Masters Degrees (Soil Science)

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A laboratory and glasshouse investigation on the effect of liming with fly ash and processed stainless steel slag on two contrasting South African soils.
(2008) Ndoro, Esina Tambudzayi.; Hughes, Jeffrey Colin.
Soil acidity is a major land degradation problem that limits crop production globally. The high cost of traditional liming materials (calcitic limestone, dolomite etc.) and the vast areas of land that require liming have led to the exploratory utilisation of alkaline industrial by- products such as fly ash and stainless steel slag. The liming potential and effects of liming with fly ash (from the Duvha power station) and processed stainless steel slag (Calmasil) on two acid soils were investigated in this study. The quality of fly ash and Calmasil as liming materials and their potential impacts on the soil quality and plant growth were investigated. The effects of liming with these materials on soil pH, EC, extractable Al, Mn, base cations and trace elements were investigated in an incubation experiment. A glasshouse trial was conducted to assess the effects of these materials on the growth of an acid intolerant crop, perennial rye grass. The incubation and glasshouse study were of a factorial design with two acid soils (the Avalon and Inanda soils), three materials (fly ash, Calmasil and lime); and five application rates of 0, 50, 100, 200 and 400% of the recommended optimum liming rate (OLR) for the growth of perennial rye grass. Characterization of fly ash showed that the major elements (>5%) present (Si > Al > Fe) are not comparable to lime (Ca > Si > Mg) and that it has a low liming potential (calcium carbonate equivalence (CCE) of 9.6%) in comparison to lime. The chemical composition of Calmasil is comparable to lime with Ca > Si > Mg as the major elements and it has a very high liming potential (CCE = 97%). The incubation experiment showed that adding fly ash and Calmasil increased the pH of both soils. However, at the optimum liming rate (100% OLR), only the treatment with Calmasil in the Avalon soil attained pH levels within the desired pH range. Extractable Al and Mn decreased with addition of fly ash and Calmasil to levels comparable to lime in the incubated soils. Addition of fly ash and Calmasil also increased the extractable base cations of both soils. The yield-response of perennial rye grass to treatments in both soils was in the following order: fly ash > Calmasil > lime. Application of fly ash at > 200% OLR in the Avalon soil caused injury of ryegrass. Application of fly ash and Calmasil at lower rates has great agronomic potential in ameliorating soil acidity.
Analysis of global gully characteristics and the impacts of gabions and grass on sediments and carbon storage.
(2018) Dube, Hastings Bangani.; Muchaonyerwa, Pardon.; Chaplot, Vincent A. M.
Abstract available in PDF file.
Assessing decomposition and soil carbon sequestration potential of sorghum residues from different cultivars.
(2022) Ntonta, Sipho.; Zengeni, Rebecca.; Muchaonyerwa, Pardon.; Chaplot, Vincent A. M.
Abstract available in PDF.
Assessing the effect of in-field rainwater harvesting on soil physico-chemical properties and crop yield in comparison with the traditional farmers’ practice.
(2017) Khuzwayo, Mduduzi.; Zengeni, Rebecca.; McCosh, Jon Stuart.
Most communal farmers in South Africa rely on rain-fed agriculture. However, the country is experiencing rainfall variability as well as low soil fertility. These are major limiting factors to food production especially since South Africa is dominated by a semi-arid climate. It is for this reason that rural communities must optimally utilise their limited water reserves. Rainwater harvesting (RWH) technologies are amongst possible alternatives to maximise agricultural crop production. The aim of this study was to assess the effect of in-field rainwater harvesting on selected soil physico-chemical properties and maize crop yield in comparison with the traditional farmer practice. The study was conducted in homestead gardens in Kwa-Zulu Natal (KZN) province, under Msinga local municipality and in Eastern Cape Province (EC), under Tsolo local municipality. The study was set up at five homestead gardens namely Madosini, Beya, Mjali, Quvile and Sokhombe in the Eastern Cape and three field trials in Kwa-Zulu Natal (Mntungane, Xoshimpi and Mxheleni). It was designed as randomised complete block design, that compared in-field rainwater harvesting (contour ridges) with the traditional farmer practice (control) over two seasons (2013/14 and 2014/2015). Data was collected for soil chemical and physical properties as well as for crop grain and dry matter yields. Soil samples were collected at 0 - 10, 10 - 20 and 20 - 30 cm depths for analysis of soil pH, exchangeable bases, micronutrients and aggregate stability, and for analysis of bulk density at 0 -10 cm. These samples were collected at planting (2013) and at harvesting (2015). Gravimetric soil moisture content was periodically monitored at different stages of maize growth (planting, vegetative growth, tasselling and harvesting) in 2015. Biomass and grain yield were determined at harvest. Results showed that rainwater harvesting improved soil moisture content, aggregate stability, grain and dry matter yields. No clear trend was observed on the effect of rainwater harvesting on exchangeable bases, soil pH and micronutrients across all study sites in Kwa-Zulu Natal and Eastern Cape. It was therefore recommended that rainwater harvesting be used by resource constrained rural farmers who are experiencing unfavorable precipitations to improve crop yields and soil productivity.
Assessing water use effeciency and carbon sequestration potential of different wheat (Triticum aestivum) genotypes.
(2019) Mbava, Nozibusiso Odette.; Zengeni, Rebecca.
Poor soil fertility status and limited water availability have been identified as two of the major constraints to crop production in South Africa. Under these conditions, growing crop genotypes that will sequester more carbon into the soil and be more water use efficient is crucial to improve crop production thus alleviate food insecurity. The aim of the study was to assess water use efficiency and carbon sequestration potential of different wheat genotypes. The experiment was set up under field and greenhouse conditions using 100 wheat genotypes from CIMMYT. These were grown at 25% (water-stressed) and 75% (non-stressed) field capacity (FC) using an alpha lattice with 10 blocks and 10 genotypes per block. Treatments were replicated twice in the field and three times in the glasshouse. After harvest the 10 best wheat genotypes were separated into roots and shoots, their chemical composition was analysed prior to the incubation experiment. About 0.25 g each of wheat root (RT) or shoot (ST) of the selected wheat genotypes were thoroughly mixed with 100 g of soil then transferred into an air tight PVC pot. NaOH solution was also placed inside the incubation pot to trap CO2 released during decomposition, and this was measured on day 0, 7, 15, 23, 31, 39, 47, 55, 63, 77, 91,105, and 120 of incubation. The results from the field and glasshouse experiments showed that average wheat grain yield (GY) varied from 326 g m-2 to 2062 g m-2, shoot biomass (SB) ranged from 1873 g m-2 to 3726 g m-2 while total plant biomass (PB) ranged from 2992 g m-2 to 6289 g m-2. Grain carbon stocks (GCS) averaged 132 g C m-2 and 167 g C m-2 in the glasshouse under stressed and non-stressed conditions, respectively. The total plant carbon stocks (PCS) ranged from 691 g m-2 to 3093 g m-2 (i.e. 348% difference) in the glasshouse, while they ranged from 835 g m-2 to 4016 g m-2 (i.e. 381% difference) in the field. Water use efficiency for grain yield production (WUE-GY) ranged from 0.12 g m-2 mm-1 to 2.10 g m-2 mm-1 (i.e. 18 fold increase) in the glasshouse under stressed conditions while it was 0.57 g m-2 mm-1 to 4.01 g m-2 mm-1 in the field under stressed conditions. WUE components varied amongst wheat genotypes. LM75 exhibited higher WUE-GY under stressed conditions while genotypes LM48 and LM47 exhibited lower WUE-GY under non-stressed conditions. LM75 was also ranked the best genotype for WUE-PCS while BW162 was ranked the best genotype for WUE-RCS. In the incubation experiment the shoot treatments evolved higher net CO2-C compared to root treatments. Net CO2-C was highest within the first two weeks and declined with time. Amongst the root treatments, BW140 RT evolved the highest net CO2-C (86.6 mg CO2-C kg-1 soil), while LM70 RT evolved the lowest (48.8 mg CO2-C kg-1 soil). In shoot treatments BW162 ST and BW140 ST evolved the highest net CO2-C with average values of 218.7 and 223.8 mg CO2-C kg-1 soil respectively. Comparing all the 10 treatments LM70 RT evolved the lowest while BW140 ST and BW162 ST had the highest net CO2-C. The findings revealed that variability in storing C under different scenarios of water availability exists among the wheat genotypes studied. Also, the residues of different wheat residues exhibit potential of sequestering more C into the soil thus improve soil fertility.
Characterisation of potato waste biochars and effect on carbon dioxide emission, liming potential and availability of primary macro-nutrients of two amended contrasting soils.
(2021) Vilakazi, Samukelisiwe Pinky.; Muchaonyerwa, Pardon.; Dube, Nkosinomusa Nomfundo.
Abstract available in pdf.
The characterisation of some South African water treatment residues and glasshouse pot experiments to investigate the potential of two residues for land disposal.
(2003) Titshall, Louis William.; Hughes, Jeffrey Colin.
Water treatment residues (WTRs) are the by-product from the production of potable water. They consist mainly of the precipitated hydrous oxides of the treatment chemicals, and materials removed from the raw water. This study investigated the range of treatment processes and residues produced in South Africa, and two WTRs were selected for testing on selected soils and mine materials. A questionnaire was developed and sent to water treatment authorities across South Africa. Information on the treatment chemicals, dosages, volumes and current disposal practices, and a sample of WTR from each treatment plant were requested. Eleven, of 21 authorities, returned completed questionnaires, representing 37 water treatment facilities. Organic polymers were the most commonly used treatment chemical, with most plants also using lime. Other less frequently used chemicals and additives were A12(SO4)3.14H2O, Fe2(SO4)3, FeC1), sodium aluminate, activated silica, activated charcoal, CO2 and bentonite. Information given regarding residue thickening and disposal was poor. Samples from Rand Water, Umgeni Water (Midmar), Midvaal Water Company, Amatola Water and Cape Metropolitan Council (Faure) were received or collected. An additional sample from Faure was also received, representing a change in the treatment process. These samples were analysed for a range of chemical and physical characteristics. These analyses showed that the WTRs had the potential to supply some plant nutrients (Ca, Mg, Fe, S) but that metal toxicity may be a problem, in particular Mn in the Faure WTR, and that P adsorption may be severe. The samples selected to test the potential for land disposal were from Rand Water and Faure. A pot experiment tested the growth of Eragrostis teff, Cenchrus ciliaris and Digitaria eriantha in mixtures of Rand WTR and material from a coal mine i.e., a sandy soil material, spoil material and coal combustion ash, at rates of 0, 50, 100, 200 and 400 g kg-1 with a uniform fertiliser treatment applied to all mixtures. The grass was harvested on three occasions and the mean total yield (dry mass) determined, as well as nutrient uptake. The pots were leached after each harvest and the pH and electrical conductivity determined. The soil, spoil and ash were characterised and pH, EC and water retention characteristics of the mixtures determined. Growth of the grasses in the ash treatments was poor and these were terminated. Eragrostis teff grown in the soil showed a decrease in mean total yield with increasing WTR application rate, but yield was good up to the 200 g kg-1 treatment at the first harvest, declining substantially by the second harvest. In general C. ciliaris and D. eriantha grown in the soil showed a decrease in mean total yield for all harvests with increasing WTR application. The yield of E. teff, grown in the spoil, increased up to 100 g kg-1 WTR addition, but decreased thereafter. Digitaria eriantha showed a decrease in yield, and C.ciliaris an increase, with increasing WTR application rate, but for all treatments the differences were non-significant. The pH and EC of the leachates generally increased with increasing WTR addition. The concentration of nutrients in the grasses did not indicate any deficiencies or toxicities. As the growth of grass was poor in the ash treatments, another pot experiment was established to test the growth of two creeping grass species grown in the Rand WTR as a cover over the ash material. Cynodon dactylon and Stenotaphrum secundatum were grown in 20, 40 and 60 mm layers of Rand WTR, with and without a fertiliser treatment. Both species performed best in the 60 mm layer with fertiliser, and C. dactylon performed better than S. secundatum. The former species was more tolerant of the high pH, but both have potential as cover vegetation on the ash dumps when these are covered with Rand WTR. A further glasshouse study investigated the effect of Faure WTR mixed with a nutrient poor sandy soil on the nutrient uptake and seed yield of common dry beans (Phaseolus vulgaris). The WTR was added to the soil at 0, 50, 100, 200 and 400 g kg-1 each with five levels of fertiliser (0, 25, 50, 100 (recommended optimum) and 150 %). Bean pods were harvested once the plants had senesced. The number of pods and mass and number of seeds per treatment were determined. The seeds were analysed for nutrient uptake. Interveinal chlorosis and necrotic lesions were evident on cotylendonous and new leaves in the WTR treated soils, the severity of the symptoms increasing with increasing rate of WTR. Additional pots were established at the 400 g kg-1 rate (without fertiliser) and leaf material collected for chemical analysis. This showed that Mn toxicity was the cause, with leaf concentrations about 12 times the recommended 100 mg kg-1 upper limit. However, mass of bean seed was highest in the 400 g kg-1 Faure WTR treatment with 150 % fertiliser. Nutrient translocation to the seed seemed to be relatively consistent regardless of treatment, with little accumulation of Mn. The data collected illustrated the range of conditions and types of WTRs produced in South Africa, and that in some instances these residues have favourable characteristics for land application. The use of the Rand WTR showed that it could be applied to the spoil medium at relatively high concentrations without severely negatively impacting on grass growth, but that more caution should be used when applying this material to the soil medium. While the grass did not grow in the ash treatments, it would seem that with suitable species the Rand WTR could be beneficially applied to ash material as a cover layer. The use of the Faure WTR on a sandy soil seemed to potentially improve the yield of the indicator crop, but caution should be exercised due to the possibility of Mn toxicity. The use of additional fertiliser would seem to be essential. Further research would require that field scale investigation of both WTRs be conducted, as well as further studies of application rates and techniques in laboratory and glasshouse investigations.
Chemical characteriistics, fertilizer value and escherichia coli and salmonella composition of vermicomposted sewage sludge.
(2016) Mashologu, Busisiwe.; Muchaonyerwa, Pardon.
Abstract available in PDF file.
Comparative effects of sugarcane monoculture on soil organic matter status and soil biological activity.
(2002) Dominy, Carol Susan.; Haynes, Richard John.
The effects of increasing periods under sugarcane monoculture (managed by preharvest burning) on soil organic matter content and related soil properties were investigated in the 0 to 10 cm layer of a sandy coastal Ochric Cambisol (Glenrosa soils) and a red Rhodic Ferralsol (Hutton soil) from the sugar belt of KwaZulu-Natal. The organic C content at both sites under undisturbed vegetation is about 48 g C kg-I. This declined exponentially with increasing years under sugarcane. For the Glenrosa site, organic C reached a new equilibrium level of about 20 g kg-I while at the Hutton soil the equivalent value was 41 g kg-I. The higher organic matter content maintained at the Hutton site was attributed mainly to clay protection of organic matter since the clay content of the Hutton soil was 61 % compared to the 18 % for the Glenrosa soil. The loss of soil organic matter under sugarcane resulted in a concomitant decline in soil microbial biomass C, microbial quotient, basal respiration, aggregate stability, arylsulphatase and acid phosphatase activity. The activities of arylsulphatase and acid phosphatase like those for concentrations of microbial biomass and organic C, were higher for the Hutton than Glenrosa soils. At the Glenrosa site, the natural OBC abundance in soils was used to calculate the loss offorest-derived, native soil C and the concomitant input of sugarcane-derived C. Sugarcane-derived C increased over time until it accounted for about 61 % of organic C in the surface 10 cm in soils that had been under sugarcane for greater than 50 years. The effects of agricultural land use (including burnt sugarcane) on organic matter content and related soil properties were compared with those under undisturbed native grassland in KwaZulu-Natal. Two separate farms situated on Oxisols were used and both contained fields with continuous long-term (>20 years) cropping histories. At site 1, soil organic C content in the surface 10 cm followed the order permanent kikuyu pasture> annual ryegrass pasture> native grassland> preharvest burnt sugarcane > maize under conventional tillage (CT). At site 2, organic C in the surface 20 cm decreased in the general order kikuyu pasture> native grassland > annual ryegrass pasture> maize under zero tillage (ZT) ~ maize (CT). Organic C, microbial biomass C, microbial quotient, basal respiration and aggregate stability were substantially greater in the surface 5 cm under maize ZT than maize CT. In the undisturbed sites (eg native grassland and kikuyu pasture) the metabolic quotient increased with depth. By contrast under maize CT and sugarcane there was no significant stratification of organic C, yet there was a sharp decrease in metabolic quotient with depth. Aggregate stability was high under both native grassland and kikuyu pasture and it remained high to 40 cm depth under the deep-rooted kikuyu pasture. Although soil organic C was similar under maize CT and sugarcane, values for microbial biomass C, microbial quotient, basal respiration and aggregate stability were lower, and those for metabolic quotient and bulk density were higher, under sugarcane. This was attributed to the fallow nature of the soil in the interrows of sugarcane fields. It was concluded that the loss of soil organic matter, microbial activity and aggregate stability is potentially problematic under maize CT and sugarcane and measures to improve organic matter status should be considered. For sugarcane, this could include green cane harvesting and the use of green manure crops in rotation.
A comparative study of the BCR sequential and batch extractions for wastes and waste-amended soil.
(2010) Elephant, Dimpho Elvis.; Bester, H. Christopher.; Titshall, Louis William.
The use of standard soil tests to assess waste materials has become a common practice in waste management. However, the suitability of using standard soil tests on waste materials is questionable. Therefore, this investigation was undertaken to compare commonly used chemical extraction methods for their ability to extract elements from soil, waste, and soil-waste mixtures. This was carried out by: · Assessing the effects of extraction time on the extractability of Al,Ca, Co, Cu, Fe, Mg, Mn, Ni, Pb, S, Si, and Zn; · Assessing the comparability between single and sequential extraction. Two manganese rich wastes namely electro-winning waste (EW) and silicate-rich smelter slag (SS) and an acid soil (Inanda, Ia) were used for this study. Waste amended soils were obtained by incubating the EW and SS with Ia soil at field capacity at a rate of 20 g kg-1 and 120 g kg-1 soil respectively, and were sampled at day 0, 7, 28, 56, and 140. The effect of extraction time was assessed on the EW, SS, and Ia soil with carbonated water used in the acid rain test conducted at 16, 20, 30, and 50 hours. The equilibration time was different for different materials and elements. The concentration of Al and Zn did not change appreciably with increasing extraction time in the EW. Similar results were found for Mg, S, and Si in the SS and S in the Ia soil. This was attributed to ‘equilibrium’ being reached before 16 hours. The equilibration time of 20 hours which would release the exchangeable and specifically adsorbed elements was obtained for Co, Mg, Si, S, and Mn in the EW. The concentration of Ca decreased with extraction time in the EW and was attributed to readsorption. The concentration of Ca and Mn in the SS and Al, Fe, and Si in the Ia soil increased with extraction time and the ‘equilibrium’ was not reached even after 50 hours. This was attributed to the release of elements due to dissolution of minerals. In the comparison between Community Bureau of Reference (BCR) sequential and batch extraction, the concentrations of Ca, Co, Mg, Mn, and S were higher in batch extraction than in sequential extraction, particularly for the EW and the EW treated soils. This was possibly caused by the readsorption of released elements during water extraction. On the contrary, sequential extraction had higher concentration of Al and Fe compared to batch extraction for the EW, Ia soil, SS treated soils, and EW treated soils. These were attributed to a continued desorption of elements and dissolution of minerals due to exposed surfaces which occurs in sequential extraction. The comparison between single and sequential extraction for the BCR sequential extraction showed that hydroxylammonium chloride (HAC) applied in sequential extraction had higher concentration of Al, Co, Fe, Pb, and Zn than the single HAC extraction. This was probably due to incomplete dissolution of minerals, precipitation of amorphous minerals, and readsorption of released elements occurring for a single HAC extraction. These were minimised for hydrogen peroxide (H2O2) extraction and hence comparability between single and sequential H2O2 extraction was observed. This was probably due to the presence of complexing agent in the extracting reagent which would minimise the formation of secondary precipitates and hence, improved dissolution of minerals was obtained. Similarly, the concentrations of elements were comparable between single and sequential aqua regia extraction. These results indicated that comparability is improved between single and sequential extraction when aggressive conditions are used. The results from this investigation indicated that when chemical extraction methods are applied to wastes, the effects of the waste properties on the results of extraction need to be well understood. Consequently, when the chemical extraction methods are used in waste management scenarios certain modifications might have to be made. These modifications include the use of a high solution:solid ratio and an extracting solution which has high complexing ability
Comparison of selected extractants for potassium requirement factor and evaluating potassium equilibria for soil testing and fertilizer recommendations.
(2020) Msane, Londeka Truth Thobeka.; Nongqwenga, Nqaba.; Muchaonyerwa, Pardon.
Abstract available in PDF.
A comparison of soil and foliar-applied silicon on nutrient availability and plant growth and soil-applied silicon on phosphorus availability.
(2006) Matlou, Mmakgabo Cordelia.; Haynes, Richard John.
A greenhouse study was carried out to investigate the effectiveness of soil-applied silicon (Si) with that of foliar applications for sorghum growth. Silicon sources were soil-applied as calmasil (calcium silicate) at two rates (4 and 8t/ha) and foliar applied Si including pure K-silicate, K-humate and K-fulvate (all three foliar treatments at rates of 300 and 600 ppm). Another treatment included soil applied calmasil plus low rate of foliar applied K-humate. The soils used for the greenhouse trial were Cartref, Glenrosa, Nomanci and Fernwood. Results indicated that application of calcium silicate to the soil before planting increased sorghum yield and Si uptake in three of the four soils. Silicon uptake from different experimental treatments followed the order: Calmasil 8t/ha > calmasil 4t/ha ~ calmasil + 300 ppm K-humate> K-humate = K-fulvate = pure-K silicate = control. Foliar sprays were ineffective at increasing yield, Si content of the plant tissues or Si uptake. The concentrations of exchangeable Ca, Mg as well as soil pH were significantly increased by calmasil treatments. Extractable AI concentrations were also reduced due to the Iiming effect of calcium silicate and also possibly formation of insoluble aluminosilicates. The yield response to applied calmasil seemed to be primarily related to its Iiming effect and reductions in extractable AI in the Cartref, Glenrosa and Nomanci soils. The dry matter yield was highest in Fernwood and lowest in Cartref soil. However, there was no significant yield response to calmasil in Fernwood soil which had an initial pH of 5.8 and insignificant extractable AI concentrations. Therefore application of calcium silicate had no significant effect on extractable AI concentration in this soil. Yield response to calmasil may also have been partly due to direct positive effects of applied Si on crop growth through mechanisms such as increased photosynthetic rate and reduced transpiration rate, Addition of calmasil increased the concentrations of Si in the plant tissues and reduced those of N, P and Kin Nomanci and Fernwood soils respectively. This indicates that nutrient interactions were occurring in the plant. It was concluded that foliar-application is not an effective way of applying Si to a Siresponsive crop such as sorghum when growing in soils low in extractable soil Si. This is because Si is accumulated in plant tissues in similar amounts to macronutrients. It was also concluded that in future, studies of crop response to applied Si should include the use of non-Iiming source of Si (e.g. silicic acid) so as to separate a liming effect of calcium silicate from effect of applied Si. In a laboratory study, the effects of applied silicic acid, calcium silicate and calcium hydroxide on levels of extractable P in two Si-deficient soils were investigated. Two soils (Fernwood and Nomanci soils) were treated with two rates of P and three soil amendments (calcium silicate, calcium hydroxide and silicic acid) and incubated for six weeks at room temperature. Phosphorus was extracted using Truog, AMBIC and resin methods, and levels of exchangeable and solution AI and extractable and solution Si were also measured. Application of calcium silicate and calcium hydroxide increased soil pH in both soils while silicic acid additions had no significant effect compared with the control. The pH increase was much greater in the Fernwood than Nomanci soil because of the low buffering capacity of the sandy Fernwood soil. Exchangeable AI and concentrations of monomeric and total AI in soil solution generally followed the order: control ~ silicic acid> calcium silicate> calcium hydroxide. The lowering of soluble AI concentrations in the silicic acid treatments was attributed to formation of insoluble aluminosilicate compounds while that in the calcium silicate and calcium hydroxide treatments was attributed to their Iiming effects causing a rise in pH. Concentrations of Si in soil solution were lower in the calcium hydroxide than the control treatment suggesting the solubility of Si decreased with increased pH. Additions of both Si sources increased Si concentrations in solution and the effect was more marked for the calcium silicate treatment. This was attributed to formation of insoluble aluminosilicates in the silicic acid treatment. Concentrations of H2S04extractable Si with treatment did not closely follow the same trends as those for Si concentrations in soil solution. That is, levels of extractable Si were very much higher in the calcium silicate than silicic acid treatment in both soils. In addition, concentrations of extractable Si in the calcium hydroxide treatment were similar to control in the Nomanci soil, while for the Fernwood soil, concentrations in the calcium hydroxide treatment were exceptionally high. It was suggested that liming with calcium silicate or calcium hydroxide had rendered some Si-containing compounds in the soil acid-extractable and that the nature of acid-extractable Si fraction need further study in future. The quantities of P extracted from the two soils by the various extractants followed the order: Truog> AMBle> resin. The greatest increase in extractable P induced by additions of P was recorded for Truog P and the least for resin P. The effects of Iiming (addition of calcium silicate or calcium hydroxide) on extractable P levels differed depending on the soil and extractant used with increase, decrease or no effect being recorded. Such results confirm the complexity of lime and P interactions which occur in acid soils. Additions of silicic acid had no effect on levels of extractable P, compared to control. It was suggested that the reason for this was that phosphate is adsorbed to AI and Fe oxide surfaces much more strongly than silicate. As a result, additions of Si are ineffective at increasing extractable P levels.
A comparison of soil extraction methods for predicting the silicon requirements for sugarcane.
(2007) Kanamugire, Andre.; Meyer, J. H.; Haynes, Richard John.
Although silicon (Si) has not yet been recognized as an essential nutrient element, its application to sugarcane (Saccharum officinarum L.) has proved to be beneficial. Since optimum crop production depends on the maintenance of adequate plant nutrients in the soil, there is a need in the South African sugar industry for a reliable index for assessing the requirement for supplemental silicon (Si) in soils, particularly in reducing the risk of Eldana saccharina stalk borer infestation in cane. The objective of this study was to assess Si availability in soils, to select a suitable Si extraction method and a critical value for determining when a response is likely. For this purpose, five acid soils (representing. some of the most important agricultural soil groups used for sugarcane production in the sugar belt) were used in October 2004, in the lAKE WILSON glasshouse of the South African Sugarcane Research Institute (SASRI) based at Mount Edgecombe. Except for the Arcadia form soil with an initial Si content of 1.2 mmol kg- I as estimated using the O.OlM H2S04 + (NH4)zS04) extractant, soils representing the other five soil forms namely Cartref, Glenrosa, Longlands and Nomanci; exhibited a sub-optimal Si content of not more than 4.0 mmol kg-I. Sorghum was used as a plant crop and sugarcane as a ratoon crop because of their Si accumulator status. Three different Si sources: calmasil, slagment and wollastonite; with respectively 9.85, 15.20, and 5.25% Si content were applied at increasing rates of 0, 3 and 6 tons ha- 1 as Si fertilizers. Silicon (Si) was extracted from untreated and treated soils by utilizing six different extractants, (1) O.OlM H2S04 + (NH4)2S04; (2) Distilled water; (3) 0.025M H2S04; (4) 0.5M CH3COOH; (5) 0.5M CH3COONH4pH 4.8; and (6) O.OlM CaCh.2H20. The amount of soil Si extracted followed the order: 0.025M H2S04 > 0.5M CH3COOH > O.OlM H2S04 + (NH4)2S04 > O.OlM CaCh.2H20 > 0.5M CH3COON~ pH 4.8 > distilled water. Soil Si extracted by 0.025M H2S04 was significantly correlated with soil exchangeable cations,. CEC, clay content, cane biomass yield, cane Si uptake and increasing rates of applied Si. Averaged over all soil forms investigated, the increases in dry biomass yield and Si uptake ranged. from 18% to 154% for sorghum; and from 23% to 85% for cane respectively. Even though the highest increases (%) in cane biomass yield and Si uptake were obtained on a Nomanci form soil with initial poor fertility status, the highest means were obtained on an Arcadia form soil with the highest Si initial content. There was no difference between different Si sources in their ability to influence cane biomass yield and Si uptake, and therefore the supply to the soils. Even though the lower and higher Si source rates were not different from each other, they increased cane yield and Si uptake, indicating that Si was undoubtedly beneficial for sugarcane. The Si critical levels for different soils as estimated by 0.025M H2S04 were 6.0 mmol kg-1 (168 mg kg-I) for Arcadia; 2.6 mmol kg-I (64 mg kg-I) for Cartrel; 2.5 mmol kg-I (64 mg kg-I) for Glenrosa; 1.6 mmol kg-I (45 mg kg-I) for Longlands; and 2.4 mmol kg-I (67 mg kg-i) for Nomanci form soils.
A comparison of the effects of tillage on soil physical properties and microbial acitivity at different levels of nitrogen fertilizer at Gourton Farm, Loskop, KwaZulu-Natal.
(2010) Bassett, Terri Storm.; Titshall, Louis William.
Long-term food security and environmental quality are closely linked to maintaining soil quality. Therefore, the assessment of the effect of agricultural management practices on soil chemical, physical and biological parameters provide fundamental information about sustainability. An agricultural management practice which has received much attention in the last decade is tillage. The loss of topsoil due to erosion and a reduction of soil organic matter under conventional tillage practices, together with escalating fuel prices, have lead to the increased implementation of conservation tillage practices. However, the response of soil to a reduction in tillage is dependent on the inherent soil properties, environmental conditions, crop type and the land management practices. The successful implementation of conservation tillage practices is thus site specific. Furthermore, the effect of fertilizer application on soil quality is affected by tillage regime and therefore has important implications for recommendations of fertilizer application rates. The objectives of this study were to investigate the effect of tillage regime at three rates of nitrogen fertilization on soil microbial activity and selected soil physical properties in the Loskop area of KwaZulu-Natal, South Africa. Based on the outcomes of these investigations, recommendations regarding sustainable tillage practice and nitrogen fertilizer application rate are made. A field trial was initiated in 2003 on Gourton Farm in the Loskop area of KwaZulu-Natal on an area that was previously under annual conventional tillage and is currently planted to dry-land maize. The trial was arranged as a split plot experimental design with tillage regime (whole plots) replicated three times, and fertilizer type and application rate forming randomized subplots within the whole plots. The trial was on a clay loam soil type (Hutton soil form). The effects of annual conventional tillage (CT1) and no-till (NT) at three rates of nitrogen (N) fertilizer (as limestone ammonium nitrate (LAN)) applied at rates of 0 kg N ha-1 annum-1 (0N), 100 kg N ha-1 annum-1 (100N) and 200 kg N ha-1 annum-1 (200N) were evaluated for their effects on soil organic carbon (SOC), microbial activity, bulk density (ñb), water retention characteristics, saturated hydraulic conductivity (Ks), micro-aggregate stability and soil penetration resistance. Undisturbed soil cores were taken from three inter-rows in triplicate from each sub-plot for the A horizon (0 to 20 cm) and from three inter-rows in duplicate for the B horizon (20 to 40 cm). These undisturbed soil cores were used to determine the ñb, water retention characteristics and Ks. Bulk soil samples were collected from three inter-rows in triplicate from each sub-plot for the A (0 to 20 cm) and B (20 to 40 cm) horizons. The bulk samples from each horizon in each sub-plot were thoroughly mixed and halved. One half was used to determine microbial activity as measured by the hydrolytic and cellulolytic activity and the other half was used to determine SOC content, particle size distribution and aggregate stability. Penetration resistance was taken in duplicate in three rows in each sub-plot at 1 cm increments to a depth of 50 cm or until an instrument limiting penetration resistance of 5000 kPa was reached. Tillage regime and N application rate considerably affected soil microbial and physical properties in the A horizon (0 to 20 cm). The SOC, hydrolytic activity and ñb are significantly greater (P 0.05) effect on the soil microbial activity and physical properties except for Ks, where the Ks is significantly (P 0.05) in the B horizon on the measured soil microbial activity and physical properties except for the penetration resistance. Increasing levels of fertilizer resulted in increased penetration resistance throughout the soil profile under NT. Under CT1, this same trend is evident from below the plough layer. These results indicate that the microbial activity, as measured by hydrolytic and cellulolytic activity, is improved under NT compared to CT1. Furthermore, the soil under NT retains more plant available water (PAW) and although the ñb and penetration resistance are greater there was no obvious adverse effect on maize growth. In addition, a high rate of LAN fertilizer adversely affected soil microbial and physical properties, especially under NT. Therefore, it is proposed that NT is the preferred tillage practice in providing long-term sustainability and soil health without causing negative soil structural properties for crop productivity in the short-term. In addition, it is recommended that although increased levels of nitrogen fertilizer results in higher yielding maize plants it is unsustainable to apply high applications of LAN due to the negative effect on the soil microbial and physical properties and thus there is a need to re-evaluate the sustainability of using high rates of LAN to increase crop yields, especially under NT systems.
Effect of long-term application of nitrogen and liming on soil carbon dynamics in a semi-arid grassland.
(2022) Buthelezi, Kwenama.; Buthelezi, Nkosinomusa Nomfundo.
Abstract available in PDF.
The effects of burning or mulching of harvest residues on selected soil properties in a Eucalyptus plantation in Northern KwaZulu-Natal.
(2014) Madikizela, Siphamandla.; Hughes, Jeffrey Colin.; Titshall, Louis William.; Rietz, Diana Nicolle.; Podwojewski, Pascal.
The sustainable management of commercial forest resources is required to ensure long-term soil fertility and the productivity of later rotations; this includes soil nutrient retention and the protection of soil structure. A major factor in the protection of soil structure is the distribution of soil organic carbon (SOC) and nutrients, as well as the stability of soil aggregates. These are influenced by forest harvest residue management practices such as the removal, displacement on the soil surface, or burning of residues. Soil aggregate stability is an important soil property that gives a reliable estimation of the ability of soils to respond to external forces such as rainfall, wind, and land management. The objectives of the study were to investigate the effect of forestry residue management methods on selected soil properties and their effect on soil structural stability under the previous stump-line and in the current inter-row. The results obtained from the study will contribute to understanding the effects of forest harvest residue management on some soil properties. The study site was near Paulpietersburg, northern KwaZulu-Natal, South Africa. A trial was established by the Institute for Commercial Forestry Research (ICFR) in 2010 to investigate the effect of tree harvest residue management, soil compaction and its amelioration through ripping, on the growth of Eucalyptus dunnii grown on a Magwa soil form. This trial has a factorial treatment design and consists of three soil disturbance treatments (no compaction, compaction, and compaction with amelioration) and two residue management practices (burning and residue mulching), with four replicates (24 treatment plots). The effect of burning and mulching harvest residue on selected soil properties and soil aggregation in relation to other soil properties was studied two years after the treatments were established. For the purposes of the present study, the no-compaction treatment and both residue management treatments (burning and mulching) were used (eight plots). Bulk samples, 192 in total, were collected from each of the eight plots, from both the current inter-row and the old stump-line, at a depth of 0 to 0.1 m and 0.1 to 0.2 m using a spade. Samples were air dried and sieved to collect soil aggregates between 2 and 8.5 mm for soil aggregate stability determinations by determination of the mean weight diameter (MWD). Some of the bulk sample was analysed for SOC, pH, exchangeable bases (Ca2+, Mg2+, K+, and Na+), and particle size distribution. Statistical analyses were carried out using Genstat and the results were regarded as significant if p < 0.05 (or 5%). Residue management had no significant (p ≥ 0.05) effect on exchangeable Mg2+, K+, and Na+, soil pH, exchangeable acidity, effective cation exchange capacity and texture. There was, however, a significant effect of residue management on SOC and exchangeable Ca2 Ca2+. Under the mulched plot treatment, SOC at the 0 to 0.1 m depth was significantly higher in soils when compared to the burned plot treatment. Under the burned plot treatment, exchangeable Ca2+ concentrations were significantly higher than the mulched treatment. Furthermore, under the burned plot treatment; exchangeable Ca2+ and Mg2+ concentrations were significantly higher in the 0 to 0.1 m depth than at the 0.1 to 0.2 m depth. Neither residue management strategy had any significant effect on MWD. However, there was a significant effect on MWD relating to soil depth and sampling position. Under both treatments, the MWD was higher at 0 to 0.1 m than at the 0.1 to 0.2 m depth, in both inter-row and stump-line samples. The average MWD of 2.45 mm (with a standard error of 0.04) and values that ranged between 0.8 and 3.5 mm was indicative of stable aggregates. Thus, surprisingly, no significant correlation was found between SOC and MWD. However, it was concluded that changes in residue management may alter SOC, thus impacting on the productivity of the soil. Furthermore, it was suggested that soil aggregate stability was driven by exchangeable Ca2+ and Mg2+.
Effects of irrigation-induced salinity and sodicity on soil chemical and microbial properties and sugarcane yield.
(2001) Rietz, Diana Nicolle.; Haynes, Richard John.
The effects of irrigation-induced salinity and/or sodicity on sugarcane yield, and two growth parameters, namely stalk height and number of nodes per stalk , were investigated on a sugarcane estate in the Zimbabwean lowveld. The effects of soil salinity and/or sodicity on the size, activity and metabolic efficiency of the soil microbial community was also studied. Furrow-irrigated fields which had a gradient in soil salinity and/or sodicity which increased from the upper to lower ends of the fields were selected for this study. This gradient was recognized by decreasing sugarcane growth down from the upper to the lower ends and the appearance of salt on the soil surface at the lower ends of fields. Sugarcane growth was classified as either dead, poor, satisfactory or good; and soil samples (0-0 .15 m, 0.15-0 .3 m, 0.3-0 .6 m and 0.6-0.9 m) were taken from each of these areas. Soils from under adjacent areas of undisturbed veld were also sampled. Sugarcane growth and yields in micro-plots of the various areas of the fields were measured. Foliar samples of sugarcane were taken at 22 weeks of age and analysed for nutrient content. Soil salinity and sodicity were quantified by measuring pH(water), electrical conductivity (ECe) and cation content of saturation paste extracts and the exchangeable cation content. From this information, the sodium adsorption ratio (SARe)and exchangeable sodium percentage (ESP) were also calculated. The calcareous, vertic soils in the study area under undisturbed veld were found to have high pH values (8 to 9.5), very high exchangeable Ca and Mg concentrations and there was evidence of accumulation of soluble salts in the surface 0.15 m. Under sugarcane production, irrigation induced salinity and sodicity had developed. Under poor and dead sugarcane, high values for ECe, SARe, and ESP were generally encountered in the surface 0-0 .3 m of the profile. In addition, the pH values under sugarcane were often between 9 and 10 particularly in profiles where sugarcane grew poorly or had died. As expected, pH was positively related to ESP and SARe, but negatively related to ECe. Measurements of aggregate stability by wet sieving, the Emerson dispersion test and the Loveday dispersion score all showed that soils from the study sited tended to disperse and that dispersion was most apparent where high ESP and SARe values occurred in association with elevated pH values and relatively low ECe values. These measurements confirmed observations at the sites of low infiltration rates and restricted drainage particularly on the lower ends of fields where sugarcane had died. In addition to the above measurements it was also observed that there was a rise in the watertable under furrow irrigation and that the watertable was nearest to the surface at the lower ends of the fields. In some cases the watertable was observed to be only 0.2 to 0.3 m from the surface. Thus, death of roots due to anaerobic conditions could be occurring to a greater extent at the lower ends of the fields. Another consequence of the high watertable was that these vertic soils were observed to remain in a permanently swollen state. This limits air and water movement in the soil profile as such soils need to be allowed to dry out and crack regularly so that macroporosity can be restored. Sugarcane yield, stalk height and number of nodes per stalk were not significantly related to ECe. Sugarcane yields were, however, significantly correlated with ESP and pH while stalk height and number of nodes were negatively correlated with ESP, SARe and pH. These results suggested that sodicity was a more limiting factor for sugarcane growth than salinity. Foliar analysis of leaf tissue did not reveal substantial differences in macro- or micro-nutrient content between good and poorly-growing sugarcane. It was concluded that the gradient of decreasing sugarcane growth down the furrow-irrigated fields, with crop death at the lower ends, was the result of a combination of factors. That is, the watertable had risen due to over-irrigation and it was nearer the surface at the lower ends of the fields. Due to capillary rise of salts, this resulted in sodic and sometimes saline-sodic conditions in the surface soil. These conditions could limit plant growth through ion toxicities, plant water stress and inhibition of root growth and function and physiological processes. These would be induced by the high pH and high salt, Na and HC03- concentrations in soil solution. Poor physical conditions associated with sodicity and the continually swollen state of the soils presumably limited infiltration and aeration in the surface soil, and probably restricted root growth. In addition, it is likely that the high watertable limited effective crop rooting depth to about 0.2 m at the lower ends of the fields. The net result was that sugarcane died at the lower ends. A negative effect of soil salinity and/or sodicity was also observed on the soil microbial population. Significant negative correlations were obtained with ECe SARe and ESP with microbial biomass C and microbial activity (as measured by FDA hydrolytic activity or arginine ammonification rate). The activity of enzymes involved in C (P-glucosidase), P (phosphatase) and S (arylsulfatase) mineralization and potential nitrogen mineralization (as determined by aerobic incubation) were also negatively correlated with these factors, with the exception of arylsulfatase activity and ESP. All the above mentioned microbial population measures were also positively correlated with soil organic C content, besides potential nitrogen mineralization. The metabolic quotient, which provides an indication of stress and efficiency of the microbial community, increased considerably with increasing salinity and sodicity and decreased with soil organic C. Thus, increasing salinity and/or sodicity resulted in a smaller, more stressed, less efficient microbial community, while the turnover rate and cycling of C, N, P and S also decreased. It was concluded that salt affected soil not only causes a decline in sugarcane yield through raising the concentration of soluble salts in soil solution, but also has a detrimental effect on microbial activity and on mineralization of soil organic C, N, Sand P.
Effects of land use change on soil and water quality and plant species composition of Cedara wetlands.
(2015) Ndayi, Phelisa.; Muchaonyerwa, Pardon.
Wetlands are vital in the provision of ecosystem services and land use change could affect their functioning and health. Disposal of organic waste slurries on wetlands could result in high nutrient loads, whereas drainage for agriculture, could adversely affect their characteristics, particularly soil properties. The purpose of this study was to assess the effects of land use changes on soil chemical properties, water quality and plant species composition of three wetlands at Cedara. One wetland was used for discharge of sewage effluent and dairy slurry; another was drained using ridge/furrow system and used for pasture production, while the third, undisturbed wetland, was used as the control. A soil survey was carried out to identify soil forms and soil sampling was done on transects at 0–20, 20–40, 40–60 and 60–100 cm depths, and the samples were analysed for pH, clay content, total C and N, CEC, exchangeable K, Ca, Na, Mg, available Mn, Zn, Cu and P. Water samples, taken during different seasons from upstream, midstream and downstream positions, were analysed for quality parameters. Grass species were identified for species composition. Wetland areal extends were greater when soil properties were used to delineate wetland bounderies than when diagnostic plant species were used. The dominant soil form in all wetlands was Katspruit, with Pinedene, Clovelly, Griffin and Hutton on the edges. Soils in all wetlands were acidic, with the drained wetland having higher pH, Ca and Mg concentrations. The dairy/sewage wetland had significantly higher P, Zn and Cu than the ridge/furrow drained wetland while the undisturbed wetland had the least. The undisturbed wetland had higher total C, N and available Mn concentrations than the other two. In the water samples pH, Ca, Mg and P was higher in the ridge/furrow drained wetland than the others. The undisturbed wetland had higher species composition and had more wetland plant species than the other wetlands which mostly had pasture grasses. The findings suggested that land use change will reduce soil C and N and available Mn, and modify the concentrations of available P and micronutrients and bases in the soil, impair water quality and ultimately result in loss of wetland plant species diversity.
Effects of long-term treatment with sewage sludge on concentrations of heavy metals in soil and tissue of selected plants, potential risks and implications for phyto-remediation.
(2016) Mbangi, Awonke.; Zengeni, Rebecca.; Muchaonyerwa, Pardon.
Abstract available in PDF file.
The effects of surface-applied poultry manure on top- and subsoil acidity and selected soil fertility characteristics.
(2001) Judge, Angus.; Haynes, Richard John.
The effects of surface applications of poultry manure on pH, exchangeable AI, exchangeable Al saturation and levels of available macronutrients in the surface and subsurface layers were investigated in some acid soils from the KwaZulu-Natal Midlands. Three field sites with a history of long-term applications of poultry manure were compared with adjacent fields where no manure had been applied. Results generally showed an increase in pHwater, pHKCI, exchangeable Ca, Mg, and K and extractable P and a decrease in exchangeable Al and exchangeable Al saturation in the surface soil to the depth to which the manure had been incorporated. Results also provided evidence for substantial downward movement of Ca and Mg into the subsoil layers (i.e. 30-60 cm) and their accumulation in exchangeable forms. There was a concomitant general increase in pHKcl and pHwater and decrease in exchangeable Al and exchangeable AI saturation in the subsoil layers. These results demonstrate that, under field conditions, surface applications of poultry manure can cause the amelioration of subsoil acidity. This is an extremely important finding since subsoil acidity is characteristically extremely difficult and costly to ameliorate. A leaching column study was subsequently conducted to investigate the mechanisms by which surface applications of poultry manure ameliorate both top- and subsoil acidity. The soil used, originating from one of the field sites, had not previously been treated with poultry manure and had a subsoil pHKCI of 4.25 and an exchangeable acidity concentration of 1.79 cmolJkg. Three forms of poultry manure (layer, broiler and free range) were incorporated into the surface 5 cm of soil columns at rates equivalent to 5, 10 and 30 Mg/ha. Columns were maintained in glasshouse conditions for a period of 108 days and over that period they were leached on four separate occasions (receiving a total of 825 mm of simulated rainfall). At the conclusion of the experiment, the soil columns were cut into sections for chemical analysis. Applications of poultry manure to the surface soil markedly increased pHwater, pHKcl, exchangeable Ca, Mg, K and Na concentrations and decreased exchangeable Al levels in the surface 5 cm layer. They also increased the concentrations of soluble C, soluble salts, total Al and organically-complexed Al in soil solution. These effects were most pronounced with layer manure and greater at the higher rate of application. The manure-induced decrease in exchangeable AI, but increase in total AI, in soil solution was attributed to soluble salts, originating from the manure, displacing exchangeable Al into solution where it was subsequently complexed by soluble organic matter. Analysis of subsoil layers (5-15, 15-25, 25-35 and 35-45 cm) at the conclusion of the experiment showed that surface applications of poultry manure decreased concentrations of exchangeable Al in the subsoil but had no effect on pHKCl and depressed values for pHwater. It was suggested that manure-derived urea leached into the subsoil and was then hydrolysed causing an increase in pH and precipitation of exchangeable Al as insoluble hydroxy-AI oxides. Towards the conclusion of the experiment nitrification began to proceed, causing subsoil pHKCl values to decrease back to their original values. Analysis of the inorganic-N content of leachates and soil layers provided circumstantial evidence for this mechanism. High concentrations of soluble salts in the subsoil layers (caused by leaching from the manure) resulted in displacement of exchangeable A13+ and W into soil solution so that the electrical conductivity and concentrations of total and monomeric Al were elevated and pHwater was depressed in the subsoil (15-45 cm) of poultry manure-treated columns. It was concluded that the results underline the opposing effects that poultry manure applications have on (i) raising soil pH and lowering exchangeable Al but at the same time (ii) greatly increasing soluble salt concentrations and thus displacing At3+ and H+ back into soil solution. They also have suggested the importance of the release of N during manure decomposition in influencing soil pH (through the processes of ammonification, urea hydrolysis and nitrification) and therefore other soil chemical properties. It is, however, clear that the long-term effect of surface applications of poultry manure is generally to ameliorate subsoil acidity by raising subsoil pH and lowering exchangeable Al concentrations.

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