Effect of soil moisture and potassium fertilizer on shoot water potential,photosynthesis and partitioning of carbon in mungbean and cowpea

The effect of different rates of potassium (K+) on shoot water potential, p hotosynthesis and carbon movement (using C-14) at the V3/4 growth stages wa s studied in mungbean (Vigna radiata L. Wilczek), a drought-susceptible leg ume, and cowpea (Vigna unguiculata L. Walp), a drought-tolerant legume, gro wn under low- and high-irrigation regimes under controlled conditions. Soil moisture and K+ affected all measured parameters in the two species. The r ate of photosynthesis was higher at reduced water stress when K+ was applie d. The impact was greater in cowpea, which had an inherently high rate of c arbon assimilation. Mungbean and to a lesser extent cowpea allocated greate r quantities of carbon to roots under dry conditions, especially with added K+. The distribution of C-14 into other plant parts was also increased at higher rates of K+ application under both soil moisture regimes. Thus, appl ication of K+ seems to have a beneficial effect in overcoming soil moisture stress and increasing physiological parameters and carbon partitioning in these two important tropical food legumes.