Environmental Effects of Biochars From Agricultural Wastes: Nutrient Leaching, Denitrification and Plant Growth.

Biochars made from woody biomass have been studied as a means to improve the productivity of degraded soils, especially in the humid tropics. Much less information is available for temperate soils when using biochar that was generated from a variety of agricultural and other waste streams. This presentation will focus on the environmental effects of biochar produced from a variety of organic wastes, such as paper mill wastes, food wastes, animal manures, and crop residues in comparison with better studied biomass such as soft and hard woods. Crop productivity, nitrogen leaching and nitrous oxide emissions varied significantly with different biochar types. Biochars rich in nitrogen such as poultry manure increased leaching and gaseous emissions when pyrolysed at 300C, but decreased losses when pyrolysed at 600C. The optimum application rate of biochars across a range of feedstocks was found to be about 2% by weight or about 26 t ha^-1. Some biochars were found to decrease growth of a corn test crop in a greenhouse study, such as biochar made from mixed food waste, whereas animal manures generally increased growth. Similar to nitrogen leaching, also the positive effects of the high-nutrient biochars on crop growth such as poultry manure decreased with greater pyrolysis temperature. Such analyses suggest that pyrolysis temperature may be as important as feedstock properties in determining environmental behavior of biochars. Therefore, good control over pyrolysis conditions such as temperature are critical for ensuring the environmental quality of biochars.