Nutrient Management for Increased Crop Productivity and Reduced Environmental Impacts

Careful management of plant nutrients is more important than ever because of volatile grain/fertilizer price ratios and public concerns about water quality impairment due to excess nutrient loss from fields. The management concepts most relevant to increase the efficacy of crop production while limiting water quality impairment are different for nitrogen (N) than for less mobile nutrients such as phosphorus (P) and potassium (K). This article highlights considerations for P and K but with emphasis on P because deficiencies are more widespread and excess P loss results in serious water quality impairment. Soil testing, nutrient removal with crop harvest, and soil chemical/mineralogical properties are important pieces of information that must be used together with price ratios when deciding P and K application rates. Soils of some regions can retain or transform significant amounts of applied P and K in forms of low availability for crops. In most regions, however, P or K retention by soil does not mean much "fixation", which allows for management of fertilization over time. For example, an excess P or K applied for a first crop in a rotation does not necessarily imply a yield or economic loss because it will be crop-available next year. The possibility for long-term management and consideration of the probability of a crop response for different soil-test values result in several options concerning soil-test interpretations and fertilizer application rates and timing. Other considerations should include land tenure and producers’ attitude concerning economic risk, and potential impacts on water quality, which expand the realm of management options. These issues must be considered when making fertilization decisions because they result in different “best management practices”. Many prefer simple science-based recommendations, but an oversimplification of recommendations will not result in better nutrient management, more profitable crop production, or improved water quality. This presentation will address some of these issues based on the Iowa experience in a way that may be useful to scientists, crop consultants, and producers in regions where production conditions may be similar or different. † Proceedings (English version), Joint XIX Latin American and XXIII Argentinean Soil Science Congress. Mar del Plata, Argentina, 16 20 April, 2012. ‡ Professor. 3216 Agronomy Hall, Department of Agronomy, Iowa State University. Ames, IA 50011.