Nitrogen is the most important nutrient for plant growth. In cotton, the cost/benefit ratio for nitrogen fertilizer application is now believed to have reached its peak benefit stage, i.e. the point where additional nitrogen is not expected to bring proportional increases in economic returns. Most cotton areas in Argentina, Chad, Kenya, Mozambique, Paraguay, Tanzania and Uganda do not receive any fertilizer applications. This does not mean that there is no need to apply fertilizer in these countries;the reasons why they do not apply fertilizer are discussed in the article. There are only a limited number of production conditions where cotton is over-fertilized with nitrogen, and then measures are taken to avoid the imbalance between vegetative andreproductive growth. Therefore, additional increases in nitrogen doses will be beneficial only if the plant type is changed to one that can tolerate higher doses without any negative impact on yield. Fifteen cents were spent on fertilizers to produce a kilogram of lint in 1994/95 and 1997/98. By 2012/13, the cost of fertilizers had increased to 27 cents for every kilogram of lint produced. Surface application of nitrogen must be reduced in order to minimize losses. Measures to increase nitrogen use efficiency must be identified, whether by genetic, agronomic or physical means capable of improving nitrogen uptake, mobility and utilization by the cotton plant. More on nitrogen fertilizer is presented in the first article.
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