The Impacts of Biochar on Soil Nutrient Leaching in the Context of Extreme Hydrological Processes.

Biochar is a stable, carbon-rich material produced by pyrolysis of organic materials from plant biomass and organic wastes. Biochar has been proposed as a soil amendment for agricultural soils to enhance soil carbon sequestration, increase nutrient retention, and remediate contaminants. The physical and chemical properties of biochars are highly controlled by the characteristics of their source materials and the pyrolysis conditions. Due to its highly aromatic structure, biochar has a long mean residence time in soils relative to humified organic matter. Therefore, it is important to consider the impacts of biochar amendment under different combinations of environmental factors and human activities. Hydrological processes are a driving force in ecological systems. Extreme hydrological events caused by climate change, such as prolonged drought or frequent wet-dry cycles, could strongly influence the effects that biochar amendment has on soil ecosystem services. Our research aims to discuss the interrelationship between soil moisture history, biochar amendment, soil microbial communities, and soil nutrient leaching. A soil incubation experiment was carried out over 360 days under controlled temperature with three soil moisture treatments: simulated wet, drought, and wet-dry cycles with three biochar amendment treatments of 0, 5, 10 g biochar/kg dry soil under each of the soil moisture treatments. Walnut shell biochar, a high surface area biochar, was used in this incubation experiment. Our preliminary results show that 1) soil pH is increased by biochar amendment; 2) water-extractable dissolved organic carbon (DOC) is increased by both biochar amendment and drought and wet-dry cycle moisture treatments; 3) in the short term (30 days), biochar amendment increases soil nitrate concentrations and could therefore increase soil nitrogen losses through leaching. These results indicate that biochar has the potential to negatively impact agriculture by increasing soil nutrient leaching, particularly in the context of extreme hydrological processes. This needs to be considered further before promoting widespread application of biochar to agriculture soils.