Developing Credible Models to Adapt Crop Nutrient Management to Weather.

Over the course of many decades, agronomists have done extensive research to develop nutrient recommendations for specific crops in specific regions. For nitrogen (N), this research supports adjustments for factors including previous crop, application timing, price ratio, yield goal, previous crop and soil texture. For phosphorus (P), the main factor is usually the soil test. The science supporting such recommendations usually explains no more than one-third of the variability in optimum rates observed across field experimental sites. A considerable portion of the remaining variability could be due to weather. Temperature and moisture affect many processes in the soil-crop system known to influence optimum N rates. Rainfall timing and soil properties affect loss of applied P in surface runoff. The complexity of the interactions of these processes warrants the use of past, current and forecast weather information in soil-crop system models to improve nutrient application decisions. A science-based approach to developing such models will cross many disciplinary boundaries, including those of agrometeorology, soil physics, chemistry, and plant physiology. In addition, the development and dissemination of such decision support requires a large effort to validate the models. This effort requires on-farm testing as part of an adaptive management approach, in order to build the users’ confidence in the models and to provide feedback to scientists for model improvement. The results of such on-farm validation can also be aggregated and communicated to consumers and the public as performance indicators. A combined program of weather-based model development and on-farm adaptive research can serve to enhance confidence in all stakeholders by relating nutrient stewardship efforts to the improvement of the sustainability of agriculture.