Effect of salinity on yield and nitrogen uptake of four grain legumes and on biological nitrogen contribution from the soil

Broadbean, chickpea, lentil and soybean were grown in a tank experiment and irrigated with waters of three different levels of salinity. The nitrogen uptake of the crop was determined from the yield of aereal biomass and grain, and the corresponding nitrogen contents. The biological contribution of the soil from nitrogen fixation and transformation of organic nitrogen was calculated as difference between the plant uptake and the amount supplied by fertilizer and irrigation minus the loss by drainage. Soil salinity affected crop yield, crop total nitrogen uptake and the nitrogen contribution of the soil. The latter decreased in % of plant uptake at increasing salinity and also decreased stronger than the plant uptake, pointing to a salinity effect on the mineral nitrogen production by biological activity in the soil through nitrogen fixation and transformation of organic nitrogen. A salinity effect on nitrogen fixation could explain, at least partly, the salt sensitivity of grain legumes.