ARS | Publication request: Sediment and particulate phosphorus characteristics in grassed waterways from row crop corn and alfalfa fields collected using manual University of Exeter and automatic sampling

Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 3, 2011
Publication Date: July 12, 2011
Citation: Panuska, J.C., Good, L.W., Vadas, P.A., Busch, D., Ozkaynak, A. 2011. Sediment and particulate phosphorus characteristics in grassed waterways from row crop corn and alfalfa fields collected using manual University of Exeter and automatic sampling. Hydrological Processes. 25:2329-2338.

Interpretive Summary: Phosphorus (P) loss in runoff from agricultural fields can adversely impact the quality of receiving waters. Phosphorus loss occurs as dissolved P and particulate P, with particulate P often dominating loss from row crops. To identify practices to reduce P loss, land managers need good computer models and model developers need good data to improve models. Erosion and particulate P monitoring data can help identify sediment source areas and improve models, but this often requires more sediment mass than is typically obtained by more expensive automated sampling. This study used a simple suspended sediment sampler in intermittent channels draining corn and alfalfa fields and compared results with an automated sampling system. No differences were found in enrichment ratios (runoff sediment constituent/soil constituent) for sediment organic matter between the simple sampler and the automatic sampler, but the particulate P ratio from the simple sampler was 20% less than from the automatic samplers. A good correlation was found between sediment particulate P and organic matter from simple and automatic samplers for particles less than 50 µm. For particles more than 50 µm, the particulate P concentration did not change with particle size, suggesting different P enrichment mechanisms. The study provides a better understanding of particulate P transport behavior, which can help improve land use management decisions.

Technical Abstract: Phosphorus (P) export from agricultural lands above known threshold levels results in adverse impacts to receiving water quality. Phosphorus loss occurs in dissolved and sediment-bound, or particulate P (PP), forms, with the latter often dominating losses from row-cropped systems. To target practices, land managers need good computer models and model developers need good monitoring data to improve models. Sediment monitoring data can help identify sediment source areas and improve models, but often require more sediment mass than is typically obtained by automatic sampling. This study used a simple suspended sediment sampler developed at the University of Exeter (UE) in intermittent channels draining corn and alfalfa fields. The corn field had a greater runoff coefficient (27%) compared to alfalfa (11%). No differences were found in enrichment ratios (soil constituent/sediment constituent); for PP (PPER) or percent loss on ignition (LOIER) between paired UE samplers on corn. The median LOIER for the UE samplers (1.9%) did not differ significantly from the automatic sampler (2.0%); (p > 0.13). The PPER from the UE samplers was on average 20% lower than the automatic samplers. A good correlation (r2 = 0.75) was found between sediment PP and % LOI from UE and automatic samplers for particles less than 50 µm, while PP concentration more than 50 µm did not change with particle size, suggesting different P enrichment mechanisms. Sediment ammonium oxalate extraction found iron (r2 = 0.71) and magnesium (r2 = 0.70) had the highest metal - % LOI correlation. A better understanding PP behavior will improve P land use management decisions.