Predicting Phosphorus Release from Anaerobic, Alkaline, Flooded Soils

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 (M3P ICP ), Mehlich‐3 extractable molybdate‐reactive P (M3P MRP ), water extractable P (WEP), soil P fractions, single‐point P sorption capacity (P 150 ), and Mehlich‐3 extractable Ca (M3Ca), and Mg (M3Mg). Degree of P saturation (DPS) was calculated using Ols‐P, M3P ICP or M3P MRP as the intensity factor, and an estimated adsorption maximum based on either P 150 or 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 (DRP ratio ), 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 M3P ICP as the intensity factor and (2 × P 150 ) + M3P ICP as the capacity factor with clay percentage can effectively predict DRP ratio ( r 2 = 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. Core Ideas Phosphorus release from flooded soils to overlying water depended on soil properties. Relative increase in floodwater DRP concentration could be predicted using the model. Clay percentage and the degree of P saturation influenced P release from flooded soils.