EFFECTS OF DIFFERENT PHOSPHORUS LEVELS ON UREIDES CONTENTS AND NODULATION OF SOYBEAN (Glycine max L.) IN RELATION TO SOIL MOISTURE REGIME

Soybean is a legume crop and it may fix efficiently atmospheric nitrogen (N) if an adequate amount of phosphorus (P) is present in the soil. The main product of nitrogen fixation in soybean root nodules is ureides. A greenhouse experiment was conducted on a low soil P silly clay soilsand mixture to evaluate the effect of P application and water regimes in a factorial combination on ureides contents and nodulation of soybean (Glycine max L. cv Zodiac). Soybean plants were grown in a soil very low in available P. Seeds were inoculated with bacteria Bradyrhizobium japonicum at sowing. The P application significantly increased ureides concentration and dry weights of nodules irrespective of water soil regime. In general, low amounts of ureides in nodules were found in watered plants, but those levels were significantly increased in stressed plants. Maximum dry weight of nodules and plants was obtained at 100 mg P kg soil under normal water regime of soil (70% WHC). The same trend of P influence was denoted in plants subjected to drought stress (35% WHC) but its effect was reduced by insufficiency water supply. Hence, the adequate P supply raised DM accumulation and chlorophyll contents but decreased level of ureides in roots of soybean plants. This research indicates that the ureides concentrations in plant tissues are more sensitive to P deficiency and drought than chlorophyll contents in leaves. The obtained results demonstrated that the adequate P nutrition of soybean significantly increases nodulation and ureides production in comparison to unfertilized treatment.