Influence of Fertilizer, Irrigation, and Non‐Growing Season Precipitation on Soil Nitrate‐Nitrogen under Corn

Corn (Zea mays L.) production requires large amounts of N fertilizer, which may be lost due to leaching or denitrification. Prediction of the amount lost would be helpful in minimizing these losses. A field experiment was conducted to investigate the effects of fertilization, irrigation, and non‐growing season precipitation on soil NO3‐N under corn in southwestern Quebec from 1984 to 1987. The high rate of fertilization (400 kg N ha−1, 300 kg P25 ha−1, 400 kg K2O ha−1) over the normal rate (170 kg N ha−1, 100 kg P25 ha−1, 170 kg K2O ha−1) significantly increased soil NO3‐N during the growing season, and a residual effect of fertilizer rate on soil NO3‐N levels was noted in 2 of 3 yr during the non‐growing season. The high rate of fertilization, however, did not increase NO3‐N accumulation in the soil profile over the normal rate of fertilization in successive years. Irrigation significantly decreased soil NO3‐N during the growing season. At the normal rate of fertilization, gains of soil NO3‐N over winter were found with lower winter precipitation. At the high rate of fertilization, however, losses of soil NO3‐N over winter occurred in 2 of the 3 yr. The changes in NO3‐N in the rooting zone over winter depended upon the precipitation received during the preceding winter and the amount of NO3‐N in the soil the previous fall.