Characteristics.--The cowpea is closely related to the bean, and is very unlike the Canada pea, which is a true pea, thriving only in a cool climate. The cowpea has been grown in the southern states over one hundred years, and the acreage is large, but it never has come into the full use it deserves. Being a legume, it stores up nitrogen taken from the air, and unlike red clover it makes its full growth within a short period of time. It can grow on land too infertile for most kinds of valuable plants, and on better land. The vines can crowd out nearly all varieties of weeds. The roots go to a good depth and are thickly covered with the nodules of nitrogen-gathering bacteria.
Varieties.--There are many varieties of the cowpea, and confusion of names prevails, although some stations have done good service in identification of individuals carrying a number of names. The very quick-maturing varieties adapted to northern conditions do not make as much foliage as the rank-growing ones that require a relatively long season, but some of them are heavy producers of seed.
There are varieties requiring six months of southern heat to bring them to maturity, and some failures attending the introduction of the cowpea into more northern latitudes have been due to bad selection. A few varieties reach maturity within two months of hot weather.
The trailing habit is affected by the soil, the bunch varieties tending to trail when grown on fertile land. When the crop is wanted for seed, the peas that do not trail heavily will prove more satisfactory. The selection of variety is a matter of latitude and purpose, exactly as it is with corn.
Fertilizing Value.--A heavy growth of the cowpea is worth as much to the soil as a good crop of red clover. When the equivalent of two tons of hay is produced, the roots and vines contain nearly as much plant-food as the roots and first crop of medium red clover that makes two tons of hay. Some analyses show a higher percentage of protein in cowpea hay than in clover hay, and the experience of many stockmen indicates that such is the case. The roots and stubble have somewhat less fertilizing power than in the case of the clover, and all thin soils should have the entire plant, or the manure from the hay, saved without loss.