Biochar Application for Sustainable Crop Production, Soil and Water Quality Improvement, and Greenhouse Gas Emission Mitigation

Soil application of biochar, a product of waste biomass pyrolysis, has been shown to provide agricultural and environmental benefits. However, the exact role of biochar has been found to closely relate to the biomass source and pyrolysis condition as well as properties of the receiving soils and cropping systems. In this study, the effect of biochar on crop productivity and associated environmental influence in sugarcane and rice, two of major agroecosystems of subtropical Louisiana was evaluated in three different trials. Biochar was prepared from local-readily available sugarcane harvest residue, milling waste bagasse and rice straw. Results showed that addition of sugarcane residue biochar (SRB) and sugarcane bagasse biochar (SCBB) increased sugarcane yields by 32% and 17%, respectively. Rice straw biochar (RSBC) enhanced rice yield by 5-9% over control. In addition, SCBB reduced surface runoff loadings of phosphate-phosphorus (PO4-3-P) and nitrate-nitrogen (NO3--N) by 39 and 35%, respectively, under sugarcane cultivation. The SCBB application also reduced soil NO3--N leaching by 31-93% and lowered the loss of potassium and calcium by 24% and 74%, respectively. The RSBC decreased NO3--N in pond water of rice paddy. Biochar amendment increased global warming potential (GWP) due to higher carbon dioxide (CO2) emission, whereas the yield-scaled greenhouse gas (GHGyield) emission greatly declined. Specially, biochar application increased GWP by 5-25% compared to control, but lowered GHGyield by 7-14% under sugarcane cultivation. Biochar also significantly reduced GHGyield by 27-87% in rice paddy. Additional experiments examining alkali-enhanced biochars showed that soils amended with either potassium hydroxide-enhanced biochar (KOH-BC) or calcium oxide-enhanced biochar (CaO-BC) increased Zn sorption in both fresh and weathered samples. KOH-BC tended to decrease P sorption, whereas CaO-BC increased P sorption up to 26% and 51% in fresh and weathered samples, respectively. In addition, much of Zn adsorbed in CaO-BC amended soils was desorbed as compared to soil alone and soil + KOH-BC treatments due to differing soil pH responses. Alkali-enhanced biochars increased Zn retention as well as lability. Overall this study indicates that biochar amendments enhance crop yields, increase soil C storage and improve water quality, while minimize nutrient losses in subtropical sugarcane and rice agroecosystems