Sustainable use of sewage sludge as a source of nitrogen and phosphorus in cropping systems

Municipal sewage sludge is used as source of plant nutrients world wide for agriculture. However, many countries do not make full use of this opportunity. A lack of local knowledge about the benefits and disadvantages of sludge contributes to this low utilisation. For instance, only 28% of the sludge produced in South Africa is beneficially utilized on agricultural lands. The overall objectives of this study were 1) to determine responsible sludge loading rates for a range of cropping systems 2) to investigate the agronomic benefits and sustainability of using municipal sludge according to crop N demand, and 3) to develop a tool to enable extrapolation of these results to other regions (soils, climates) and other cropping systems. Field experiments were conducted on a wide range of cropping systems including dryland maize, irrigated maize-oat rotation, dryland pasture, and turfgrass sod production. An 8 Mg ha-1 control (South African old annual upper limit norm) was compared with sludge rates of 0, 4, and 16 Mg ha-1 for the agronomic crops and dryland pasture. Under the turfgrass sod production, the aim was to export large volumes of sludge with the sod without compromising the environment. Therefore, an 8 Mg ha-1 control treatment was compared with sludge rates of 33, 67, and 100 Mg ha-1 which are equivalent to depths of 5, 10, and 15 mm sludge, respectively. Doubling of the old annual upper limit significantly increased grain and forage yield of both the dryland maize and the irrigated maize-oat rotation. This rate also improved weeping lovegrass hay yield, water use efficiency and crude protein content. Residual nitrate in the soil profile after harvest, and solution samples collected from wetting front detectors were used as indicators of groundwater pollution through nitrate leaching in the medium term. For the irrigated maize-oat rotation and dryland pasture, a low leaching risk was indicated even at high sludge loading rates of 16 Mg ha-1 in this clay loam soil. In contrast, residual nitrate for similar sludge rates under dryland maize cropping did reveal the potential for pollution through leaching. Sludge loading at all rates resulted in the accumulation of total P and loading rates of 16 Mg ha-1 increased Bray-1P in all agronomic and pasture cropping systems. In the case of turfgrass for sod production, sludge loading rates up to 67 Mg ha-1 significantly improved turfgrass establishment rate and colour. The ability of sods to remain intact during handling and transportation improved as the sludge loading rate increased to 33 Mg ha-1, but deteriorated at higher rates. A sludge loading rate of 100 Mg ha-1 was needed to eliminate soil loss at harvest, but this rate was associated with unacceptably high N leaching losses and poor sod strength. The variation in sludge quality, crop nutrient removal across a range of cropping systems, and seasons indicates that a dynamic, mechanistic decision support tool is needed to estimate responsible sludge loading rates. A mechanistic N module was adapted and incorporated into an existing soil water balance/crop growth model (SWB). The model was calibrated with statistically acceptable accuracy for dryland maize, irrigated maize-oat rotation, and dryland pasture. The model was tested against independent data sets and was able to predict the measured variables of interest with acceptable accuracy for dryland maize, irrigated maize and oats. For dryland pasture, the model predicted similar variables of interest with lower accuracy for medium-term simulations, but this improved with updating the profile water content after every hay cut. The ideal sludge loading rate to satisfy crop N demand is dynamic and should be adjusted according to cropping systems, seasonal rainfall variability, sludge N concentration, and sludge application strategy (N or P based). The ultimate cumulative sludge loading of an area will depend on the accumulation of total and Bray-1P, and the risk this poses for pollution, as long as the risk from other pollutants remains minimal. The SWB model shows promise as a decision support tool for sludge management in agricultural lands.Thesis (PhD)--University of Pretoria, 2010.Plant Production and Soil Scienceunrestricte

Modelling the soil water balance of canola Brassica napus L (Hyola 60)

Soil Water Balance (SWB) is a generic crop growth and irrigation-scheduling model. It improves on traditional methods of irrigation scheduling using evaporative demand by mechanistically and dynamically, quantitatively considering the soil–plant-atmosphere continuum. However, it needs specific crop growth parameters, which are not readily available for canola. The objective of this study was to determine crop growth parameters specific to canola and to identify the effect of water stress at different stages of growth on seed and oil yield. The study was conducted on the experimental farm of the University of Pretoria, South Africa, under a rain shelter during 2002 and in an open field during 2003. Weather data were recorded with an automatic weather station, phenological stages monitored frequently and growth analyses carried out every two weeks. Soil water content was measured with a neutron water meter weekly during 2002 and once every five days during 2003. Fractional interception of PAR was also measured with a sunfleck ceptometer. Specific crop parameters including specific leaf area, the leaf stem partitioning parameter, maximum rooting depth and thermal time requirements for crop development were generated from field measurements. These data form the backbone for accurate mechanistic simulations of the soil-water balance. The model was successfully calibrated and evaluated, proving its potential to be used as a generic crop irrigation-scheduling tool. Highest seed and oil yield was harvested from the unstressed treatment and lowest from the treatment stressed during the flowering stage.Dissertation (MSc (Agric))--University of Pretoria, 2005.Plant Production and Soil Scienceunrestricte

Yield, mineral content and root growth response of jute mallow (Corchorus olitorius L.) to planting density and water availability

Please read abstract in the article.Agricultural Research Council, Vegetable and Ornamental Plant Institute and Citrus Academy Bursary Fund.https://www.sciencedirect.com/journal/journal-of-agriculture-and-food-researchhj2023Plant Production and Soil Scienc

Implication of sludge stabilization process and polymeric material addition on nitrogen and carbon mineralization

Soil fertility deterioration has been a challenge limiting crop productivity. Recycling municipal sludge in agroecosystems proved to be an effective soil nutrient source. However, due to varied nutrient content emanating from wastewater sources and treatment processes, sludges require application rate optimization for sustainable reuse. A laboratory incubation study was conducted over 90 days to quantify carbon (C) and nitrogen (N) mineralization rate from sludge amended soils. Aerobic (AeD) sludge, anaerobic digested sludges without polymer (AnDP0) and with polymer (AnDP1) treatments were applied at 10 tons ha-1. N fractions and other parameters varied significantly with sludge treatment. AeD had significantly higher total N than AnD sludges. AeD sludge mineralized significantly higher cumulative CO2 – C than AnD. AnD sludges had higher final N mineralization rates of 43% (AnDP0) and 54% (AnDP1) against 41% from AeD sludge. Polymeric material addition increased net N mineralization rate by 10%. Cumulative mineralized N showed to be driven by the size of applied organic N pool. Applied organic N was higher in AeD relative to AnD sludges, leading to higher net N mineralized. N mineralization was faster within first 30 days of sludge application, suggesting that, for efficientmineral N utilization fromsludge, plantingmust be planned to synchronize crop N needs with this high biosolids N release period. The study showed the importance of basing sludge application rates on N content and mineralization rate rather than a single and generalized recommendation rate; a strategy that limits excess nutrient application and reducing pollution whilst enriching agroecosystems.Water Research Commission.http://www.elsevier.com/locate/crsustam2022Plant Production and Soil Scienc

Sludge stabilization process, drying depth and polymeric material addition : implication on nitrogen content, selected chemical properties and land requirement in sand drying beds

Drying beds are a simple and economical means to dewater municipal sludge and are widely used in places with a suitable climate for air-drying. However, research-based information on drying thickness/drying depth effects on nutrient content and land size requirements for sludge drying is scarce. In this study, aerobically digested (AeD), and anaerobically digested without polymer (AnDP0) and with polymer (AnDP1) sludge types were dried in sand drying beds at 5, 10, 15, 20 and 25 cm depths in South Africa. Measured nitrogen (N) fractions and other parameters were more strongly influenced by sludge types than by drying depth. Total N content followed the order of AeD > AnDP1 > AnDP0. Polymeric material addition tended to increase total and inorganic N content and reduce the length of sludge drying period and land size requirement. The study showed that larger land size is required to dry sludge at shallower depths, even though the sludge dried more quickly. Drying sludge at 15 cm was the best option across sludge types in winter, taking an average land area between 261 and 383 m2 over the fewest days of sludge drying, whereas in spring, drying at 20 to 25 cm depth was most favorable. The findings suggest that drying bed management can be based on land area requirements with little concern for biosolid quality changes. For wastewater treatment plants relying on drying in beds, adding polymeric materials may be beneficial where land area for drying beds is limited, but not otherwise. Therefore, land availability is critical in decision making for sustainable sludge drying thickness.Water Research Commission (WRC) of South Africa and EnviSafeBioC, a project financed by the Polish National Agency for Academic Exchange.http://www.mdpi.com/journal/energiespm2021Plant Production and Soil Scienc

Seasonal herbaceous structure and biomass production response to rainfall reduction and resting period in the semi-arid grassland area of South Africa

Reduction in rainfall is amongst the major climate change manifestation phenomena, and will have a significant impact on grassland ecosystems. A split plot experimental design was used to investigate the interactive effect of rainfall reduction and resting period (RP) (70 and 90 days) on herbaceous biomass production and rainwater use efficiency in semi-arid grasslands of South Africa. Different levels of rainfall reduction (RD) were setup as main plot treatments while resting periods were set as sub-plot treatments. Four 0.5 m × 0.5 m quadrats were harvested in spring, summer and autumn of 2016/17 and 2017/18 from each sub-plot to determine herbaceous species structure, aboveground biomass production and rainwater use efficiency (RUE). Grasses were most affected by rainfall reduction than forbs at the 30% and 60% RD levels. In contrast, the forbs were more affected at 15% RD while the grasses showed resilience up to 15% reduction in rainfall. The RUE was higher at 30% RD and 70 days RP in almost all three seasons, except in spring 2016/17. Our results show that herbaceous above ground biomass showed resilience up to 15% reduction but were affected more as the rainfall reduction exceeded 30%. The future predicted reduction in rainfall may result in domination of forbs and increaser grass species in the grassland.The Agricultural Research Council Center for Climate Change Collaboration (ARC-CCCC) and the National Research Foundation (NRF).http://www.mdpi.com/journal/agronomypm2021Animal and Wildlife SciencesPlant Production and Soil Scienc

Effect of irrigation with anaerobic baffled reactor effluent on Swiss chard (Beta vulgaris cicla.) yield, nutrient uptake and leaching

The disposal of treated wastewater from an anaerobic baffled reactor (ABR) effluent into water bodies can cause pollution. Treated wastewater management through irrigation of crops has the potential of increasing crop production through nutrient uptake while reducing the risks of environmental pollution. However, this study aimed to investigate the effect of irrigation with ABR effluent on Swiss chard yield, nutrient (N and P) uptake and leaching. Field experiments were done over three seasons at Newlands, Durban, South Africa. The experiments were laid out in a randomised complete block design with three treatments: ABR effluent irrigation (ABR), tap water irrigation with fertiliser (TWF) and rain-fed with fertiliser (RFF). Data were collected on nutrient (N and P) leaching at 30 and 50 cm depths, crop growth, soil chemical properties and nutrient uptake. Effects of irrigation with ABR effluent on soil chemical properties, Swiss chard growth, plant nutrient uptake and leaching were comparable to TWF and RFF treatments. This implies that irrigating crops with ABR effluent is a potential method for wastewater management in a manner that will not cause environmental pollution while benefiting peri-urban farmers.http://jwrd.iwaponline.comhb2016Plant Production and Soil Scienc

Nitrogen and phosphorus fluxes in three soils fertigated with decentralised wastewater treatment effluent to field capacity

The Decentralised Wastewater Treatment System (DEWATS) provides low cost onsite sanitation to residents living in informal settlements. Wastewater management through agriculture prevents environmental pollution and promotes sustainable agriculture. This study investigated the effects of fertigation with DEWATS effluent to field capacity in three South African soils under a banana crop. The experiment was conducted as a complete randomised design in a greenhouse with two irrigation water treatments (DEWATS effluent vs municipal tap water irrigation þ fertiliser) × three soil types (Ia, Cf and Se) and four replicates over 728 days. Data were collected on crop growth, nitrogen (N) and phosphorus (P) uptake and dynamics in the soil. The DEWATS effluent significantly (p<0.05) increased N and P uptake and soil NHþ4 -N and extractable P concentrations. Furthermore, DEWATS effluent fertigation significantly (p <0.05) increased N leaching from the Ia soil and P leaching from the Cf soil. Nitrogen and phosphorus leaching from DEWATS was lower than the tap water irrigation þ fertiliser treatment. There was, however, excess N and P accumulation from the DEWATS than the irrigation þ fertiliser treatment, which would cause environmental concerns from runoff and leaching losses in the medium to long term.The Water Research Commission, South Africahttp://jwrd.iwaponline.comam2020Plant Production and Soil Scienc

Yield decline in mechanically harvested clonal tea (Camellia sinensis (L) O. Kuntze) as influenced by changes in source/sink and radiation interception dynamics in the canopy

High labour costs and shortages and the cost of production has resulted in tea (Camellia sinensis (L)O. Kuntze) industries in central and southern Africa becoming unprofitable. This has led to the fullmechanization of shoot harvesting, however, a reduction in yield has been observed with mechani-cal harvesting. It was hypothesized that the decline in yield as a result of mechanical harvesting is aresult of the indiscriminate harvesting of shoots which leads to a change in sink/source and radiationinterception dynamics within the canopy. As a result whole plant photosynthesis is impacted; whichultimately impacts tea bush productivity. Studies conducted at Tingamira estate, Chipinge, Zimbabweshowed significant yield differences between hand plucking and machine harvesting treatments, withhigher yields under hand plucking across all seasons (43 945 kg green leaf ha−1) as compared to hand-held(35 114 kg green leaf ha−1) and ride-on machines (36 268 kg green leaf ha−1) (p < 0.05). This reduction inyield was associated with a decrease in both the number and mass of desirable shoots over each season.The cause of this change was largely attributed to the indiscriminate removal of foliage by the machineswhich resulted in the proliferation of immature shoots, with an associated increase in sink strengthand competition for available photo-assimilates. In addition, the depletion of the maintenance layer inmechanically harvested bushes, as indicated by reduced fractional interception of photosyntheticallyactive radiation in the top 10 cm in these bushes and reduced photosynthetic rates in these bushes, sug-gests that these bushes were also source limited, as compared to hand plucked bushes. Therefore thechanges in tea bush architecture, as a result of mechanical harvesting, resulted in changes in sink/sourcedynamics which led to a proliferation of immature shoots which competed for limited photo-assimilates.Tea Research Foundation of CentralAfrica for the study leave, Tanganda Tea Company, Tingamira estatefor hosting the trials and SABINA and POL/SABINA.http://www.elsevier.com/locate/scihorti2016-10-31hb201

Modelling maize grain yield and nitrate leaching from sludge-amended soils across agro-ecological zones : a case study from South Africa

When applying municipal sludge according to crop N requirements, the primary aim should be optimizing sludge application rates in order to maximize crop yield and minimize environmental impacts through nitrate leaching. Nitrate leaching and subsequent groundwater contamination is potentially one of the most important factors limiting the long-term viability of sludge application to agricultural soils. This study assessed maize grain yield and potential nitrate leaching from sludge-amended soils, using the SWB-Sci model, based on crop nitrogen requirements and inorganic fertilizer. The following hypotheses were tested using the SWB-Sci model and 20 years of measured weather data for 4 of the 6 South African agro-ecological zones. Under dryland maize cropping, grain yield and nitrate leaching from sludge-amended soils compared to inorganic fertilizer: (1) will remain the same across agro-ecological zones and sites, (2) will not vary across seasons at a specific site, and (3) will not vary across soil textures. Model simulations showed that annual maize grain yield and nitrate leaching varied significantly (P > 0.05) across the four agro-ecological zones, both for sludge-amended and inorganic fertilizer amended soils. The annual maize grain yield and nitrate leaching from sludge-amended soils were 12.6 t∙ha−1 and 32.7 kgNO3 -N∙ha−1 compared to 10.2 t∙ha−1 and 43.2 kgNO3 -N∙ha−1 for inorganic fertilizer in the super-humid zone. Similarly, maize grain yield and nitrate leaching varied significantly across seasons and soil textures for both sludge and inorganic fertilizer amended soils. However, nitrate losses were lower from sludge-amended soils (2.3–8.2%) compared to inorganic fertilizer (11.1–26.7%) across all zones in South Africa. Therefore, sludge applied according to crop N requirements has a lower environmental impact from nitrate leaching than commercial inorganic fertilizer. Further validation of these findings is recommended, using field studies, and monitoring potential P accumulation for soils that received sludge according to crop N requirements.Water Research Commission of South Africa (WRC) and East Rand Water Care Works (ERWAT).https://www.ajol.info/index.php/wsapm2020Plant Production and Soil Scienc