Fertilizer and Manure Management Effects on Soil Test Phosphorus after 16 Years.

The calcareous soils with low soil available phosphorus (P) common in western Minnesota make maximizing crop yields a challenge.  The objective of this project was to evaluate P management systems on crop production.  In a corn-soybean rotation, three P management factors are being examined: source (fertilizer/manure), placement (broadcast/subsurface banding), and rate (crop removal/twice crop removal).  An experimental area with initial Olsen P soil test values below 10 ppm, was initiated in 1999 in a rotation such that both crops were grown each year. P treatments were applied preceding the corn crop. After four applications, over a total of eight years, no additional P fertilizer was appied for an additional eight years. Soil test P increased with application of P over time and then declined at different rates which depended on factors such as application rate and grain yield.