Long-Term Trends of Nitrogen and Phosphorus Use and Soil pH Change in Northern Idaho and Eastern Washington

Abstract

ABSTRACTExtension educates growers about using best management practices (BMPs) for nutrient management. However, it is important to understand grower management trends to prepare the best possible educational programs for growers. Three mail-based grower surveys conducted in 1981, 1996, and 2011 were used to document changing nitrogen (N) and phosphorus (P) fertilizer use and soil pH trends in the >450-mm precipitation zone of northern Idaho and eastern Washington, USA. The information collected in this paper spans a 40-year period. Nitrogen application rates have slightly increased, while P application rates on cereal crops have remained constant over the past 40 years. Average soil pH values have declined significantly over this time period; however, only about half of the surveyed growers were aware of this. This study is valuable because it (1) contains important information provided by growers on fertilization trends for the past 40 years (1971 to 2011), (2) quantifies the awareness of growers about soil pH decline in the region, and (3) provides baseline information, which can be used both in educational programming and to compare with future nutrient management.