Crop fertigation (nitrogen and phosphorus) with decentralised wastewater treatrment system effluents and effects on soil and groundwater.

Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.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) 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 0.8, MAE 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

Effect of ABR effluent irrigation on Swiss chard (Beta vulgaris subsp. cicla) growth and nutrient leaching.

M. Sc. Agric. University of KwaZulu-Natal, Pietermaritzburg 2014.The Decentralised Waste Water Treatment System (DEWATS) is used in countries such as India and Indonesia for the treatment of human waste. The waste is passed through a series of baffles where it is anaerobically degraded, resulting in the production of the Anaerobic Baffled Reactor (ABR) effluent. Disposal of the effluent can still pose a challenge if not done properly and lead to environmental pollution. The effluent has been shown to contain high concentrations of mineral elements such as nitrogen and phosphorus, which are important for plant growth. There is little information on the use of effluent for agriculture particularly under the South African climatic and edaphic conditions. This study investigated the effect of using ABR effluent on the nutrient uptake, growth and yield of Swiss chard (Beta vulgaris subsp. cicla) on selected soil types. Field and tunnel experiments were carried out at Newlands Mashu Permaculture Centre in Durban (longitude of 30°57'E and latitude of 29°58'S). The initial experiment planted in the summer season of 2012 was designed to collect baseline data on growth and yield of Swiss chard and other selected crops under rain-fed vs. irrigated conditions using tap water. The treatments were laid out using a randomised complete block design (RCBD) with three replications. The treatments included: tap water irrigation without fertiliser application (TW); tap water irrigation with fertiliser application (TWF) and rain-fed with fertiliser application (RFF). The second experiment was conducted in winter 2012 with the aim of investigating growth and yield of Swiss chard irrigated with ABR effluent during the dry season. In the second study, the treatment “tap water irrigation without fertiliser application” was substituted with irrigation with ABR effluent while the other treatments were maintained. The third experiment was conducted in the summer season of 2013. The treatments remained similar to those of the winter 2012. Soil samples were collected from the top 30 cm before planting and after harvesting for chemical analyses. A neutron probe access tube was also installed in the middle of each plot in order to monitor soil water status and irrigate plots according to the root zone soil water deficit. Wetting Front Detectors (WFDs) were installed at 30 cm and 50 cm depths to monitor nutrient leaching. The leachates collected by WFDs were analysed for nitrates and phosphates using Merck Reflectoquant test kit. Similarly, the ABR was analysed for its chemical composition before each irrigation event. Treatment effect on Swiss chard and soil was tested by analysing fresh crop biomass, dry biomass, chlorophyll content, crop nutrient uptake and soil chemical properties. Parallel studies were conducted in a tunnel to investigate growth and yield response of Swiss chard grown on different soils (acidic, clayey loam and sandy loam soil) treated with varying fertiliser rates. The experiment was laid out as a factorial treatment structure with the following factors: Irrigation source (2 levels); soil type (acidic, clayey loam and sandy loam soil) and fertiliser application rate (No fertiliser, half-optimum recommended rate and optimum recommended rate based on soil analyses) replicated four times. The Swiss chard was grown in the tunnel in pots for 11 weeks. Crop growth and chlorophyll data, similar to that collected from the field was also collected from the pot trials. Data analysis was done using GenStat® 14th Edition (VSN International, Hemel Hempstead, UK). The results from the baseline study (experiment 1) did not reveal significant differences between treatments (TW, TWF and RFF) thus suggesting that the inherent soil fertility was high and could support Swiss chard growth. There were significant differences (P<0.05) between the treatments (ABR, TWF and RFF) during the winter season (experiment 2) with respect to Swiss chard biomass. Swiss chard plants produced under rain-fed conditions had lower dry mass compared with those that were irrigated using ABR effluent and tap water with fertiliser. However, the effect of using ABR effluent on Swiss chard biomass was comparable to tap water with fertiliser because these did not differ significantly. The results from the third experiment showed a lack of significant differences with respect to N and P leaching between the irrigation sources (ABR, TWF and RFF). Controlled experiments in the tunnel revealed a significant interaction between soil type and irrigation source. Swiss chard pots containing acidic soil and irrigated using the effluent showed significantly higher dry mass (P < 0.01), fresh mass (P< 0.05) and leaf area index (P < 0.001) compared to those irrigated with tap water. In conclusion the ABR effluent may have a liming effect which could have possibly increased Swiss chard growth in acidic soil. ABR effluent was more useful as an irrigation source in winter than in summer; however in summer the effluent could be more useful as a fertiliser source in areas where water is not limiting for crop production. N and P leaching and uptake could not be associated with irrigation using ABR effluent

Modelling nitrogen and phosphorus dynamics in soil fertigated with decentralised wastewater treatment effluent

Many residents in informal settlements lack proper sanitation. The decentralised wastewater treatment system (DEWATS) is a low-cost water borne onsite technology that can potentially provide sanitation in unserved areas. The management of DEWATS effluent is of environmental concern. Its use in agriculture helps improve livelihood and food security in peri urban areas. This study investigated environmental sustainability for fertigation using DEWATS effluent through modelling N and P dynamics in fertigated soils. The SWB Sci model, a crop growth and nutrient (N and P) simulation model was calibrated and validated based on field experiments conducted. The crop growth sub-model was successful and met all statistical criteria (r2 > 0.8 and D > 0.8). Use of DEWATS effluent showed to increase soil inorganic N and P within the top soil layers (0.3 m), which may be beneficial for crop production. However, proper management practices are recommended to prevent leaching and runoff losses

Nitrogen and phosphorus dynamics in plants and soil fertigated with decentralised wastewater treatment effluent

Municipalities in South Africa face problems in providing sanitation to unserved informal settlements in peri-urban areas and rural nodes. The Decentralised Wastewater Treatment System (DEWATS) connected to community ablution blocks can be an option, with the treated effluent then applied to agricultural land. However, the management of treated wastewater through irrigation of crops must be environmentally sustainable. This study therefore investigated nitrogen (N) and phosphorus (P) dynamics in soil irrigated with DEWATS effluent. A field study with banana and taro in a randomised complete block design with three blocks and two irrigation treatments (DEWATS effluent without fertiliser vs tap water + fertiliser) was carried out over a period of 992 days at the Newlands-Mashu Research Site, Durban, South Africa. Data were collected on crop N and P uptake, soil chemical properties, and nutrient leaching together with groundwater monitoring. Nitrogen and P uptake was not significantly different (p > 0.05) between the two irrigation treatments. Irrigation with DEWATS effluent increased soil N and P concentrations within the upper 0.3 m implying its importance as a fertiliser source. Leaching of N and P from DEWATS effluent treated plots was comparable to that from the tap water + fertiliser treatments. However, to manage excess water in the soil, practices such as irrigation to meet crop water requirements with room for rainfall and installation of subsurface drainage when possible can be employed.The Water Research Commission, South Africahttp://www.elsevier.com/locate/agwat2020-04-20hj2019Plant Production and Soil Scienc

Suitability of the Decentralised Wastewater Treatment Effluent for Agricultural Use: Decision Support System Approach

The decentralised wastewater treatment system (DEWATS) is an onsite sanitation technology that can be used in areas away from municipal sewerage networks. The discharge of effluent emanating from DEWATS into water bodies may cause pollution. Agricultural use of the effluent may improve crop yields and quality thereby contributing to food security in low-income communities. There are drawbacks to the agricultural use of treated wastewater. Therefore, the study assessed the crop, environmental and health risks when irrigating with anaerobic filter (AF) effluent using the Decision Support System (DSS) of the South African Water Quality Guideline model, in four South African agroecological regions, three soil types, two irrigation systems and three different crops. The model was parameterised using AF effluent characterisation data and simulated for 45 years. The model predicted that there are no negative impacts for using AF effluent on soil quality parameters (root zone salinity, soil permeability and oxidisable carbon loading), leaf scorching and irrigation equipment. The problems were reported for nutrient loading (N and P) in maize and microbial contamination in cabbage and lettuce. It was recommended that the effluent should be diluted when used for maize production and advanced treatment should be explored to allow unrestricted agricultural use

Residues from black soldier fly (Hermetia illucens) larvae rearing influence the plant-associated soil microbiome in the short term

The larvae of the black soldier fly (BSFL, Hermetia illucens) efficiently close resource cycles. Next to the nutrient-rich insect biomass used as animal feed, the residues from the process are promising plant fertilizers. Besides a high nutrient content, the residues contain a diverse microbial community and application to soil can potentially promote soil fertility and agricultural production through the introduction of beneficial microbes. This research assessed the application of the residues on plant-associated bacterial and fungal communities in the rhizosphere of a grass-clover mix in a 42-day greenhouse pot study. Potted soil was amended with BSFL residues (BR+) or conventional compost (CC+) produced by Rwandan waste management companies in parallel to residues and compost sterilized (BR-, CC-) by high-energy electron beam (HEEB) as abiotic controls. The fertilizers were applied at a rate of 150 kg N ha−1. Soil bacterial and fungal communities in both fertilizer and soil were assessed by high-throughput sequencing of ribosomal markers at different times after fertilizer application. Additionally, indicators for soil fertility such as basal respiration, plant yield and soil physicochemical properties were analyzed. Results showed that the application of BSFL residues influenced the soil microbial communities, and especially fungi, stronger than CC fertilizers. These effects on the microbial community structure could partly be attributed to a potential introduction of microbes to the soil by BSFL residues (e.g., members of genus Bacillus) since untreated and sterilized BSFL residues promoted different microbial communities. With respect to the abiotic effects, we emphasize a potential driving role of particular classes of organic matter like fiber and chitin. Indeed, especially taxa associated with decomposition of organic matter (e.g., members of the fungal genus Mortierella) were promoted by the application of BSFL residues. Soil fertility with respect to plant yield (+17% increase compared to unamended control) and basal respiration (+16% increase compared to unamended control) tended to be improved with the addition of BSFL residues. Findings underline the versatile opportunities for soil fertility arising from the application of BSFL residues in plant production and point to further research on quantification of the described effects.ISSN:1664-302

Data_Sheet_1_Residues from black soldier fly (Hermetia illucens) larvae rearing influence the plant-associated soil microbiome in the short term.pdf

The larvae of the black soldier fly (BSFL, Hermetia illucens) efficiently close resource cycles. Next to the nutrient-rich insect biomass used as animal feed, the residues from the process are promising plant fertilizers. Besides a high nutrient content, the residues contain a diverse microbial community and application to soil can potentially promote soil fertility and agricultural production through the introduction of beneficial microbes. This research assessed the application of the residues on plant-associated bacterial and fungal communities in the rhizosphere of a grass-clover mix in a 42-day greenhouse pot study. Potted soil was amended with BSFL residues (BR+) or conventional compost (CC+) produced by Rwandan waste management companies in parallel to residues and compost sterilized (BR-, CC-) by high-energy electron beam (HEEB) as abiotic controls. The fertilizers were applied at a rate of 150  kg N  ha−1. Soil bacterial and fungal communities in both fertilizer and soil were assessed by high-throughput sequencing of ribosomal markers at different times after fertilizer application. Additionally, indicators for soil fertility such as basal respiration, plant yield and soil physicochemical properties were analyzed. Results showed that the application of BSFL residues influenced the soil microbial communities, and especially fungi, stronger than CC fertilizers. These effects on the microbial community structure could partly be attributed to a potential introduction of microbes to the soil by BSFL residues (e.g., members of genus Bacillus) since untreated and sterilized BSFL residues promoted different microbial communities. With respect to the abiotic effects, we emphasize a potential driving role of particular classes of organic matter like fiber and chitin. Indeed, especially taxa associated with decomposition of organic matter (e.g., members of the fungal genus Mortierella) were promoted by the application of BSFL residues. Soil fertility with respect to plant yield (+17% increase compared to unamended control) and basal respiration (+16% increase compared to unamended control) tended to be improved with the addition of BSFL residues. Findings underline the versatile opportunities for soil fertility arising from the application of BSFL residues in plant production and point to further research on quantification of the described effects.</p