Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/28/2004
Publication Date: 9/1/2004
Citation: Turner, B.L., Kay, M.A., Westermann, D.T. 2004. Phosphorus in surface runoff from calcareous arable soils of the semiarid western united states. Journal of Environmental Quality. 33(5):1589-1946. Interpretive Summary: Phosphorus in agricultural runoff can contribute to eutrophication of receiving water bodies. Phosphorus accumulates in soils from the application of animal manures and fertilizers. Knowing the relationships between soil phosphorus and phosphorus in the runoff will greatly facilitate our efforts to manage these systems to avoid the risks of phosphorus losses and eutrophication. We found the filterable, reactive phosphorus concentrations in the surface runoff to be related to sodium bicarbonate extractable soil phosphorus concentrations. The particulate phophorus in the runoff was related to the suspended sediment concentration. This suggests that we can use the same soil test as used for agronomic purposes to predict phosphorus runoff concentrations across a range of calcareous soils. This knowledge will allow us to predict phosphorus applications that avoid water quality problems in off-site water bodies.
Technical Abstract: Management strategies that minimize P transfer from agricultural land to water bodies are based on relationships between P concentrations in soil and runoff. This study evaluated such relationships for surface runoff generated by simulated sprinkler irrigation onto calcareous arable soils of the semiarid western United States. Irrigation was applied at 70 mm per h to plots on four soils containing a wide range of extractable P concentrations. Two irrigation events were conducted on each plot, first onto dry soil and then after 24 h onto wet soil. Particulate P (>0.45 mu) was the dominant fraction in surface runoff from all soils and was strongly correlated with suspended sediment concentration. For individual soil types, filterable reactive P (<0.45 mu) concentrations were strongly correlated wtih all soil-test P methods, including environmental tests involving extraction with water (1:10 and 1:200 soil to solution ratio), 0.01 M calcium chloride, and iron strips. However, only the Olsen-P agronomic soil-test procedure gave models that were not significantly different among soils. Soil chemical differences, including lower calcium carbonate and water-extractable Ca, higher water-extractable Fe, and higher pH, appeared to account for differences in filterable reactive P concentrations in runoff from soils with similar extractable P concentrations. It may therefore be possible to use a single agronomic test to predict filterable reactive P concentratiosn in surface runoff from calcareous soils, but inherent dangers exist in assuming a consistent response, even for one soil within a single field. Phosphorus transfer in runoff from agricultural soils to water bodies can contribute to blooms of toxin-producing cyanobacteria (blue-green algae) and other water quality problems associated with eutrophication (Foy and Withers, 1995; Leinweber et al., 2003). Accumulation of P in soils occurs following long-term application of manure or mineral fertilizer in excess of crop requirements, and a growing number of studies show strong correlations between concentrations of extractable soil P and filterable reactive P in runoff (for recent reviews see Haygarth and Jarvis, 1999; Sims et al., 2000). Linear relationships were observed in surface runoff (Pote et al., 1996, 1999), while studies of subsurface drainage under natural rainfall can display nonlinear relationships, whereby filterable reactive P concentrations increase markedly after exceeding a threshold or "change point" in extractable soil P (e.g., Hesketh and Brookes, 2000). Understanding these relationships will contribute to the development of models and management practices aimed at reducing the risk of P transfer.