Assessment of phosphorus status in a calcareous soil receiving long term application of chemical fertilizer and different forms of swine manures.

The continuous use of organic inputs in crop production calls for an improved understanding of how these inputs might alter soil phosphorus (P). This study assessed how the continuous application of different forms of swine manure influences the mechanism of P transformation and release potential. Soil samples were collected from a clay loam soil receiving no P or 100 kg P ha -1 applied as either chemical fertilizer (CHEM), swine liquid manure (SWL), composted swine manure (SWC) or solid swine manure (SWS) every other year for 16 years in a corn-soybean rotation. Available P increased in soils treated with P the chemical and organic fertilizers. The greatest increase was found in the SWC and SWS and was closely related to a 1% increase in the organic C content, and 1.3- and 1.2-unit increase in the soil pH for SWC and SWS treatment, respectively. Non-labile HCl-P form was also higher in SWC and SWS treated soils. Despite the similarities between SWS and SWC, SWS significantly had a lower Qmax and higher EPC O probably related to the higher organic NaOH-P. Similarly, higher organic NaOH-P together with lower CEC, Al, Ca explained the lower Qmax in SWL. This suggests that increase in organic NaOH-P forms limits the soil potential to retain P. Overall, the SWL treatment presents a unique effect on changes in soil property and P chemistry that warrants further investigation. This article is protected by copyright. All rights reserved.