Fig. 1. Extractable NH₄–N and NO₃–N for each nutrient source and application rate. At each sampling date, the NH₄–N or NO₃–N concentration in the control soil was subtracted from each sample. Means were determined to be significantly different (P 0.05) using Tukey–Kramer least square means test between N sources at each sampling date and are indicated by: z, fertilizer and digested manure; x, fertilizer and raw manure; and y, digested and raw manure.