A Paired Watershed Study on Stream Water Quality from a Corn/Soybean Rotation Planted with Winter Cover Crops.

Cover crops (CCs) are being promoted as a best management practice for improving water quality through management of nutrient and sediment losses from agricultural fields. Previous studies on water quality benefits of CCs have been inferred only from plot scale studies. The objective of this research was to evaluate nitrogen, phosphorus, and sediment loss in stream water from a no-till corn/soybean rotation planted with winter cover crops (Cereal rye, Secale cereale, and hairy vetch Vicia villosa) on a watershed scale. This study was conducted in paired-watersheds under mixed land use at the Southern Illinois University Carbondale farms property from 2015 to 2017. Watershed #1 was planted with CC during the treatment period and Watershed #2 served as the control. Forty-two storm events were collected during a 4-yr calibration period and Event Mean Concentrations (EMC) for each storm event were calculated for total suspended solids (TSS), ammonia-N (NH₄-N), nitrate-N (NO₃-N), dissolve reactive phosphorus (DRP) and total discharge. Predictive regression equations developed from the calibration period were used for calculating TSS, NH₄-N, NO₃-N and DRP losses of surface runoff for CC watershed #1. The treatment period consisted of total 18 storm events, 7 of which were collected during the cereal rye and 8 in hairy vetch cover crop season. Cover crops reduced TSS and discharge by 33% and 34% in CC watershed #1 during the treatment period. However, surprisingly, EMCs for NO₃-N, NH₄-N and DRP did not decrease. Stream discharge from the paired-watersheds will continue to be monitored to determine if the current water quality results hold or new patterns emerge.