As the purpose of all rotation is to keep the soil productive

As the purpose of all rotation is to keep the soil productive

This crop fits in well, over wide areas, with various rotations. As the purpose of all rotation is to keep the soil productive, oats should alternate every few years with one of the nitrogen-gathering crops. In the South, cowpeas, soy beans, clovers, and vetches may be used in this rotation. In the North and West the clovers mixed with timothy hay make a useful combination for this purpose.

Source: Agriculture for Beginners