Biochar Effects On Switchgrass Establishment and Runoff Loss of Nutrients.

Recycling of biochar, a co-product from slow pyrolysis of plant biomass, provides potential sources of mineral nutrients and organic C for sustaining biomass productivity and preserving soil and environmental quality.  Research is needed to evaluate the effects of biochar application rate on crop establishment and runoff loss of nutrients in contrasting soil textures.  Four rates of corn stover biochar (0, 4, 16, and 64 Mg ha^-1) were incorporated with and without supplemental N, P, and K fertilizer in soil within box lysimeters under greenhouse conditions.  Three replications of the eight treatments were installed in each a sandy loam and clay-textured soil.  For each soil type, simulated rainfall was applied at 50% and 100% leaf coverage of Alamo switchgrass and runoff samples were analyzed for total and dissolved N, P, and K.  For the sandy loam, 64 Mg biochar ha^-1 reduced switchgrass emergence and biomass yield at harvest compared to soil alone. In contrast, switchgrass emergence and biomass yield were similar among biochar rates in the clay-textured soil.  Follow-up greenhouse experiments in the sandy loam soil indicated reductions in seedling emergence at 64 Mg biochar ha^-1 were associated with increased salt concentration and pH (9.8) within the 2-cm depth under high light and temperature levels.  Analysis of runoff from box lysimeters indicated both biochar and fertilizer P sources contributed to increases in runoff losses of dissolved reactive P (DRP) and mass loss of total P in both soils.  Similarly, mass loss of total K was strongly influenced by increased soil concentrations of Mehlich-3 extractable K in soil amended with the high biochar rate.  A 56-day dissolution study verified that biochar was a potential source of dissolved P and other soluble mineral nutrients. If not managed carefully, biochar can adversely affect surface and groundwater quality and plant growth, especially at high application rates.