Northern Research and Demonstration Farm
A long-term experiment was established at the ISU Northern Research Farm, Kanawha, Iowa, in 1998 to study phosphorus (P) fertilization of alfalfa. Alfalfa has higher P demand than corn or soybean, and soil-test P interpretations and P fertilization guidelines in Iowa State University extension publication PM-1688 (A General Guide for Crop Nutrient and Limestone Recommendations in Iowa) are based on research more than 30 years old.
Iowa State University
Mallarino, Antonio P. and Rueber, David, "Alfalfa Hay and Soil-Test Phosphorus Responses to Long-term Phosphorus Fertilization Strategies" (2013). Iowa State Research Farm Progress Reports. 1954.