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Crop Science

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Browsing Crop Science by Author "Buckley, Christopher Andrew."

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    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.
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    Vertical hydroponic production of leafy vegetables with human-excreta-derived-materials (HEDMs) from decentralised sanitation technologies.
    (2020) Sihlongonyane, Sisekelo Simo.; Magwaza, Lembe Samukelo.; Odindo, Alfred Oduor.; Buckley, Christopher Andrew.; Yeh, Daniel H.
    Hydroponic production of leafy vegetables with human-excreta-derived-materials (HEDMs) extracted by decentralised sanitation technologies is projected to reduce food shortages while improving sanitation services in peri-urban communities, particularly in informal settlements. This study investigated the potential use of HEDMs generated by decentralised sanitation technologies for hydroponic production of leafy crops. HEDMs generated by decentralised sanitation technologies, namely: Anaerobic Baffled Reactor (ABR) and Nutrients, Water and Energy Generator (NEWgenerator) were used as treatments. A vertical hydroponic system called ZipGrow Farm Wall was assembled to conduct horticultural trials at Newlands Mashu Research site in Durban, South Africa. The vertical hydroponic system had eight vertical growing towers. Four vertical growing towers were fertigated with commercial hydroponic fertiliser mix (CHFM) as a control and the other four fertigated with HEDM as a treatment. A literature review was undertaken on open field and hydroponic production of crops with HEDMs. Previous and current studies indicated that nutrients derived from human-excreta have the potential to support the growth of plants even though low yields are obtained in some instance, and faecal pathogen contamination in crops occurs due to fertigation with infected nutrients. Only drip irrigation systems were reported to limit the transfer of faecal pathogens from nutrient source to plants. The first research study investigated the potential use of anaerobic baffled reactor (ABR) effluent on growth and yield of Swiss chard in a vertical hydroponic system. The results revealed that Swiss chard grown with CHFM performed better than those in ABR effluent and gave a significantly (p<0.05) higher plant height and fresh yield. Fresh leaf mass of Swiss chard was reduced in ABR effluent by 78 % when compared to CHFM. Sodium toxicity, ammonium toxicity, aphids and flea beetles reduced the growth and yield of Swiss chard grown with ABR effluent. Amaranthus in planted wetlands of ABR system hosted aphids and flea beetles who moved to defoliate matured Swiss chard leaves grown with ABR effluent as they thought it is a similar crop. In contrast, Swiss chard fertigated with CHFM suffered minimum effects of pest outbreak due to absence of faecal smell and nutrient stress. The second research study investigated the potential of diluted NEWgenerator permeate + hydroponic fertiliser (DNP + HF) on growth, and yield of hydroponically grown non-heading Chinese cabbage. The results revealed there was no significant difference in all determined growth parameters except for fresh yield (p>0.05) between plants fertigated by CHFM and DNP + HF. Fresh leaf mass of non-heading Chinese cabbage leaves was reduced in DNP + HF by 26 % when compared to CHFM. Significant yield decline in non-heading Chinese cabbage grown with DNP + HF was a result of nutrient conditions affecting the uptake and accumulation of nutrients in leaf tissues. Plant analysis revealed that uptake of macronutrients and micronutrient significantly varied in leaf tissues of non-heading Chinese cabbage between fertigation with CHFM and DNP + HF. Leaf tissues of non-heading Chinese cabbage showed higher levels of N, P, Mg, Mn, Na, Cu, Fe and Al while lower levels of K, Ca and Zn were observed when compared to plants grown with CHFM treatment. The deficiency and toxicity of nutrients in leaf tissues led to interference in photosystem activity of non-heading Chinese cabbage grown with DNP + HF which resulted on decline in final yield. On a positive note, harvested leaves were without faecal coliforms. These findings show that fertigation with ABR effluent and DNP + HF has the potential to support the growth of leafy vegetables in a hydroponic system. However, there is a need for further research to look at other aspects with negatively affected the final yield of crops.