Masters Degrees (Soil Science)

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The effect of biochar application to sandy soil on nitrogen nutrition of maize (Zea mays)
(Stellenbosch : Stellenbosch University, 2023-03) Kemp, Bernitia; Rozanov, Andrei Borisivich; Hardie-Pieters, Ailsa G.; Stellenbosch University. Faculty of Agrisciences. Dept. of Soil Science.
ENGLISH ABSTRACT: Sustainable agricultural development requires a holistic systems approach to address environmental, economic, and social challenges associated with agricultural productivity. Sustainable management of sandy soil in agricultural systems requires fertilization strategies that maintain and enhance soil physio-chemical properties while sustaining optimum crop yield for the long run. Biochar production and utilization are linked directly to agriculture, the environment, and sustainable development. Biochar application is widely considered a sustainable management strategy to sequester carbon in the soil and improve soil properties. Reservations have been expressed in the literature regarding this soil amendment, particularly regarding the possible adverse effects of biochar application to soils on nitrogen nutrition of crops. A pot trial was conducted to understand the effects of biochar application on the nitrogen nutrition of maize, by investigating the impact of locally produced biochar application on the growth response (vigour) of maize and its foliar N content. This study compared the effect of biochar addition to soil with other soil amendments commonly used in agricultural systems. To clarify, this study compared biochar with compost and nitrogen fertilizer, applied independently and in combinations. Biochar was derived from black wattle pyrolyzed at 730 ° C. This study has shown that the compound application of biochar with the recommended dosage of nitrogen fertilizer had a clear positive synergistic effect on the performance of maize. This positive synergistic effect may be attributed to various improvements in soil quality typically observed in biochar-amended soils. Applying biochar had a liming effect on the acidic sandy soil when used on its own and in combination with organic/ inorganic fertilizers. The potentially mineralizable N in the soil did not differ for any treatments relative to the control. Biochar may serve as a long-term soil management strategy in agricultural systems to effectively manage nutrients, enhance the nutrient use efficiency of cropping systems, reduce N loss and subsequently limit environmental pollution, and reuse and recycle waste, while increasing agricultural production. Biochar should be designed according to the context of any given agricultural system and modified to optimally perform specific functions. Subsequently, the production and utilization of biochar will be not only efficient and profitable but also sustainable. In addition, this study emphasized that excessive N fertilization is both unnecessary and an unsustainable soil management strategy. Thus, balanced fertilization schemes may be highly beneficial for the productivity of maize cropping systems. Additional studies are required to enhance future biochar development. Especially since biochar production can significantly contribute to the sustainable development of economies, society, agricultural systems, and the environment.
Effect of biochar on chemistry, nutrient uptake and fertilizer mobility in sandy soil
(Stellenbosch : Stellenbosch University, 2012-03) Sika, Makhosazana Princess; Hardie-Pieters, Ailsa G.; Hoffman, J. E.; Stellenbosch University. Faculty of AgriSciences. Dept. of Soil Science.
ENGLISH ABSTRACT: Biochar is a carbon-rich solid material produced during pyrolysis, which is the thermal degradation of biomass under oxygen limited conditions. Biochar can be used as a soil amendment to increase the agronomic productivity of low potential soils. The aim of this study was to investigate the effect of applying locally-produced biochar on the fertility of low-nutrient holding, sandy soil from the Western Cape, and to determine the optimum biochar application level. Furthermore, this study investigates the effect of biochar on the leaching of an inorganic nitrogen fertilizer and a multi-element fertilizer from the sandy soil. The biochar used in this study was produced from pinewood sawmill waste using slow pyrolysis (450 °C). The soil used was a leached, acidic, sandy soil from Brackenfell, Western Cape. In the first study, the sandy soil mixed with five different levels of biochar (0, 0.05, 0.5, 0.5 and 10.0 % w/w) was chemically characterised. Total carbon and nitrogen, pH, CEC and plant-available nutrients and toxins were determined. The application of biochar resulted in a significant increase in soil pH, exchangeable basic cations, phosphorus and water holding capacity. A wheat pot trial using the biochar-amended soil was carried out for 12 weeks and to maturity (reached at 22 weeks). The trial was conducted with and without the addition of a water-soluble broad spectrum fertilizer. Results showed that biochar improved wheat biomass production when added at low levels. The optimum biochar application level in the wheat pot trial was 0.5 % (approximately 10 t ha-1 to a depth of 15 cm) for the fertilized treatments (21 % biomass increase), and 2.5 % (approximately 50 t ha-1 to a depth of 15 cm) for unfertilized treatments (29 % biomass increase). Since most biochars are alkaline and have a high C:N ratio, caution should be taken when applying it on poorly buffered sandy soil or without the addition of sufficient nitrogen to prevent nutrient deficiencies. In the second study, leaching columns packed with sandy soil and biochar (0, 0.5, 2.5 and 10.0 % w/w) were set up to determine the effect of biochar on inorganic nitrogen fertilizer leaching over a period of 6 weeks. It was found that biochar (0.5, 2.5, and 10.0 % w/w) significantly reduced the leaching of ammonium (12, 50 and 86 % respectively) and nitrate (26, 42 and 95 % respectively) fertilizer from the sandy soil. Moreover, biochar (0.5 %) significantly reduced the leaching of basic cations, phosphorus and certain micronutrients. This study demonstrated the potential of biochar as an amendment of acidic, sandy soils. Our findings suggest that an application rate of 10 t ha-1 should not be exceeded when applying biochar on these soils. Furthermore, biochar application can significantly reduce nutrient leaching in sandy agricultural soils.
Effect of biochar on selected soil physical properties of sandy soil with low agricultural suitability
(Stellenbosch : Stellenbosch University, 2012-03) Zeelie, Angelique; Hoffman, J. E.; Hardie-Pieters, Ailsa G.; Stellenbosch University. Faculty of AgriSciences. Dept. of Soil Science.
ENGLISH ABSTRACT: Biochar has been labelled to be a key factor in the global carbon mitigation act and has been described as the modern day equivalent (terra nova) to the terra preta dark earth soils of the Brazilian Amazon. Globally biochar has been evaluated as a means to improve soil fertility and to mitigate greenhouse gases (GHGs). Little research has however been published on the effects of biochar incorporation on soil physical properties. The objective of this study was to evaluate the effect of pine sawmill waste derived biochar (locally-produced via slow pyrolysis – 450°C) on selected soil physical properties, soil-water dynamics and crop production and- performance, when amended to a Kroonstad (Kd 1000 – Morgendal) soil form. This soil form is commonly found in the Western Cape area (South Africa) and can be classified as having low agricultural suitability for perennial- and annual crop species. Two pot trials were carried out in an atmospheric controlled greenhouse, where winter wheat and green beans respectively were planted, with five different application levels of biochar (0t/ha, 1t/ha, 10t/ha, 50t/ha and 200t/ha). Soil physical properties namely, water-stable aggregates, bulk density and water-retention capacity along with physiochemical characterisation of the sandy soil and biochar was determined. The water-use was monitored throughout the trials (evapotranspiration, volumetric water content and biomass water use efficiency, BWUE). The above- and below ground (specific leaf traits for the green bean and the root structural development for the winter wheat) biomass was collected and analysed at harvest. There was significantly higher volumetric water content measured for the 50t/ha and 200t/ha biochar treatments. This effect can be ascribed due to a change in the soil’s tortuosity and porosity where more meso- and micro-pores were present as the biochar rate increased. The same results were evident when a water-retention curve was established in vitro by means of the sandbox method. The bulk densities were only significantly lower for the 200t/ha biochar treatments. The wheat root systems differed greatly among the fertilised biochar treatments: the 50t/ha and 200t/ha treatments had a more complex fibrous root system (more extensive branching and thinner roots) than 0t/ha, 1t/ha and 10t/ha application levels. This is attributed to the increased water-holding capacity along with a reduction of N- and P availability with increasing addition of biochar. Several leaf traits were measured for the green bean crops; however the leaf nitrogen- and carbon content, chlorophyll content index (CCI) and carbon isotope fractionation yielded the most interesting findings. Concerning the fertilised biochar treatments, there was established that the 10t/ha treatments had the highest leaf nitrogen- and carbon content. The leaf chlorophyll content did not differ significantly between the fertilised biochar treatments; however a very interesting observation was evident regarding the measured leaf CCI for the unfertilised treatments. A decreasing trend and lower leaf CCI was measured as the biochar application levels increased. This effect was ascribed to be due to a decrease in N uptake by the plants as the biochar application increased, the C/N ratio also increased, and this leading to N immobilisation. The lowest leaf carbon isotope fractionation was measured for the 10t/ha fertilised treatments and is inversely correlated with BWUE and therefore endorses the conclusion that the 10t/ha biochar application had a positive effect on the long term water use efficiency for the green bean plants. Biochar promoted aggregation in the sand-rhizosphere interface for winter wheat, increased water-holding capacity and enhanced crop performance for green beans. The findings reported here provide new information on the effect of biochar on the structural development of sandy soil, combined with biochar- and root growth effects for winter wheat; along with detailed interpretations of specific leaf traits associated with crop production for commercial green beans. The addition of biochar at low application levels (approximately 1-10t/ha to 15 cm depth) increased the biomass yield and water use efficiency of the crop species. Besides long term carbon storage, biochar can have immediate positive effects on the physical properties of sand and plant growth.
The effect of composted biochar on compost properties and mineralisation
(Stellenbosch : Stellenbosch University, 2016-12) Botha, Ockert Guillaume; Hardie-Pieters, Ailsa G.; Rozanov, Andrei Borisovich; Stellenbosch University. Faculty of AgriSciences. Dept. of Soil Science.
ENGLISH ABSTRACT: Pyrolized carbon, also known as biochar, is a widely used soil conditioner recognized for its adsorption, C sequestration and agricultural qualities. This led to the investigation into the possible use thereof by small-scale sustainable farmers as a filter for agricultural olive or wine effluent, where after the spent biochar can be incorporated into composts to sterilize it from toxins and pathogens before being used as soil amendment. However, before these used biochar filters can be applied to compost, research is required to assess the affect that biochar could have on the composting process. This research project was therefore initiated to investigate the feasibility of adding biochar to composts, specifically focusing on the effect of type and amount of biochar on the composting process and mineralisation of the composts in soils. The final aim was to construct a method for quantifying biochar content in compost and soil that can be used to assess the stability of biochar in soils. Furthermore, none of this research has previously been done in South Africa or on two locally produced biochars. The first experiment was constructed to evaluate the effect of two contrasting commercial biochars on composting; a relatively low-cost, crude, pine wood biochar produced using a low-tech slow pyrolysis technique at 450°C, and a significantly more expensive, refined eucalyptus biochar produced using a high-tech slow pyrolysis technique at 900°C. The biochars were applied at two application rates (10% and 20% dry weight) to a mixture of green and animal waste. The effect was measured through composting indices such as temperature, C/N ratio, pH and EC, and microbial activity. Results showed that the robust, low temperature pine biochar applied at 10% (d/w) is the most suitable for composting due to higher composting temperatures measured, lower C/N ratios in the final product and higher cumulative microbial activity relative to the other biochar treatments. However, all biochar and control composts were all classified as successfully matured and stabilized according to the indices used, indicating that both types of biochar and application rates can be used to produce compost. The second experiment was aimed at comparing the carbon (C), nitrogen (N) and phosphorus (P) mineralisation of the composted biochar in relation to compost with biochar and biochar only under ideal laboratory conditions. The incorporation of these treatments into the soil showed that the composting process increased the composted biochars degradability with 7.6 – 11.7% more carbon dioxide (CO2) being respired than compost with biochar of the same quantity. Biochar type and quantity influenced the mineralisation as eucalyptus char in general, and all treatments containing 20% biochar proved to be least degradable by microbes. Nitrogen mineralisation results showed that regardless of biochar type, quantity or composting, all biochar containing treatments caused net N immobilization and reduced nitrification. Phosphorus availability was found to be improved for both biochars through composting and the addition of compost, especially for eucalyptus biochar of which the amount of available P surpassed that of pine biochar although pine biochar only applications released more P. A 6-month field trial experiment was also constructed to further evaluate the five composts’ C mineralisation under natural conditions. In this experiment there was found that all biochar containing compost produced 7.6 – 20.1% less CO2 than the control compost, of which eucalyptus biochar showed the least amount of respiration. Loss on ignition results also revealed that composted eucalyptus biochar was the least degradable composts as only 7.4% and 7.8% of the total SOM was lost. Density fractionation further illustrated that composted biochar remains in the soil in particulate form longer than conventional compost and is slower to transform into the mineral fraction. No discernable difference in biochar content within the composts could be seen after field application at 50 t/ha. The final aim of developing a rapid and cost-effective quantification method with the use of near-infrared spectroscopy (NIRS), was completed by constructing a calibration range of soils and compost from both types of biochar. The spectra acquired was then used to create regression models that were used to predict biochar content in the final mature composts and field trial soils. The results showed that NIRS can be used to quantify biochar, to within the same order of magnitude, in both composts and soil mixtures, which is of great importance for C stock audits and assessing biochar decay over time. Selecting the type of biochar for water filtration, composting and soil conditioning, would be dependent on the purpose of the application. Both biochars show the ability to be successfully composted and used as soil amendment with good C sequestration capabilities. However, pine biochar is more suitable for the composting process and sterilization as it results in higher temperatures and increased microbial activity. Eucalyptus biochar however, would be the best option for phosphorus mineralisation and building soil carbon stocks.
The effect of invasive alien plants (IAPs) biochar properties on soil quality and crop production
(Stellenbosch : Stellenbosch University, 2024-03) Mncedi, Sipho; Hardie-Pieters, Ailsa G.; Swanepoel, Pieter Andreas; Stellenbosch University. Faculty of Agrisciences. Dept. of Soil Science.
ENGLISH ABSTRACT: Woody invasive alien plants (IAPs), such as black wattle (Acacia mearnsii) and eucalypt (Eucalyptus camaldulensis), are a major problem in South Africa. IAPs can decrease surface water runoff and groundwater recharge and are actively being cleared on a large scale. The woody biomass generated from the clearing of IAPs can serve as feedstock for biochar production. By sequestering carbon and improving soil functions, biochar has shown promise for enhancing agricultural practices. The efficacy of biochar in enhancing soil quality and crop production varies widely depending on its properties which are influenced by the type of feedstock and pyrolysis conditions used. According to the literature, biochar can contain certain toxic compounds such as heavy metals and volatile organic compounds formed during pyrolysis. Therefore, it is critical to test biochars on intended soils and crops to select the most suitable biochars. The aim of this study was to investigate the effect of fresh and aged biochars produced from IAPs from different feedstocks and pyrolysis temperatures on soil quality and crop production. Five biochars were produced at a range of temperatures (500, 600, 700, and 800 °C) from eucalypt and a single temperature (600 °C) from black wattle biomass using low-vacuum pyrolysis. In June 2022, the biochars were applied at 1.5% (w/w) on acid sandy soil and cauliflower was cultivated in an optimally fertilized greenhouse experiment. Some of the soil-biochar mixtures were left outside for 11 months so that the biochar could age naturally in the soil. After 11 months of ageing, the cauliflower greenhouse experiment was repeated using the same cauliflower cultivar and experimental conditions. In both trials (fresh and aged biochar trial), soil chemical, physical and microbiological properties were determined at planting and harvest. At harvest, the cauliflower fresh and oven-dried curd, and above-ground biomass were determined. The oven-dried curd and leaves were analysed for total elemental macro and micronutrient analysis (N, P, S, Ca, Mg, K, Na, Fe, Mn, Cu, Zn and B). In the fresh biochar trial, the 600 °C eucalypt biochar had the most positive effect on cauliflower yields (53% increase), attributed to higher soil basic cation exchange capacity and N retention. Whereas the higher temperature (700 and 800 °C) eucalypt and 600 °C black wattle biochars suppressed crop yields by 26-79% attributed to phytotoxicity, alkalinity, and reduction of B and soil water availability. All fresh biochars were found to reduce total available water due to high microporosity. Whereas in the aged biochar trial, only low-temperature eucalypt biochar (500 °C) suppressed the total available water. Biochar ageing reduced soil total N, but slightly increased effective cation exchange capacity and easily available water content however not compared to the aged sand control. The ageing of eucalypt and black wattle biochar also seemed to reduce the phytotoxicity that was present in certain fresh biochars. However, none of the aged biochars had a significant effect on cauliflower yields compared to the control sand. The results of this study highlight the importance of biochar properties, as influenced by pyrolysis conditions and feedstock, on crop growth response.

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