RESPONSE OF NITROGEN-FIXATION, NODULE ACTIVITIES, AND GROWTH TO POTASSIUM SUPPLY IN WATER-STRESSED BROAD BEAN

Three-week-old nodulated faba bean plants were subjected to two levels of water stress (0.5 and 0.25 field capacity; soil water content of 2 0 and 10%) for five weeks. Half of the stressed plants was treated wit h potassium chloride (KCI) at 10 (K1) and 150 mg (K2)/kg soil at the b eginning of water deficit. Nodulation was examined and some nodule act ivities were assayed. Nodulation, nitrogenase activity, total nitrogen (N), and dry matter yield were significantly decreased by increasing stress but were significantly higher with the two levels of potassium (K) supply. Leghaemoglobin and protein contents of cytosol as well as nodule protease and invertase were severely depressed by drought stres s. Soluble carbohydrate contents of nodules, however, was significantl y increased. Protein and leghaemoglobin contents and enzyme activities were greater with K fertilization but less soluble carbohydrate was a ccumulated. The results indicate that K supply, particularly at the 15 0 mg/kg soil level, increased faba bean resistance to water stress.