Introduction

The fast rate of growth in population, increasing food needs, and a widening gap between food consumption and production in the developing countries, particularly in the tropical countries of Asia, Africa, and Latin America, call attention to the need for research into those aspects of crop fertilization that have been neglected or that have the potential of affecting crop production significantly. An increase in land productivity and an expansion in the area under crops are two components of an economic strategy for increasing agricultural production. Fertilizer use is essential to this strategy because of its major contribution to crop yields, particularly in combination with irrigation and high-yielding crop varieties.