EFFECTIVENESS OF WINTER RYE FOR ACCUMULATING RESIDUAL FERTILIZER N FOLLOWING CORN

Excessive nitrogen fertilization rates applied to a summer annual crop and/or unusually low crop yields due to drought, can result in accumulation NO3--N in the rooting zone. The objectives of this study were to (1) measure the winter rye (Secale cereale) recovery and subsequent soil distribution of residual fertilizer N following corn (Zea mays L.) having received fertilizer N at 84, 168, 252, and 336 kg N ha-1, as N-15-depleted (NH4)2SO4, and (2) estimate potential losses of fertilizer-derived mineral N to the environment following a corn-rye rotation. Total N uptake by winter rye averaged 82 and 49 kg ha-1 in 1990 and 1991, respectively. Recovery of fertilizer N by winter rye, as measured by the isotope method, increased with increasing N rate applied to the previous corn crop and ranged from 4 to 36 kg N ha-1 in 1990 and 2 to 26 kg N ha-1 in 1991. Fertilizer recovery in 1991 was highest in rye plots where the previous corn crop bad been planted no-till (NT) into rye stubble. Little or no fertilizer derived mineral N was measured to 90-cm depth following a winter rye cover crop. In contrast, amounts of fertilizer-derived mineral N increased with depth and previous fertilizer N rate with winter fallow. These results provide evidence to support the use of a winter rye cover crop on a silt loam soil to recover residual fertilizer-derived mineral N that might otherwise be lost to groundwater