PREDICTING NITRATE FORMATION FROM SOIL, FERTILIZER, CROP RESIDUE, AND SLUDGE WITH THERMAL UNITS

Improved N utilization efficiency is a logical goal for reducing ground and surface water NO3- contamination associated with various agricultural practices. Providing farmers with a tool for predicting NO3- production from various N sources should allow for improved N utilization efficiency. This study was conducted to determine if soil thermal units (degree days) could be used to predict NO3- formation from unamended soils and from soils amended with inorganic N, papermill sludge, and crop residue. Fifteen studies were compiled from the literature where NO3- formation had been temporally assessed over three or more temperatures. Data were compiled from three countries, nine states, eight soil orders, 38 soil series, and 473 soil X treatment combinations. Wide ranges in NO3- concentration were found when assessed vs. days, owing to the various temperature treatments. However, this range was dramatically reduced for approximately 95% of the data files examined when NO3- concentration was plotted vs. degree days. Nitrate concentration X thermal unit relationships were found to be soil-specific, indicating this relationship should be determined for each soil or group of similar soils. Regression analyses of covariate data suggested that factors such as soil texture, pH, and climate may influence the nitrate X thermal unit relationship. Although the thermal unit approach has its limitations, its ease of calculation and demonstrated predictive capability suggest it may be a valuable tool for improving N utilization efficiency.