Adequate nitrogen fertilization is needed to obtain maximum crop yields. Without sufficient nitrogen available to the plant, other inputs are wasted. There are great differences between developed and develop ing areas of the world with regard to nitrogen-fertilizer production and application, resulting in serious food deficits in some of the most needy areas. Although nitrogen fertilizer is an inexpensive input in comparison to the resulting yield increases, chemical fertilizers must be purchased and do represent a direct cash outlay, sometimes the only cash require ment for the peasant...