Transport of nutrients and sediment in surface runoff in a corn silage system: paired watershed methodology and calibration period results

Authors: Jokela, William; Casler, Michael

Submitted to: Canadian Journal of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2010
Publication Date: 6/30/2011
Citation: Jokela, W.E., Casler, M.D. 2011. Transport of nutrients and sediment in surface runoff in a corn silage system: paired watershed methodology and calibration period results. Canadian Journal of Soil Science. 91:479-491.

Interpretive Summary: Eroded sediment and phosphorus and nitrogen nutrients can be transported in surface runoff from agricultural fields and may enter lakes and streams where they contribute to excessive growth of algae and aquatic weeds. We established a field study to determine how serious these nutrient runoff losses are and whether water quality can be improved by different manure and crop management. We used a “paired-watershed design” because these field-sized research units provide a more real-world landscape scale than conventional small replicated research plots. Because there is no replication with this design, first we needed a two-year calibration period to compare nutrient losses from each of the drainage areas when they all receive the same manure and crop management. This “control” management system, typical for silage corn production in the area, was fall-applied dairy manure followed by chisel plowing the same day. The calibration period ended in October 2008 and we started different management treatments on three of the drainage areas while maintaining the control system on one area. The three new management systems are: a) fall-seeded rye cover crop with spring-applied dairy manure and chisel plowing, b) fall surface-applied manure with spring chisel plowing, and c) fall manure and chisel plowing with permanent vegetative waterways/buffer strips. Statistical comparisons of runoff nutrients between pairs of drainage areas showed that good enough relationships have been established for a successful paired watershed design experiment. When the treatment phase is completed in about two years, results will help dairy farmers manage manure on their corn silage fields in a way that minimizes impacts on water quality of lakes and streams.

Technical Abstract: Transport of P, N, and sediment via runoff from crop fields, especially where manure has been applied, can contribute to degradation of surface waters, leading to eutrophication and potential health effects on humans and livestock. We used a paired-watershed design to evaluate field runoff losses of nutrients and sediment from different manure/crop/tillage management systems for silage corn production. This design employs field-scale units that reflect the real-world landscape scale better than small conventional replicated plots. This central WI site has four drainage areas or “watersheds” of about 1.5 ha each, each equipped with a 60-cm H-flume, a flow meter, and an automated 24-bottle refrigerated sampler. Samples were analyzed for suspended sediment (SS), total P (TP), dissolved reactive P (DRP), total N (TN), NO3-N, and NH4-N. During the 2-yr calibration period all watersheds were treated identically with fall dairy manure application and chisel plowing. That management was maintained as a control in one watershed, while treatments were initiated on the three other watersheds in Oct 2008: a) fall-seeded rye cover crop with spring manure and chisel plowing, b) fall surface-applied manure with spring chisel plowing, and c) fall manure and chisel plowing with permanent vegetative waterways/buffer strips. During the calibration period, nutrient and sediment loads varied by watershed, but all showed similar patterns over time. Runoff concentrations of TP and TN averaged 3 and 11 mg/L, respectively, with maximum values of 14 and 40 mg/L. Only 6% of the TP in rain-induced runoff events was in the dissolved form (DRP) compared to 37% in snowmelt runoff. Linear regressions of runoff concentrations and loads of SS, TP, and TN from paired watersheds showed good linear relationships (R2 of 0.70-0.90). Runoff losses of sediment, P, and N were relatively high, as would be expected from a low-residue corn silage system on a high-runoff soil. Regressions of runoff nutrient data for pairs of watersheds indicate adequate relationships for successful use of the paired watershed design.