Comparison of Organic and Inorganic Phosphorus Fractions in an Established Buffer and Adjacent Production Field

Since the U.S. Department of Agriculture’s Conservation Reserve Program was established in 1985, thousands of acres of cropland have been converted to conservation buffers. The distributions of soil phosphorus (P) in various organic and inorganic fractions in a buffer and an adjacent crop production field were compared. Most of the extractable inorganic P (32 to 39%) in both the crop field and the buffer was present in the calcium (Ca)-P fraction. Levels of the most labile P fractions were higher in the cropped area; however, more P was in the iron (Fe)-P fraction in the buffer (23 vs. 18%). There were few differences among organic P fractions between the buffer and crop field. Soil sampling depth had a significant effect on the distribution of P. Differences between the cropped area and the buffer were less significant as depth increased. These results suggest that care should be taken in choosing sampling depths when relating P fraction distribution to potential P loss.