Biochar as an Amendment to Improve Soil Fertility
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Biochar, a soil amendment resulting from pyrolysis of biomass, can improve soil texture and increase nutrient and water retention. Biochar produced from various feedstocks, each under a range of temperatures was used to amend field soil at 0.2, 0.5, 2.0, and 7.0% (w/w) application rates (equivalent to 2.6, 6.5, 26, and 91 t biochar ha-1) for growing maize in a greenhouse pot trial. Unamended controls were grown at 60, 80, 90, 100, and 140% of recommended fertilizer application rates to compare the effects of biochar against fertilizer effects. Feedstock, pyrolysis temperature, and application rate all had significant and interrelated effects on total maize biomass. In general, animal waste biochars increased biomass by up to 17%, while food waste biochar decreased biomass in relation to controls by 7 to 92%. Increasing the temperature from 300°C to 600°C decreased the negative effect of food waste biochar. The optimal application rate, regardless of feedstock or pyrolysis temperature, was 2.0% (w/w) (equivalent to about 26 t ha-1), indicating that an increased application past that point did not necessarily lead to increased yield benefits. However, several of the biochar treatments, such as poultry with sawdust and high production temperature corn stover, did lead to greater total biomass than the 140% fertilization controls. Feedstock, pyrolysis temperature and application rate deserve consideration prior to field application, as certain feedstocks can be have negative effects on yield. The initial soil environment will largely determine the interaction and impact of biochar due to varying chemical and physical qualities of biochar.
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