THE ROLE OF POTASSIUM FERTILIZER IN NODULATION AND NITROGEN-FIXATION OF FABA BEAN (VICIA-FABA L) PLANTS UNDER DROUGHT STRESS

Three-week-old nodulated faba bean plants were subjected to different levels of drought stress (one-half, one-quarter, or one-eighth field capacity) for 5 weeks. Half the stressed plants were treated with KCI at 10 mg kg(-1) soil or 150 mg kg(-1) soil at the beginning of the drought stress. Nodulation and nitrogenase activity were significantly decreased by increasing drought stress. Leghaemoglobin and protein contents of nodule cytosol were also severely inhibited by drought stress. This decline was attributed to the induction of protease activity. However, carbohydrate contents of the nodule cytosol increased significantly. This accumulation was attributed to a sharp decline in invertase activity and low use of sugar by the bacteroids. We conclude that harmful effects of water deficits can be alleviated by increasing K+ supplementation.