Location: Agroecosystems Management ResearchTitle: Eleven years of runoff and phosphorus losses from two fields with and without manure application, Iowa, USA
Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2016
Publication Date: 3/9/2016
Citation: Tomer, M.D., Moorman, T.B., Kovar, J.L., Cole, K.J., Nichols, D.J. 2016. Eleven years of runoff and phosphorus losses from two fields with and without manure application, Iowa, USA. Agricultural Water Management. 168:104-111.
Interpretive Summary: Monitoring runoff at field edges can show how cropping systems and conservation practices affect runoff hydrology and water quality. But because of the variable, ephemeral nature of rainfall-runoff events, multi-year studies are needed to characterize these effects. During 11 years, runoff was tracked in two Iowa fields that were in the same corn-soybean rotation, but only one field received applications of swine manure. Runoff amounts for the two fields were similar, but the manured field lost 70% more phosphorus. Large storms (>2.4 inches rainfall) only produced 12-16% of the runoff phosphorus losses, while moderate storms (1.2-2.3 inches rainfall) generated 65-70% of the phosphorus losses from both fields. Results highlight the challenge of maintaining soil P levels with manure applications while minimizing runoff P losses, and the risk of phosphorus loss that occurs when significant rains occur following manure applications. However, these challenges can be met if conservation practices can limit runoff from moderate sized (<2.4 inch) storms. These results are of interest to farmers, conservation planners, and policy makers, who are interested in knowing how extreme weather events can impact environmental performance of agricultural systems, and understanding the implications of extreme runoff events for conservation efforts that are aimed to improve agriculture's impacts on water quality.
Technical Abstract: Monitoring runoff at field edges can show how cropping systems and conservation practices affect runoff hydrology and water quality. Multi-year records are needed to measure these effects, because of the variable, ephemeral nature of rainfall-runoff events. This study compared runoff and phosphorus losses from two fields in central Iowa from 2000 through 2010. Both fields were managed in the same three-year corn-corn-soybean rotation, but one field received applications of swine manure for each year of corn. Results comprised 119 events at the manured site and 94 events at the non-manured site, with 74 events common to both locations. Rainfall-runoff relationships for the two fields were similar; annual runoff averaged 54 mm from the non-manured field and 47 mm from the manured field. Large storms (>60 mm rainfall) comprised about 10% of the runoff events in both watersheds, producing 12-16% of the total P loads. Moderate storms (30-60 mm rainfall) generated 65-70% of the P load from both watersheds. Losses of P averaged 1.8 kg P ha-1 yr-1 from the manured watershed and 1.05 kg P ha-1 yr-1 from the non-manured watershed. Relationships between runoff-volumes and phosphorus-loads differed between the two watersheds (p<0.05). Results highlight the challenge of maintaining soil P levels while minimizing runoff P losses under a corn-soybean rotation, but indicate conservation practices that can limit runoff from storms of 30-60 mm of rainfall can help producers meet that challenge.