Nutrient Leaching and Retention in Riparian Soils as Influenced by Rice Husk Biochar Addition

Biochar application to agricultural soils has been reported to reduce nutrient leaching and ameliorate degraded soils. However, few studies exist that verify decreased nutrient leaching in biochar-amended riparian soils or that identify the mechanism for nutrient retention. Column leaching experiments were conducted to investigate the effects on nutrient leaching and retention of rice husk biochar additions at varying rates (0%, 1%, 2%, 5%, and 10% by weight) following application of fertilizer (NH4NO3 and KH2PO4) to a subtropical riparian soil from the Taihu Lake watershed of China over a 24-week incubation. We found that increasing levels of biochar decreased cumulative amounts of leachate NH4+-N by 28 to 63%, NO3--N by 23% to 84% and dissolved organic nitrogen by 15% to 46%, while increasing leaching of PO4+-P by 43% to 108%. Total nitrogen (N) and available phosphorus (P) contents significantly increased in the biochar-amended soil. The significant increase in soil microbial biomass N after biochar addition suggests that fertilizer N was retained by microbial cycling. The decrease in NH4+-N and increase in NO3--N in biochar-amended soil imply that nitrification was enhanced with biochar addition. Biochar treatments increased soil available P due either to the release of soluble P frombiochar or to enhanced P mineralization by soil microbial biomass. These results indicate that addition of biochar increased the capacity of the riparian soil studied to provide plant available nutrients and reduce N leaching.