Environmental Index for Estimating the Risk of Phosphorus Loss in Calcareous Soils of Manitoba
- D. V. Ige,
- O. O. Akinremi * and
- D. N. Flaten
The degree of phosphorus saturation (DPS) has been used in evaluating the risk of P loss from soil to runoff. While techniques are available for calculating DPS for acid soils, no widely used technique exists for neutral to calcareous soils that are typical of the Northern Great Plains, including Manitoba (Canada) soils. This study aimed to develop techniques of calculating the DPS of neutral to alkaline soils. Four measures of soil labile P and ten indices of P sorption capacity were used to calculate the DPS of 115 Manitoba soils. The various DPS calculated were evaluated using water-extractable (H2O) P as an index of P susceptibility to runoff loss. The DPS obtained using Olsen-extractable (Ols) P and the Langmuir adsorption maximum (ESmax) ranged from 0.5 to 31.9% while those obtained from POls and the single-point adsorption index (P150) ranged from 0.9 to 73.9%. Of all the DPS evaluated, those that included POls and Mehlich 3–extractable (M3) P as the numerator with either P150 or ESmax as the denominator were fairly well correlated with PH2O (r values ranged between 0.45 and 0.63). Along with ESmax and P150, a new method of calculating DPS was formulated as the ratio of POls or PM3 to CaM3 or (Ca + Mg)M3 We found that the ratio of ammonium oxalate–extractable (ox) P to (Al + Fe)ox, which has been widely used to calculate DPS in acid soils, was not suitable for neutral to alkaline soils of Manitoba. In these neutral to alkaline soils, CaM3 or (Ca + Mg)M3 were better indices of P sorption capacity while POls and PM3 provided better estimates of labile soil P. The DPS calculated using CaM3 or (Ca + Mg)M3 were well correlated with PH2O; however, they were numerically smaller than those obtained from the Langmuir adsorption maximum. As such, a saturation coefficient (α) with a value of 0.2 was generated to improve the numerical values of the newly estimated DPS. This new approach can be used to estimate the DPS in neutral and calcareous soils without the need to generate a P adsorption maximum.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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