Biochar additions to tropical soils have been shown to reduce N leaching and increase N use efficiency. No studies exist verifying reduced N leaching in field experiments on temperate agricultural soils or identifying the mechanism for N retention. Biochar derived from maize stover was applied to a maize cropping system in central New York State at rates of 0, 1, 3, 12, and 30 t ha(-1) in 2007. Secondary N fertilizer was added at 100, 90, 70, and 50 % of the recommended rate (108 kg N ha(-1)). Nitrogen fertilizer enriched with (15) N was applied in 2009 to the 0 and 12 t ha(-1) of biochar at 100 and 50 % secondary N application. Maize yield and plant N uptake did not change with biochar additions (p > 0.05; n = 3). Less N (by 82 %; p < 0.05) was lost after biochar application through leaching only at 100 % N fertilization. The reason for an observed 140 % greater retention of applied (15) N in the topsoil may have been the incorporation of added (15) N into microbial biomass which increased approximately three-fold which warrants further research. The low leaching of applied fertilizer (15) N (0.42 % of applied N; p < 0.05) and comparatively high recovery of applied (15) N in the soil (39 %) after biochar additions after one cropping season may also indicate greater overall N retention through lower gaseous or erosion N losses with biochar. Addition of biochar to fertile soil in a temperate climate did not improve crop growth or N use efficiency, but increased retention of fertilizer N in the topsoil.
