Environmental Index for Estimating the Risk of Phosphorus Loss in Calcareous Soils of Manitoba

Abstract

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 (ES(max)) ranged from 0.5 to 31.9% while those obtained from P(Ols) and the single-point adsorption index (P(150)) ranged from 0.9 to 73.9%. Of all the DPS evaluated, those that included P(Ols) and Mehlich 3-extractable ((M3)) P as the numerator with either P(150) or ES(max) as the denominator were fairly well correlated with P(H2O) (r values ranged between 0.45 and 0.63). Along with ES(max) and P(150), a new method of calculating DPS was formulated as the ratio of P(Ols) or P(M3) to Ca(M3) 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, Ca(M3) or (Ca + Mg)(M3) were better indices of P sorption capacity while P(Ols) and P(M3) provided better estimates of labile soil P. The DPS calculated using Ca(M3) or (Ca + Mg)(M3) were well correlated with P(H2O); however, they were numerically smaller than those obtained from the Langmuir adsorption maximum. As such, a saturation coefficient (alpha) 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.

Degree of phosphorus saturation threshold for minimizing P losses by runoff in cropland soils of Southern Brazil

“…There is a lack, however, of studies regarding the assessment of P losses by surface runoff in these soils. In the present study, it is expected that the DPS, successfully tested in other regions of the world, might be suitable to estimate the risk of those losses in soils of Southern Brazil (Ige et al, 2005;Casson et al, 2006;Guérin et al, 2007;Wang et al, 2009).…”

“…A P sorption coefficient, α, is applied to compare the different DPS estimates (Ige et al, 2005). However, α values can vary widely (Ige et al, 2005) and, for this reason, an increasing number of researchers are not using it anymore (Vaughan et al, 2007).…”

“…However, α values can vary widely (Ige et al, 2005) and, for this reason, an increasing number of researchers are not using it anymore (Vaughan et al, 2007). Ammonium oxalate is the major extractor used to calculate the DPS.…”

“…The PI is the most widely used index throughout the world (Bechmann et al, 2009;Nelson & Shober, 2012). However, the simple soil test P (STP) (Pote et al, 1996;Nelson & Shober, 2012), the P sorption index (PSI) (Sims, 2009), and the degree of P saturation (DPS) (Ige et al, 2005) have also been successfully used for this purpose.…”

“…The DPS can be calculated in many ways, based on the STP of a specific region and on the different forms to obtain PSC (Ige et al, 2005;Verbree et al, 2010). Wang et al (2009), for example, used the STP and PSC estimated both by Mehlich-3 extractable Al and Fe+Al to calculate the DPS in soils of Ontario.…”