Much has been learned about the proper and judicious use of fertilizers. Fertilizer application by farmers has grown from an art to a science. As food producers have strived to increase crop yields by overcoming nutrient deficiencies the use of fertil izers has increased dramatically. This has created a large chemical industry capable of supplying the needed plant food elements. A more complete understanding of soil chemistry and plant nutrition has led to greater fertilizer use with improved fertilization methods and crop cultural practices. Improved fertilizer technology has led to the...