SHORT-TERM EXCESS WATER IMPACT ON CORN YIELD AND NITROGEN RECOVERY

Optimum N management for soils which can have short-term, early-season periods of excessive soil water requires farmers to balance economic and environmental concerns. The objectives of this study were to evalu ate corn (Zea mays L.) yield and N fertilizer recovery following 0, 4, or 6 in. of excess soil water. Field studies were conducted from 1985 to 1988 on Cisne silt loam (fine, montmorillonitic, mesic Mollic Alba qualf), Drummer silty clay loam (fine-silty, mixed, mesic Typic Haplaq uoll), and Plainfield sand (mixed, mesic Typic Udipsamment) at three I llinois locations. Water stress was imposed by applying 0, 4, or 6 in. of water to soils at field capacity (0.33 bar). Fertilizer rates rang ed from 0 to 200 lb N/acre with an additional 50 lb N/acre being appli ed to half the plot following the water stress treatments. Isotopic N- 15 was used for the 150 lb N/acre treatment. Relative yield on Drummer decreased approximately 1% for each day soil water tension was below 0.33 bar. On Cisne, three stress days decreased yields less than 1%, b ut 7 d increased the loss to about 5%. Regression equations showed tha t even with 200 lb N/acre, 17 in. of water during May and June resulte d in yields that were only 18% of those produced with 5 in. on a Plain field sand. Fertilizer recovery averaged 88, 61, and 61% for Cisne; 83 , 50, and 44% for Drummer; and 25, 8, and 13% for Plainfield soils wit h 0, 4, and 6 in. of excess,water. Denitrification was the primary los s mechanism for the Cisne and Drummer soils, while for the Plainfield sand, it was leaching. Equations developed from this study will result in more economical and environmentally sustainable N management decis ions.