Many Kansas soils are inherently deficient in phosphorus. Cropping has also depleted the native supply of other nutrients, including nitrogen, zinc, sulfur and chloride in many areas. To produce the 22 million acres of wheat, corn, sorghum, soybeans and sunflowers harvested each year, Kansas farmers must apply fertilizer or an alternate nutrient source on most fields. In most cases, fertilizer represents the most expensive crop production input. In addition, N and P have both been identified as major contaminants of Kansas surface and/or ground water. The primary objective of the K-State Soil Fertility Research and Extension program is to provide clear and accurate recommendations for efficient, environmentally sound application of plant nutrients to cropland.