Growth and forage yield of cowpea and mungbean in the northern Great Plains

Cowpea [Vigna unguiculata (L.) Walp.] and mungbean [Vigna radiata (L.) Wilczek] are summer-annual legumes which have potential as forages in the northern Great Plains region of the USA during late summer when cool-season grass pastures decline in productivity. The objective of this study was to evaluate forage yield and growth response of these species when grown under different row spacings and planting rates. Victor cowpea and Berken mungbean were planted at 500 000 pure live seeds (PLS) ha−1 in row spacings of 25, 50, and 75 cm at two South Dakota locations in 1987. In 1988 the two species were planted at rates of either 250 000 or 500 000 PLS ha−1 in the same row spacings at three locations. Cowpea produced higher forage yields than mungbean at all locations in both years. Yields of both species decreased with increased row spacing. Species did not differ in plant weight, but plant number per unit of harvested area was greater for cowpea than mungbean. Forage yield was not significantly affected by planting rate at any location in 1988; however, plant weight, leaflets plant−1, and leaf area plant−1 were significantly greater for the low rate, showing that forage yield remained relatively constant across wide variations in plant population. Results indicate that both cowpea and mungbean have potential as summer annual forage crops. However, the consistently higher yield performance of the cowpea cultivar suggests that it was better adapted than the mungbean cultivar to the northern Great Plains region and consequently should be a better forage crop. Key words: Vigna unguiculata (L.) Walp., Vigna radiata (L.) Wilczek, yield, plant density, cowpea, mungbean