SOYBEAN NITROGEN-FIXATION AND GROWTH AS AFFECTED BY DROUGHT STRESS AND POTASSIUM FERTILIZATION

Several studies have identified drought stress as having particularly deleterious effects on symbiotic nitrogen fixation activity in soybean. Potassium is important in the growth of soybean and an important ion in the physiology of plant water relations. Therefore, this study was undertaken to examine the interactive effects of various levels of potassium and water in the soil on the nitrogen fixation activity of soybean. The experiment was done under greenhouse conditions to provide the plants with well-defined levels of potassium and to control the soil water availability. No difference in vegetative growth or acetylene reductions rates was detected among the potassium treatments. However, seed yield showed an optimum for the middle potassium treatment (50 mg K2O/kg soil) and the total accumulated nitrogen was lowest for the highest potassium treatment. As expected, dramatic differences as a result of the drought treatments were detected in nitrogen fixation rates and plant growth. Overall, there was little effect of potassium treatment on the nitrogen fixation activity of soybean under drought.