Effect of Legumes on Soil Mineral Nitrogen and Response of Potatoes to Nitrogen Fertilizer

Abstract

In a long-term field trial red clover and lucerne were grown once every four years as a main crop and could be regarded as green fallow crops. When the legumes were grown, oats were grown as a reference crop. The effect of the legumes on nitrogen fertilizer requirement and yield of the subsequent potato crops was studied. To obtain an estimate of the amount of nitrate which may be leached, the study included measurements of soil mineral nitrogen. Beneficial effects of growing red clover and lucerne compared with oats were a substantially lower nitrogen fertilizer requirement of the subsequent potato crop (67-99 kg N per ha) and much higher tuber yields without nitrogen fertilizer application (up to 15 t/ha). Adverse effects, however, were somewhat lower tuber yield with the optimum application rate of nitrogen fertilizer and probably heavier leaching losses in the long run. With respect to nitrate leaching it is concluded that legumes should be used with caution as green fallow crops.