Soil Tests as Risk Indicators for Leaching of Dissolved Phosphorus from Agricultural Soils in Ontario

Abstract

Phosphorus movement in subsurface flow from agricultural soils can be a significant pathway contributing to eutrophication of surface waters. Our study aimed to evaluate several environmental and agronomic soil P tests as indicators of dissolved reactive P (DRP) concentrations in soil-column leachate from Ontario soils. Undisturbed soil columns were collected from six major soil series, with 10 sites of each to quantitatively cover a wide range of soil test P (STP) or degree of P saturation (DPS). Split-line models described the relationships (P < 0.001) between leachate DRP concentrations and the values of In(STP) and In(DPS), with a greater slope observed above the change points than below them. Among the tested soil P measures, water-extractable P (WEP), Mehlich-3 P/(Mehlich-3 Al + Fe) (DPS^^3-1), and Mehlich-3 P/Mehlich-3 Al (DPS^,3-2) had the strongest overall relationships with leachate DRP concentration. Ontario soils were grouped into no-risk, low-risk, medium-risk, and high-risk categories based on the conditional probability of yielding leachate DRP > 0.1 mg P L"^ at a given STP as measured by WEP and Olsen P or a given DPS as measured by DPS^^j-i and DPS,^.j-2. While the Olsen P test is most commonly used for agronomic calibration in Ontario, DPS^3-2 provided the best indicator of leachate DRP concentration from Ontario soils. Regardless of the test method used, these numeric criteria could be combined with site hydrology and P management practices for a more comprehensive soil P loss assessment.Abbreviations: DPS, degree of phosphorus saturation; DPS^^,-1, Mehlich-3 phosphorus/ (Mehlich-3 aluminum + iron); DPS^¡-2, Mehlich-3 phosphorus/Mehlich-3 aluminum; DPS^3-3, Mehlich-3 phosphorus/Mehlich-3 calcium; DRR dissolved reactive phosphorus; FeO-P, iron-oxide-coated filter paper strip phosphorus; STP, soil test phosphorus; WEP, water-extractable phosphorus.

Consequences of Ontario P index recommendations for reduced manure and fertilizer phosphorus applications on corn yields and soil phosphorus

“…Ashjaei et al (2010) observed a strong correlation between labile Pi forms and leachate Pi concentrations; however, in their study, higher manure application rates were used and correlations were only significant when the soil labile Pi fractions exceeded 40 mg kg −1 . Although lower labile Pi (Resin and Bicarb) measures in the soil with reduced P inputs may be indicative of a decreased risk of soluble soil P losses in leaching waters, given the STP levels in our study and the work by Wang et al (2010Wang et al ( , 2012, the impact on soil P loss would be very small. The relatively less labile NaOH-Pi fraction was not significantly influenced by P source, rate, or P source × rate interaction (Table 3).…”

“…As a consequence, manure applications based on crop N requirements often apply P in excess of crop requirements, leading to soil P accumulation. Increased soil test P (STP) levels may indicate an increased risk of P loss through runoff and leaching, particularly when soil levels are near or exceed agronomic requirements (Wang et al 2010(Wang et al , 2012. Throughout many regions of the world, eutrophication is becoming a growing environmental concern, with agriculture identified as a major contributor of P to surface waters (Smith et al 2007;Withers et al 2014).…”

Relation between various soil phosphorus extraction methods and sorption parameters in calcareous soils with different texture

“…In many countries, recommendations for P fertilizers are based on soil test methods and recently they were also used for environmental risk assessment Sharpley et al, 2003;Daly et al, 2015). It was indicated that the P extracted by extractants such as Olsen-P and Mehlich-3-P had correlated well with P loss via runoff and/or leaching (Wang et al, 2012).…”

Phosphorus Leaching from Soil Profiles in Agricultural and Forest Lands Measured by a Cascade Extraction Method

“…However, a routine method for assessing P leaching from soil profiles is difficult to achieve because the process is time consuming and labor intensive (Heckrath et al, 1995; Hesketh and Brookes, 2000). An alternative method is to determine the leachable P content in topsoil by using H 2 O and 0.01 M CaCl 2 to evaluate the potential of P leaching from topsoil (Heckrath et al, 1995; Hesketh and Brookes, 2000; Wang et al, 2012). An indicator for P leaching based on the change‐point estimated with the split‐line model between Olsen P and leachable P has been used to predict the risk of P leaching in topsoil (Hesketh and Brookes, 2000; Zhao et al, 2007; Li et al, 2015; Jalali and Jalali, 2017).…”