Impact of biochar on nitrate accumulation in an alkaline soil

The effects of biochar on alkaline soils in high-yielding agricultural fields remain poorly understood. Nitrate variation in soils due to biochar application without a change in soil pH, is a great concern relating to both crop yield and nitrate leaching. In this study, we monitored changes in dynamics of soil nitrate accumulation and effects on grain yield due to biochar application in a temperate, high-yielding region. Biochar derived from corncob was applied to an alkaline soil at biochar rates (kg ha(-1)) of 0 (CK), 2250 (C1), and 4500 (C2) for each of two crop seasons in 2007. A treatment with 750kg biochar-based fertiliser ha(-1) (CN) for each of two crop seasons was also included. Biochar had no significant effect on soil water content to 1m soil depth. Biochar tended to increase the soil cation exchange capacity (CEC) in the 0-20cm soil layer and nitrate retention to 1m soil profile, but there was no significant difference between biochar treatments and CK. Grain yield of C1, C2, and CN was improved by 10.3%, 16.9%, and 15.5% compared with CK, respectively, but only C2 was significantly different from CK. Grain yields of winter wheat with biochar application showed a trend similar to soil CEC and average soil-nitrate retention, suggesting that the increases in grain yield were mainly attributable to improvements in soil CEC and soil nitrate retention due to biochar application in the alkaline soil. In conclusion, the effects of biochar on soil water retention, soil nitrate retention, and grain yield were very limited in alkaline soil in a high-yielding region.