Predicting Soil Phosphorus Sorption Capacity (PSC) for Manure and Biosolid Amended Soils of the Inner and Outer Bluegrass Regions in Kentucky.

Predicting Soil Phosphorus Sorption Capacity (PSC) for Manure and Biosolid Amended Soils of the Inner and Outer Bluegrass Regions in Kentucky

K.K. Meier, A.D. Karathanasis, and Y. L. Thompson

It is well established that increased P saturation of agricultural soils is associated with P enrichment and potential eutrophication of fresh waters. Compared to typical Kentucky soils, Inner and Outer Bluegrass region soils have a higher than average soil test P. Establishing a relationship between soil test P levels and potential P losses can improve P amendment recommendations and minimize negative environmental impacts. Two soils from the Outer Bluegrass and two from the Inner Bluegrass region of Kentucky, with soil test P values ranging from 48 to 485 mg/kg, were selected as representative agricultural soils. These selected sites had no recent history of organic P amendment applications. Surface soil samples, air dried, and ground to pass a 2mm sieve, were amended with cattle manure, horse manure, and a municipal biosolid for 108 days at 25^oC. Incubated samples were collected at 0, 3, 7, 14, 28, 58, and 108 days to determine the effect of amendment additions to inorganic P and PSC over time.  Soil PSC was measured using a batch isotherm approach to determine a sorption maximum from the Langmuir equation.  The measured PSC values were related to phosphorus sorption index (PSI) estimates derived from single point P sorption measurements and from Mehlich 3 extractions of P, Al, and Fe. Integrating current soil test methods with reliable estimates of fluctuations in the liable soil P pools could greatly improve soil management recommendations for waste applications.