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ARS Home » Midwest Area » West Lafayette, Indiana » National Soil Erosion Research Laboratory » Research » Publications at this Location » Publication #410016
Research Project: Assessment of Sediment and Chemical Transport Processes for Developing and Improving Agricultural Conservation Practices

Location: National Soil Erosion Research Laboratory

Title: Accumulation of soil phosphorus within closed depressions of a drained agricultural watershed

Author
item MUMBI, ROSE - Purdue University
item Williams, Mark
item Penn, Chad
item CAMBERTO, JAMES - Purdue University

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2024
Publication Date: 4/16/2024
Citation: Mumbi, R., Williams, M.R., Penn, C.J., Camberto, J.J. 2024. Accumulation of soil phosphorus within closed depressions of a drained agricultural watershed. Soil Science Society of America Journal. https://doi.org/10.1002/saj2.20671.
DOI: https://doi.org/10.1002/saj2.20671

Interpretive Summary: Closed depressions or 'potholes' are common across the U.S. Midwest and globally. In this study, we examined the spatial patterns of soil phosphorus (P) within a agricultural watershed with closed depressions. We hypothesized that erosion and runoff from the depression hillslopes may result in P accumulation near the bottom of the depression, which then may be at risk of loss either through tile drainage or a surface inlet. We sampled soil from 14 agricultural depressions and 5 forested depressions from 0 to 24 inches deep and analyzed the samples for P concentration. Results showed that soil P concentration was 2 to 10 times greater in the depression bottom compared to the hillslope contributing area across all depths. Long-term management practices such as P application history and tillage influenced the magnitude of soil P accumulation. Findings indicate that closed depressions may act as hotspots for P cycling and loss. Including low-lying depressional areas as part of a routine soil sampling strategy combined with variable rate P application could lessen P accumulation and potentially reduce P losses.

Technical Abstract: Closed depressions are common landscape features across glaciated landscapes. Erosion and runoff from depression hillslopes may result in phosphorus (P) accumulation near the bottom of the depression, with this ‘legacy P’ potentially at risk of loss to surface waters when drained via tile drainage. We assessed the spatial patterns of soil P within a tile-drained watershed as a function of landscape position, land use, and agricultural management practices. Paired soil samples (depression bottom vs. hillslope contributing area) were collected from agricultural (n=14) and forested (n=5) depressions at four depths 0 to 60 cm. Water-extractable P (WEP), Mehlich-3 P (M3-P), total P (TP), Hedley P fractions, and other physical and chemical characteristics were determined. To assess the risk of P loss, P desorption from surface soils (0-5 cm) was quantified using flow-through experiments. WEP, M3-P, and TP were two to ten times greater in the depression bottom compared to hillslopes across all depths. Agricultural depressions had greater soil P concentration compared to forested depressions, with long-term management practices such as P application history and tillage influencing the magnitude and vertical stratification of soil P. Flow-through experiments highlighted that the risk of P loss was highly dependent on M3-P concentration for both hillslope and depression soils. Findings therefore indicate that closed depressions may act as hotspots for P cycling and loss in tile-drained watersheds. Including low-lying depressional areas as part of a routine soil sampling strategy combined with variable rate P application could lessen P accumulation in depressions and reduce P loading to surface waters.