Predicting Phosphorus Release from Anaerobic, Alkaline, Flooded Soils

Abstract

© American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved. Anaerobic conditions induced by prolonged flooding often lead to an enhanced release of phosphorus (P) to floodwater; however, this effect is not consistent across soils. This study aimed to develop an index to predict P release potential from alkaline soils under simulated flooded conditions. Twelve unamended or manure-amended surface soils from Manitoba were analyzed for basic soil properties, Olsen P (Ols-P), Mehlich-3 extractable total P (M3PICP), Mehlich-3 extractable molybdate-reactive P (M3PMRP), water extractable P (WEP), soil P fractions, single-point P sorption capacity (P150), and Mehlich-3 extractable Ca (M3Ca), and Mg (M3Mg). Degree of P saturation (DPS) was calculated using Ols-P, M3PICPor M3PMRPas the intensity factor, and an estimated adsorption maximum based on either P150or M3Ca + M3Mg as the capacity factor. To develop the model, we used the previously reported floodwater dissolved reactive P (DRP) concentration changes during 8 wk of flooding for the same unamended and manured soils. Relative changes in floodwater DRP concentration (DRPratio), calculated as the ratio of maximum to initial DRP concentration, ranged from 2 to 15 across ten of the soils, but were ≤ 1.5 in the two soils with the greatest clay content. Partial least squares analysis indicated that DPS3 calculated using M3PICPas the intensity factor and (2 × P150) + M3PICPas the capacity factor with clay percentage can effectively predict DRPratio(r2= 0.74). Results suggest that P release from a soil to floodwater may be predicted using simple and easily measurable soil properties measured before flooding, but validation with more soils is needed.