Edge-of-Field Water Quality in Surface and Subsurface Runoff from Paired Corn Fields.

The USDA’s edge-of-field (EoF) monitoring program is designed to quantify water quality impacts of various best management practices. We initiated an EoF study in 2014 to compare runoff and nutrient losses from two adjacent corn fields with similar soil types and identical cropping histories. The site is located in Northern NY at the Miner Institute, approximately 50 km south of Montreal, CA in the Lake Champlain Basin. The objective is to compare runoff, soluble reactive P (SRP), total P (TP), ammonium-N, nitrate-N, total N (TN) and total suspended solid loads (TSS) during a baseline monitoring period (2 yr) and following controlled drainage (CD) implementation in one field (4 yr). Both fields had tile drainage installed at 1.2 m below the soil surface in December 2014 (lateral spacing =10.7 m). Each field has a perimeter earthen clay berm and surface ditches directing surface water to flumes. Tile drain flow is routed to separate concrete manholes where it is continuously monitored and sampled via flow-based autosamplers. Tile drainage flows are estimated from curvilinear regressions based on measured flows and stage height inside of barrels equipped with v-notch weirs. Surface runoff flows to ditches and to pre-calibrated fiberglass flumes where it is gauged and sampled. Full baseline monitoring began in October 2015. Early results show total runoff losses were dominated by tile drainage in both fields (77 and 84%). Most of the SRP (89 and 92%) and TP loads (66 and 78%) were in surface runoff, whereas nitrate-N and total N losses were mainly from tile drainage (90 to 97% of total losses). Results show the importance of hydrologic flow path on N and P transport, particularly in tile-drained landscapes where P is mobilized by both surface and subsurface flows.