rate in medium N rate (100 kg/ha) and low rate (0 t/ha). The yields decreased by 1.7 t/ha, 1.4 t/ha and 0.4 t/ha from high N application rate (200 t/ha) to medium N application rate (100 t/ha) in NT, RT and CT, respectively. Under low rainfall of < 400 mm/year and high N application rate (200 kg/ha), the yield was 9.13 t/ha, 7.96 t/ha and 7.00 t/ha in NT, RT and CT, respectively across the years. However, when the average rainfall was above 600 mm/year, yields averaged at 13.3 t/ha, 13.7 t/ha and 13.5 t/ha in NT, RT and CT under high N fertilizer application rate across the years. Principal component analysis (PCA) was performed to VI assess some biological, physical and chemical properties of the soil that contributed to maize yield. The results showed no parameter that seemed to be related to maize yield. This was attributed to the complex interaction of bio-physio-chemical parameters with the environment. The results of this study found that yields improve over time under CA and this was more pronounced during the drought period. Yields improvements under CA require the application of the higher rate of N fertilizer in correct amount. Therefore, it is recommended that CA is implemented in semi-arid subtropical areas to improve soil conditions, water conservation and to achieve optimum yields. Application of spectroscopy for assessment of soil nutrition in the field may be affected by the depth at which the radiation spreads to, the analysed nutrient, and management practices such as tillage systems. The visible to near infrared spectroscopy (VIS-NIRS) was explored as a technique to predict soil organic carbon (SOC) and soil organic nitrogen (SON) in soils differing in soil tillage management practices. Partial least square regression (PLSR) models were developed using the leave-one-out cross validation method. The models were then tested on independent samples (54) randomly selected from the total 324 samples. The best prediction model was observed for SOC with the coefficient of determination (R2) = 0.993, root mean square error of prediction (RMSEP) = 0.157% and residual predictive deviation (RPD) = 2.55 compared with R2= 0.661, RMSEP= 0.019%, RPD= 2.11 for SON. Considering the predictive statistics and accuracy created by the model in the prediction of SOC, VIS-NIRS can be recommended as a fast, accurate technique for SOC determination in the studied soil. This will significantly reduce the cost associated with SOC and SON analysis for researchers and farmers. UKUFINYEZWA KWENDABA YONKE JIKELELE Amazwe asezansi ne Afrikha abhekene nengwadla enkulu yokudicileka phansi nokuphelelwa umsoco komhlabathi. Lokuphelelwa umsoco komhlabathi kubangelwa izindlela zokutshala ezingalungile ezingahlali isikhathi eside njengokutshala lapho oqale ulime umhlabathi khona bese usebenzisa igeja ususe nokhula. Lokhukulima ngegeja bese ususa ukhula kubangela ukuthi umhlabathi unganothi ngoba usuke ususe amacembe namagatsha agayekile (noma ayimvuthuluka) abaluleke kakhulu ekwakheni inqalasizinda sokuthi umhlabathi ubumbane ubeyimbumba futhi ukwazi ukuthi unikeze izitshalo umsoco wokuthi zikhule kahle. Lezizimvuthuluka zezitshalo um
Emerging and new pests under climate change in Limpopo Province, South Africa.
(2018) Phophi, Mutondwa Masindi.; Mafongoya, Paramu L.
Vegetable production is constrained by pests such as weeds, insects and diseases. The damage caused by pests and diseases can be highly exacerbated by climatic changes and variability. Poor agricultural practices play a role in increasing greenhouse gas emissions which contribute to climate change. Climatic factors such as increased temperature, increased carbon dioxide levels and erratic rainfall are responsible for influencing pest distributions, pest migration and increased pest population. Distribution and migration of pests can also result from globalization, trade and movement of people. Poor biosecurity and phytosanitary measures are also involved in bringing new pests in countries. This study was conducted in Limpopo Province in four municipalities of Vhembe District (Mutale, Musina, Makhado and Thulamela). Quantitative and qualitative techniques were used in data collection. Data was collected through questionnaire surveys, focus groups discussions and key informants. Farmers were randomly selected from a list provided by extension officers in each municipality. Three focus groups were conducted in each municipality consisting of seven women, seven men and a combined group of seven men and women. Statistical Package for Social Sciences (SPSS) was used to compare mean differences between different variables. Means and significant differences between means were declared at P ≤ 0.05. The aim of this study was to evaluate the presence of new and emerging pests in Limpopo Province. The major objectives of the study were to evaluate farmer’s perception on climate change and new and emerging pests, to determine the control measures used by farmers to manage vegetable insect pests, to evaluate the role of institutions on insect pest management, and to determine new and emerging pests in the district. Results of the study indicated that long dry spells, late rainfall and warmer winters were major indicators of climate change in Limpopo Province. Famers in all municipalities perceived aphids as major problematic insect pests to vegetables and were not significantly different from each other (P > 0.05). The highest percentage of aphid prevalence was found in Mutale municipality (82.1%) and the lowest was found in Thulamela municipality (66.7%). Tuta absoluta (South American tomato pinworm) and Spodoptera frugiperda were reported as new insect pests in Vhembe District. Tuta absoluta was only reported in Musina municipality. Spodoptera frugiperda was significantly higher in Makhado irrigated system (72%) and was significantly different from Musina municipality (8.3%) and Thulamela dryland system (19%). Bagrada hilaris (bagrada bug) and Acanthoplus discoidalis (armoured bush cricket) were observed as emerging pests in the district. Thulamela dryland system (73%) was significantly different from Thulamela irrigated system (33%) and Musina municipality (41%) in terms of Bagrada hilaris prevalence. Musina municipality (50%) was significantly different from the rest of the municipalities with respect to Acanthoplus discoidalis prevalence (P < 0.05). The lowest prevalence of amoured cricket was found in Mutale irrigated system (9.52%). All municipalities showed that they highly depended on chemical control for pest management. All municipalities except Makhado dryland system, mentioned that chemicals were effective for insect pest management. The percentage of farmers who agreed that chemicals were effective was significantly different from farmers who did not agree that chemicals were effective (P < 0.05). The overall study showed that climatic factors increased the prevalence of insect pests in Limpopo Province. High temperatures could have influenced the population and distribution of insect pests. New insect pests observed seemed to have quickly adapted to climatic factors in Limpopo Province and therefore, resulted to severe damage on host crops. The study also emphasized that chemical control was effective for insect pest management. However, farmers were over applying pesticides to kill insect pests. This resulted in high levels of pesticide resistance. Frequent application of pesticides can be harmful to the environment and to human health, and can also increase the level of pesticide residues on vegetables. More studies need to be conducted on the biology of new and emerging insect pests in Limpopo Province. Awareness on new and emerging insect pests must be raised to assist farmers in preparedness on how to manage insect pests. Farmers need to be trained more on chemical control measures and other control measures such as integrated pest management and biological control for pest management. The government should also train extension officers on climate change and insect pests, climate smart agriculture and effects of pesticides in order to deliver relevant advisory services to farmers.
Water use and nutritional water productivity of selected major and underutilised grain legumes.
(2018) Chibarabada, Tendai Polite.; Modi, Albert Thembinkosi.
Grain legumes have potential to alleviate the prevalence of food and nutrition security in water scarce areas. There is need to promote underutilised grain legumes to diversify crop production and build resilience. This requires knowledge on their water use (ET), environmental adaptation and nutritional content (NC) in comparison to major legumes. The study benchmarked underutilised grain legumes [bambara groundnut (Vigna subterranea) and cowpea (Vigna unguiculata)] to major grain legumes [groundnut (Arachis hypogaea) and dry bean (Phaseolus vulgaris)] with respect to ET, water productivity (WP), NC and nutritional water productivity (NWP). Field experiments were conducted during the 2015/16 and 2016/17 summer seasons under varying water regimes [optimum irrigation (OI), deficit irrigation (DI) and rainfed (RF)] and environmental conditions (Ukulinga, Fountainhill and Umbumbulu) in KwaZulu-Natal, South Africa. Data collected included stomatal conductance, leaf area index, timing of key phenological stages and yield. Water use was calculated as a residual of the soil water balance. Water productivity was calculated as the quotient of grain yield and ET. Grain was analysed for protein, fat, Ca, Fe and Zn. Yield, ET and NC were used to compute NWP. Results from the field trials were used calibrate and test the performance of AquaCrop model for groundnut and dry bean. Under varying water regimes, crops adapted to limited soil water through stomatal regulation and reduction in canopy size and duration. Yield, yield components and WP varied significantly (P < 0.05) among crop species. During 2015/16, groundnut had the highest yield and WP under DI (10 540 kg ha-1 and 0.99 kg m-3, respectively). During 2016/17, the highest yield and WP were observed in dry bean under DI (2 911 kg ha-1 and 0.75 kg m-3, respectively). For both seasons, dry bean had the lowest ET across all water treatments (143 – 268 mm). Dry bean and groundnut out–performed bambara groundnut with respect to yield, harvest index and WP. Yield varied significantly (P < 0.05) across environments and seasons. Cowpea was the most stable species. Results of NWP were significant among crops (P < 0.05). Yield instability caused fluctuations in NWP. Groundnut had the highest NWPfat (46 – 406 g m-3). Groundnut and dry bean had the highest NWPprotein (29 – 314 g m-3). For NWPFe, Zn and Ca, dry bean and cowpea were more productive. Overall, the AquaCrop model was successfully calibrated for groundnut and dry beans. Model testing showed AquaCrop’s potential for simulating growth, yield and ET of groundnut and dry bean under semi-arid conditions. Underutilised grain legumes need to undergo crop improvement for successful promotion. There is need to improve adaptation of grain legumes to different environments and resilience to extreme weather events. Future studies should consider benchmarking more underutilised grain legumes to major grain legumes.
The efficacy of Moringa oleifera plant extracts against selected fungal and bacterial plant pathogens infecting selected vegetable crops in Zimbabwe.
(2018) Goss, Maria.; Mafongoya, Paramu L.; Gubba, Augustine.
Diseases and pests are among the major constraints to horticultural production worldwide, and this has been further exacerbated by mono-cropping production systems in response to increased food demands of an ever-expanding population. As a result, farmers have resorted to excessive chemical use in order to manage diseases and pests, and maintain high yields. However, excessive chemical use has been associated with negative environmental and health effects. Numerous studies have been carried out to determine antifungal and antibacterial properties in traditional medicinal plants aimed at developing bio-pesticides which can be utilized together with synthetic pesticides in integrated disease management strategies. One such alternative is the use of Moringa oleifera extracts. Currently, in-vitro studies carried out on Moringa antimicrobial action have mainly focused on controlling human enteric pathogens. It is against this background that this study was conducted during the 2014 – 2016 cropping seasons. The main objectives of the study were to: 1) determine farmers’ perceptions on vegetable disease incidence, prevalence and disease control methods in relation to seasonality and prevailing climactic conditions. 2) Evaluate effectiveness of Moringa leaf and seed plant extracts in suppressing growth and development of bacterial (Pectobacterium atrosepticum, Hall, Pectobacterium carotovorum subspp. brasilienses, Bur., Dickeya dadantii, Dick.) and fungal (Pythium ultimum, Trow., Rhizoctonia solani, Kuhn., Fusarium solani, Mart., Phytophthora infestans, Mont.) plant pathogens in-vitro. 3) Determine whether Moringa aqueous extract concentration influences the efficacy of its antimicrobial activity. 4) Determine whether Moringa bark aqueous extracts could exhibit antibacterial activity against four different pathovars of the Xanthomonas campestris, Pammel., pathogen. 5) Determine the antifungal and antibacterial efficacy of Moringa leaf, seed and bark aqueous extracts against selected fungal and bacterial pathogens infecting two crops Lettuce (Lactuca sativa, L.) and Cabbage (Brassica olearacea, L.) grown under greenhouse and open field conditions respectively. Initially, a survey was carried out to determine the perceptions of horticulture farmers on crop disease incidence and control methods in the sub-humid areas of Zimbabwe. Survey results revealed that farmers face more outbreaks of fungal diseases compared to bacterial diseases. In addition, farmers have noted an increase in disease incidence over the past 5 – 10 years. The survey further revealed that the majority of the respondents depend on chemicals to control diseases in their crops. Only a small percentage of the farmers use cultural or mechanical alternative disease control methods. However, none of the respondents utilize botanical or bio-pesticide disease control strategies to manage these diseases. There is need to raise awareness among farmers regarding the negative health and environmental effects of increased chemical use and the potential of using bio-pesticide strategies in plant disease management. Field and greenhouse trials were conducted over three growing seasons using the completely randomized block and split plot experimental designs set up as factorial trials. The laboratory results exhibited the efficacy of Moringa leaf, bark and seed aqueous extracts in significantly controlling the growth of fungal (Pythium ultimum, Rhizoctonia solani, Fusarium solani and Phytophthora infestans) and bacterial (Pectobacterium carotovorium subspp. brasiliensis, Pectobacterium atrosepticum and Xanthomonas campetris pv campestris) pathogens. There were significant interactions between Moringa aqueous extract source and concentration which influenced the antimicrobial action of the extracts (P = 0.001). The results from the greenhouse and field studies revealed that Moringa leaf, seed and bark aqueous extracts significantly controlled bottom rot (Rhizoctonia solani) and stem/root rot (Fusarium solani) diseases in lettuce and black rot disease (Xanthomonas campestris pv campestris) in cabbages (P < 0.05). Disease suppression was more effective at higher concentrations of the Moringa aqueous extracts, whilst the highest disease severity occurred at the lowest Moringa aqueous concentration levels. However, Moringa seed aqueous extract demonstrated higher antibacterial activity against black rot disease and antifungal activity against test pathogens (P < 0.05). Moringa seed and leaf aqueous extracts also significantly enhanced head weight and diameter in lettuce. Moringa aqueous extracts can therefore be considered as bio-pesticides in Integrated Crop Disease Management strategies, and these can be a viable, and environmentally friendly alternative to chemical use. Based on our findings, it is recommended that further in-vivo studies to improve extraction protocols, and determine ideal application methods be carried out to improve Moringa aqueous extract bio-pesticide efficacy. These should be carried out in selected crop pathogens of economic importance. Currently, there is very little literature regarding in-vivo crop, pathogen and bio-pesticide interaction studies with Moringa. Training workshops and demonstration plots to impart knowledge and skills to farmers on preparation and utilization is key to enhance uptake.
The responses of insect pests to a changing and variable climate in Zimbabwe.
(2017) Chapoto, Rumbidzai Debra.; Mafongoya, Paramu L.; Gubba, Augustine.
Abstract available in PDF file.
Intergration of management practices towards improving hybrid maize yield, quality and nutritional compositions under rain-fed condition.
(2017) Akinnuoye-Adelabu, Dolapo Bola.; Modi, Albert Thembinkosi.
Maize (Zea may L.) is an important staple crop grown under different ecological conditions by both large-scale commercial and smallholder farmers in Southern Africa. The current changes in climatic conditions may propel farmers to shift from their convectional planting windows and harvesting period, which may have resultant effect on the seed yield and quality. Hence, it is important to understand how maize production responds to climate change. This study evaluated interaction of planting date and soil fertility level on maize (Zea mays L. cv. SC701) morphological, physiological and yield parameters. Field trials were conducted during the 2014/15 and 2015/16 seasons at two sites under dryland conditions to compare the effects of early season, mid-season and late season planting dates on these parameters under different soil fertility levels. In addition, yield, kernel nutritional value and seed quality were determined in response to different maturity stages. Results showed a significant interaction between planting date and fertiliser application on crop growth and quality. The study indicated that maize production is more sensitive to planting date, which is linked to a lack of optimum temperature for growth than fertiliser application. However, optimum soil fertility can be used to attain a better seed quality under sub-optimal planting date.

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