ABSTRACT

Cotton, like all organisms, requires nitrogen (N) for normal growth and reproduction. Few soils actually contain enough naturally occurring N to sustain high yields in most agronomic crops like cotton. Nitrogen utilization and yield response to N are greatly influenced by the availability of the N, no matter where it comes from. Inorganic N sources or organic N sources can both supply the needed N for crop production and the plant cannot distinguish between different sources. Many transformations, either biological or chemical, take place in the atmosphere, the soil, or in the plant, and are regulated by the environment and influenced by soil reaction (pH), microbial populations, N source, and many other factors. The response to fertilizer additions is variable from year to year and an understanding how different factors affect that response is critical to managing fertilizer use and efficiency. The response to fertilizers measured in experiments of similar pattern are usually consistent from year to year on soils which are either nutritionally very poor (much fertilizer is always essential) or on soils which are nutritionally very rich (fertilizer has little or no effect). Soils with intermediate fertility vary annually as a result of weather, soil conditions, cultivation, and nutrient balance.