Nitrate leaching from forage legume crops and residual effect on Italian ryegrass

Forage legumes can improve the N-efficiency of crop systems but also increase environmental pollution. This research investigated the NO3-N leached during the growth cycle of four forage legume crops and of barley and evaluated their residual effect on yield, N uptake and nitrate leaching of Italian ryegrass. For all crops, the nitrate leaching losses concentrated in the four months after seeding and accounted for over 78% of total N leached. On a yearly basis, nitrate leaching from legumes increased with the decrease in crop cycle length from 18 (alfalfa) to 47 kg N ha-1 (field bean). All legumes had a significant residual effect on forage and N yield of Italian ryegrass. In terms of both forage yield and nitrogen content, the beneficial effects of preceding legume crops ranked in the order: alfalfa > red clover = sulla > field bean, and was higher for N content than for dry matter.