Soil Chemical Properties After 50 Years of N and P Fertilization.

Nitrogen and phosphorus fertilizers were applied annually since 1961 to irrigated continuous corn and grain sorghum grown on a Ulysses silt loam in west central KS.  Treatments were a factorial of six N rates (0, 45, 89, 134, 179, and 224 kg ha^-1) and two P rates (0 and 45 kg P₂O₅ ha^-1).  Soil samples were collected in the fall of 2010 (after 50 years of fertilization) and analyzed for selected chemical properties.  In the surface soil (0-15 cm), application of N to corn decreased pH, Ca, Mg, Na, and S while increasing NO₃, Mn, and soil organic matter (SOM).  With grain sorghum, N fertilization decreased pH, Ca, Zn, and Na while increasing NO₃, Mn, and SOM in the surface soil.  For both crops, fertilizer P increased soil test P and SOM with minimal effect on other chemical properties.  Profile soil samples (300 cm depth) indicated some movement of NO₃ to 300 cm at the higher N rates with P fertilization and at lower N rates without P fertilization.