Total soil N and C of the 55 samples were measured with a Carlo-Erba NA1500 Analyzer. The % black soil in each sample was estimated as: (M - S)/(B - S) x 100, where M = total N of the sample, S = total N of pure sand, and B = total N of pure black soil. The 11 experimental plots were divided into 5 soil mixture levels based on the % black soil they contained: level 1 contained 0 to 15% black soil, level 2 contained 20 to 40% black soil, level 3 contained 50 to 75% black soil, level 4 contained 75 to 100% black soil and level 5 contained 100% black soil and was fertilized monthly with NH4NO3. Levels 1 and 2 each included 3 plots, levels 3 and 4 each included 2 plots and level 5 included a single plot.