Phosphorus loss in surface runoff from soils with different soil test phosphorus ratings

Authors: BHATTA, A - Auburn University; PRASAD, R - Auburn University; CHAKRABORTY, D - Auburn University; Watts, Dexter; Torbert Iii, Henry

Submitted to: Agrosystems, Geosciences & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2025
Publication Date: 4/29/2025
Citation: Bhatta, A., Prasad, R., Chakraborty, D., Watts, D.B., Torbert III, H.A. 2025. Phosphorus loss in surface runoff from soils with different soil test phosphorus ratings. Agrosystems, Geosciences & Environment. 8(2):e70099. https://doi.org/10.1002/agg2.70099.
DOI: https://doi.org/10.1002/agg2.70099

Interpretive Summary: Phosphorus (P) loading from agricultural lands to water bodies through surface runoff is a major non-point source of water pollution. Farmlands containing high soil P concentrations are highly vulnerable to P loss during storm events and is of environmental concern. A study was conducted to quantify the level of P loss in runoff from soils having different routine soil test P levels. Rainfall simulations were conducted at 4 sites on a hayfield that receives swine effluent and had soil test P (STP) levels rated from "extremely high" to "very low" STP levels. Soil test using Mehlich-3 P extractant best predicted P runoff levels which indicates that Mehlich-3 can be adopted to estimate P loss from soils for environmental purposes.

Technical Abstract: Phosphorus (P) loading from agricultural lands to water bodies through surface runoff is a major non-point source of water pollution. The objective of this research was to quantify the differences in P loads in surface runoff from soils having distinct soil test P (STP) levels and determine the relationship between P concentration in runoff and routine soil test . Rainfall simulations were conducted at 4 sites on a hayfield that receives swine effluent multiple times during the year. Among the 4 sites, 1 and 2 had "extremely high" [143 mg kg-1 and 236 mg kg-1 Mehlich-1 P (M-1 P) for site 1 and 2, respectively] STP levels whereas site-3 had "high" (28 mg kg-1, M-1 P) and 4 had "very low" (5 mg kg-1, M-1 P) STP levels. Runoff samples were collected at five minutes intervals for 30 minutes post runoff generation and analyzed for dissolved reactive P (DRP) and total P (TP). Among the four sites, DRP and TP loadings during the 1st rainfall simulation at site 2 (118.4 g ha-1 and 232.3 g ha-1) were significantly higher than the other three sites. Similarly, site 2 had the highest loading for both DRP and TP (123.5 g ha-1 and 194.8 g ha-1) during the 2nd rainfall simulation. There were no statistical differences in both DRP and TP loadings between the 1st and 2nd rainfall simulation which indicates that the same amount of P loss occurs via runoff in rainfall events of similar intensity occurring within a 24 h interval. The relationship between DRP and TP concentration with STP concentrations showed a significant linear correlation. Water-soluble phosphorus (WSP) and M-3 P were better correlated with both DRP and TP which indicates that M-3 can be adopted to estimate P loss from soils for environmental purposes. These findings suggest that the soils with high STP levels are of greater environmental concern; thus, best management practices to reduce P loadings should be implemented wisely.