Source and subsurface transport of dissolved reactive phosphorus in a semiarid, no-till catchment with complex topography

Authors: ORTEGA-PIECK, ALINE - University Of Idaho; NORBY, JESSICA - University Of Idaho; BROOKS, ERIN - University Of Idaho; STRAWN, DANIEL - University Of Idaho; CRUMP, ALEX - University Of Idaho; Huggins, David

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2020
Publication Date: 6/19/2020
Citation: Ortega-Pieck, A., Norby, J., Brooks, E., Strawn, D., Crump, A., Huggins, D.R. 2020. Source and subsurface transport of dissolved reactive phosphorus in a semiarid, no-till catchment with complex topography. Journal of Environmental Quality. https://doi.org/10.1002/jeq2.20114.
DOI: https://doi.org/10.1002/jeq2.20114

Interpretive Summary: Excessive Phosphorus in surface waters can seriously impair water quality. Sources of phosphorus include subsurface drainage lines that are in agricultural fields. Under no-tillage, movement of phosphorus in the subsurface can increase due to greater water infiltration. We found that dissolved phosphorus in subsurface drainage water was above 0.05 mg L-1 and often exceeded the water quality standard of 0.1 mg L-1 during winter. Furthermore, we determined that much of the phosphorus movement in no-till fields is from locations where soil test levels of phosphorus are high. Variable rate application of phosphorus fertilizer could minimize further enrichment of phosphorus in these locations and lead to future improvements of water quality under no-tillage. These results will be useful for farmers, NRCS and scientists interested in water quality and minimizing the potential for excess phosphorus in surface waters with no-tillage management.

Technical Abstract: The subsurface transport of dissolved reactive phosphorus (DRP) from artificially-drained agricultural fields can impair water quality, especially in no-till fields. The distribution of soil P in the wheat-dominated Palouse region in the Inland Pacific Northwest, USA varies greatly due to its steep and complex topography, and a legacy (~130 years) of excessive soil erosion and depositional processes. The primary goal of this research was to better understand the magnitude and temporal dynamics of DRP export from an artificial drain line and the variability of subsurface DRP leaching within a long-term, no-till field. DRP in drain line effluent was monitored across three water years. Large intact soil cores were extracted at contrasting field locations (toe and top slopes) to measure DRP leachate concentration and relative P sorption. Drain line DRP concentration was predominantly above 0.05 mg L-1 and often exceeded 0.1 mg L-1 during winter. Leachate DRP levels were significantly higher in toe slope cores than in top slopes cores, mainly due to a positive association with soil test P. Saturated hydraulic conductivity varied widely across cores and was not correlated with leachate DRP concentration. All soil cores exhibited high P sorption, even with preferential flows. These findings suggest that that much of the phosphorus transport in these landscapes is derived from P-enriched or hotspot areas. Variable rates of soil P fertilizer could minimize further enrichment of P in these locations.