Italian Ryegrass Management Effects on Nitrogen Supply to a Subsequent Potato Crop

There is increasing use of Italian ryegrass (Lolium multiflorum Lam.) as a green manure in potato (Solanum tuberosum L.) rotations; however, effects of its management on soil N supply to the subsequent potato crop are unknown. Fertilizer N management and plow-down date for a preceding Italian ryegrass crop, 'Lemtal', on soil N supply to a subsequent potato crop, 'Russet Burbank', was determined over 2 yr. Application of N at 150 to 188 kg N ha(-1) to ryegrass increased dry matter yield and N uptake of aboveground forage and stubble (i.e., stubble, crown, and large root) tissue. Delaying plow-down from early September to early November increased dry matter yield and N uptake of stubble tissue, but not aboveground forage. Apparent recovery of applied N in harvested forage and stubble tissue averaged 55 and 12%, respectively. High N application to the ryegrass increased soil N supply to the subsequent unfertilized potato crop as indicated by increased tuber yield, mean tuber weight, and plant (i.e., vines plus tubers) dry matter yield and N uptake. However, the increase in soil N supply (i.e., N uptake of unfertilized potato plants at vine desiccation) was small (<20 kg N ha(-1)). Apparent recovery of N applied to the ryegrass crop in unfertilized potato plants was low (10%). Delayed ryegrass plow-down had no effect on soil N supply to the subsequent potato crop. Italian ryegrass green manure crop can be effective in increasing soil organic matter inputs but has limited short-term effects on soil N supply for potato.