Nitrogen and non nitrogen benefit of legumes to a subsequent spring barley crop

Annual legume crops in rotation with cereal contribute to nitrogen soil supply and can reduce the mineral nitrogen fertilizer demand of the following crop. The objectives of this project were to determine the nitrogen and non-nitrogen benefit of dry pea, soybean and red clover on grain yields of barley seeded the following year and their impacts on the soil nitrate. Plots of barley, dry pea, soybean and red clover were initially seeded. The following year, barley plots were established and fertilized with four rates of mineral nitrogen (0, 40, 80 and 120 kg ha(-1)). The productivity of barley increased by 13 to 50% following a legume crop compared to barley grown two-years in a row and these increments were attributed to the non-nitrogen benefit of legumes. Nitrogen benefits were estimated at 57 kg N ha(-1) for pea, 52 kg N h(-1) for soybean and 26 kg N ha(-1) for red clover. However, grain yield increments associated with the nitrogen benefit were less important than yield increments associated with the non-nitrogen benefit. Soil nitrate at harvest was higher under barley, dry pea and red clover compared with soybean. However, previous crops had no significant effect on soil nitrate in the following spring. Under these experimental conditions, nitrogen and non-nitrogen benefit associated with legumes should reduce mineral nitrogen fertilizer demand.