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, photosynthesis and carbon movement (using 14 C) at the V3/4 growth stages was studied in mungbean ( Vigna radiata L. Wilczek), a drought‐susceptible legume, and cowpea ( Vigna unguiculata L. Walp), a drought‐tolerant legume, grown under low‐ and high‐irrigation regimes under controlled conditions. Soil moisture and K + affected all measured parameters in the two species. The rate of photosynthesis was higher at reduced water stress when K + was applied. The impact was greater in cowpea, which had an inherently high rate of carbon assimilation. Mungbean and to a lesser extent cowpea allocated greater quantities of carbon to roots under dry conditions, especially with added K + . The distribution of 14 C into other plant parts was also increased at higher rates of K + application under both soil moisture regimes. Thus, application 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.