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ARS Home » Midwest Area » Bowling Green, Kentucky » Food Animal Environmental Systems Research » Research » Publications at this Location » Publication #358821
Research Project: Developing Safe, Efficient and Environmentally Sound Management Practices for the Use of Animal Manure

Location: Food Animal Environmental Systems Research

Title: Evaluating the potential for calculating the degree of P saturation from ammonium lactate extractable Al, Fe, and P

Author
item Bolster, Carl
item BLOMBACK, KARIN - Swedish University Of Agricultural Sciences
item HESSE, KATHRIN - Swedish University Of Agricultural Sciences
item LINDSJO, ANDERS - Swedish University Of Agricultural Sciences
item LINEFUR, HELENA - Swedish University Of Agricultural Sciences

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 12/7/2018
Publication Date: 6/30/2019
Citation: Bolster, C.H., Blomback, K., Hesse, K., Lindsjo, A., Linefur, H. 2019. Evaluating the potential for calculating the degree of P saturation from ammonium lactate extractable Al, Fe, and P. Meeting Abstract. Paper No. 87.

Interpretive Summary:

Technical Abstract: The degree of P saturation (DPS) – originally defined as the molar ratio of acid ammonium oxalate (OX) extractable P to Al and Fe – has been shown to be a good predictor of a soil’s risk of releasing P in runoff or leaching water. Because ammonium oxalate extraction is not commonly used in routine soil tests, researchers have investigated whether calculating DPS from P, Al, and Fe concentrations obtained from routine soil extracts can be used in lieu of DPSOX. In Sweden, ammonium lactate (AL) is the extract routinely used for determining soil P concentrations. In this study, we investigated the correlation between DPS values calculated from ammonium lactate and ammonium oxalate extract data from topsoil sampled from 62 different arable fields in Sweden. We also conducted P sorption isotherms on a subset of 11 of these soils to calculate the P sorption maximum using the Langmuir equation. We observed relatively mild, yet statistically significant (p < 0.05), correlations between AL- and OX-extracted Al, Fe, and P concentrations with r values of 0.66, 0.54 and 0.53, respectively. Ammonium oxalate extracted greater concentrations of Al, Fe, and P than ammonium lactate by an average factor of 5.5, 12, and 7, respectively. Ammonium lactate extracted proportionately less Fe than Al compared with the oxalate extractions with the ratio of FeOX to PSCOX ranging from 27 to 75% (mean of 53%) whereas the ratio of FeAL to PSCAL ranged from 8.5 to 61 % (mean of 38%). There was a relatively poor correlation between the P sorption capacity (PSC) – defined as the sum of extractable Al and Fe – for the two extractions indicating that these two methods are extracting different pools of Fe and Al. PSCOX values ranged from 2.9 to 19.9 (median of 7.2) times greater than PSCAL. Unlike PSC, a strong relationship was observed between DPSOX and DPSAL (r = 0.84). While we observed a strong relationship between the Langmuir maximum sorption coefficient (Smax) and PSCOX for a subset of 11 soils, the correlation between Smax and PSCAL was not statistically significant. Both DPSOX and DPSAL were strongly correlated with water- and CaCl2-extractable P with r values of 0.82 and 0.84 for DPSOX and 0.88 and 0.85 for DPSAL, respectively. We did not observe any change point in water- or CaCl2-extractable P concentrations as a function of DPS.