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Title:   Author  item
                                            LEE, SANGCHUL - University Of Marylanditem
                                            YEO, IN-YOUNG - Collaboratoritem
                                            Sadeghi, Aliitem
                                            LANG, M.W. - University Of Marylanditem
                                            McCarty, Gregoryitem
                                            HIVELY, DEAN - Us Geological Survey (USGS)
  Submitted to: PLOS ONE
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 6/3/2016
                                    Publication  Date: 6/28/2016
                                    Citation: Lee, S., Yeo, I., Sadeghi, A.M., Lang, M., Mccarty, G.W., Hively, D. 2016. Impacts of watershed characteristics and crop rotations on winter cover crop nitrate uptake capacity within agricultural watersheds in the Chesapeake Bay region. PLoS One. 11(6):e0157637.Interpretive Summary: Winter cover crops are being used as an effective agricultural practice to improve water quality in the Chesapeake Bay region, where nitrate loads into the Bay are high during the winter seasons, when cropland areas are normally left as bare.  This paper is the second of a series of follow-up papers to determine cover crop impacts on nitrate reductions, using the Soil and Water Assessment Tool (or SWAT) model.  The goal of this paper, however, was to assess the cause of difference in winter cover crop performances on the two, side-by-side sub-basins (Tuckahoe and Greensboro) within the Choptank River of the larger Bay watershed.  Although the two sub-basins are similar in size with same crop rotations, but monitoring data showed a different nitrate export patterns.  Model results were promising in providing reasonable answer for this discrepancy and showed large variation in cover crop performances in the two sub-basins studied.  This difference is most likely influenced by the soil properties of the two watersheds. Tuckahoe river basin is mostly well drained type soils while Greensboro is dominated by the poorly drained soils.  Well drained soils had expected to have higher residual nitrate in their soil profile through leaching, but poorly drained soils should have less soil nitrate, likely due to anaerobic soil condition that promotes denitrification.  Model results confirmed our observations and the validated model can be used as a decision support tool in aiding managers and decision makers for developing effective winter cover crop implementation plans suitable for local field and soil characteristics of a watershed.
                                Technical Abstract: Winter cover crops (WCCs) are gaining popularity as an effective conservation management practice to reduce agricultural nutrient loads in the Chesapeake Bay Watershed (CBW). However, WCC potential for water quality improvement has not been fully realized at the watershed scale. This study was conducted to evaluate the long-term impacts of WCCs on hydrology and nitrate loads in two adjacent watersheds, and to identify key management factors that affect the effectiveness of WCCs, using the Soil and Water Assessment Tool (SWAT). Simulation results supported the conclusion that WCCs were effective for reducing nitrate loads at the watershed scale, and their performance varied significantly based on planting date, species, soil hydrological properties, and crop rotations. Model results showed that early planted WCC outperformed late planted WCC by ~13%, and that early planted rye reduced nitrate loads by ~55%. WCCs were ~20.0% and ~5.6% more effective to reduce nitrate fluxes delivered to streams and leached into groundwater in a watershed dominated by well-drained soils than in one dominated by poorly-drained soils. Well-drained agricultural lands had higher transport of nitrate in the soil profile and groundwater, due to increased nitrate leaching. Poorly-drained agricultural lands located on extensive drainage ditches had lower soil nitrate, likely due to anaerobic soil conditions that promoted denitrification. Also, the performance of WCCs varied by crop rotation, showing increased nitrate uptake following soybean crops due to the increased soil nitrate available by the modeled mineralization of soybean residue. This study concluded that WCCs can provide an increased benefit where baseline nitrate loads are high due to increased leaching potential in well-drained soils and/or when residual and mineralized nitrate availability is high due to the cropping practices. The findings suggest that to best enhance water quality, WCC implementation plans should be established with consideration of local edaphic and agronomic chatracteristics.


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