Soil Properties, Nitrogen Status, and Switchgrass Productivity in a Biochar-Amended Silty Clay Loam

A 14-wk greenhouse study was conducted to assess how varying application rates of biomass-derived black carbon (biochar) and N fertilizer affect soil properties, plant N status, and switchgrass (Panicum virgatum L.) productivity. Biochar derived from a southern pine species was mixed with a silty clay loam at rates of 0, 0.4, 1.9, and 3.9% (w/w) and two rates of N fertilizer (0 and 56 kg ha(-1) of N as urea) were applied in a randomized complete block design. Biochar provided increases in the volumetric water content (VWC, %) of the soil during the study period. At study completion, soil pH and total C were increased. Foliar N concentration and content did not differ among treatments despite significant increases in soil C/N ratios due to biochar. Switchgrass yields were reduced at the highest biochar application rate but were unaffected when rates were moderate. Nitrogen fertilization had few effects on measured soil and plant properties, and no interactive effects were found when applied in conjunction with biochar. Overall, moderate rates of biochar application increased soil pH, soil C content, and VWC but had negligible effects on plant N status or switchgrass yields. Our results demonstrate a potential function of biochar for improving temperate soil properties.