Effects of Biochar On Soil Physical Properties.

We established a trial in 2008 to determine the effects of biochar on crop yield and soil properties on a  Noboco-Goldsboro loamy sand (fine-loamy, siliceous, subactive, thermic Oxyaquic Paleudults) at the Williamsdale Farm Bioenergy Extension and Research Center in Wallace, NC.  In 1- by 1-m shielded microplots, five rates  of biochar  (0, 10,  20,  40, 80 dry t ha^-1)  were soil incorporated with and without N-P-K fertilizer  (147-34-34 kg N-P-K ha^-1) in a 5 X 2 factorial design in six randomized complete blocks. We produced biochar from locally obtained hardwood chips by heating in a closed chamber torrefier. The biochar was ground to pass a 5-mm sieve prior to incorporation. We established a common coastal plain 2-yr rotation (corn [Zea mays L.]–winter wheat [Triticum aestivum L.]–double-crop soybean [Glycine max L. {Merri.}]) in the microplots. Grain and total biomass were measured for each crop, and routine soil test parameters measured at the beginning and end of each rotation. In winter 2010, an undisturbed, 76-mm diameter soil core was collected from 0- to 75-mm depth in each plot. Moisture release was measured by saturating and desorbing the cores in a pressure outflow system at -1, -5, -10, -20, -30, -40, -50 kPa. After oven-drying, soil was ground to pass a 2-mm sieve, saturated, and desorbed at -100, -500, and -1500 kPa in a pressure plate apparatus. Biochar decreased soil bulk density and increased total porosity but its effect on pore size distribution and plant available water capacity (PAWC) depended on the pore size and PAWC boundary parameters used. Soil matrix and structural pore boundaries can be estimated with greater precision by analyzing the soil moisture characteristics of biochar-enriched soil, a topic we continue to explore.  Biochar improved some soil physical and chemical properties for plant growth, but to date, has had little or no effect on yield.