Influence of Soil Moisture and Fertilizer Potassium on the Vegetative Growth of Mungbean (Vigna radiata L. Wilczek) and Cowpea (Vigna unguiculata L. Walp)

Tropical food legumes are grown in a wide range of environments, and water stress is considered the principal environmental factor limiting growth and yield. Potassium fertilizer mitigates the impact of water stress in plants. However, the benefits of potassium in overcoming stress in tropical food legumes have not been investigated in comparative studies. The purpose of this study was to determine the benefits of potassium in overcoming water stress in mungbean and cowpea, two important tropical food legumes with different adaptabilities to soil moisture regimes. The experiment carried out under controlled conditions placed emphasis on vegetative growth and selected physiological parameters. The impact of potassium was different in the two legumes grown at optimal and suboptimal soil moisture. Potassium increased shoot growth of mungbean to a greater extent than in cowpea under suboptimal moisture conditions. The roots of cowpea showed a greater response to potassium fertilizer than in mungbean under suboptimal soil moisture. The plant water relations and photosynthetic rates of mungbean were improved to a greater extent by potassium under suboptimal soil moisture than those of cowpea. Although differences were observed in the responses of the vegetative growth of these species to moisture and potassium, in overall terms potassium promoted growth of both species when subject to suboptimal soil moisture. While field studies are required to validate the results, the application of potassium fertilizer can be considered a significant factor in overcoming soil moisture stress in these legumes commonly grown in tropical cropping systems.