Assessing winter cover crop nutrient uptake efficiency using a water quality simulation model

摘要

Winter cover crops are an effective conservation management practice withpotential to improve water quality. Throughout the Chesapeake Bay watershed(CBW), which is located in the mid-Atlantic US, winter cover crop use hasbeen emphasized, and federal and state cost-share programs are available tofarmers to subsidize the cost of cover crop establishment. The objective ofthis study was to assess the long-term effect of planting winter cover cropsto improve water quality at the watershed scale (~ 50 km2) andto identify critical source areas of high nitrate export. Aphysically based watershed simulation model, Soil and Water Assessment Tool(SWAT), was calibrated and validated using water quality monitoring data tosimulate hydrological processes and agricultural nutrient cycling over theperiod of 1990–2000. To accurately simulate winter cover crop biomass inrelation to growing conditions, a new approach was developed to furthercalibrate plant growth parameters that control the leaf area developmentcurve using multitemporal satellite-based measurements of species-specificwinter cover crop performance. Multiple SWAT scenarios were developed toobtain baseline information on nitrate loading without winter cover cropsand to investigate how nitrate loading could change under different wintercover crop planting scenarios, including different species, planting dates,and implementation areas. The simulation results indicate that winter covercrops have a negligible impact on the water budget but significantly reducenitrate leaching to groundwater and delivery to the waterways. Withoutwinter cover crops, annual nitrate loading from agricultural lands wasapproximately 14 kg ha?1, but decreased to 4.6–10.1 kg ha?1 with cover cropsresulting in a reduction rate of 27–67% at the watershed scale. Rye wasthe most effective species, with a potential to reduce nitrate leaching byup to 93% with early planting at the field scale. Early planting ofcover crops (~ 30 days of additional growing days) wascrucial, as it lowered nitrate export by an additional ~ 2 kg ha?1when compared to late planting scenarios. The effectiveness of covercropping increased with increasing extent of cover crop implementation.Agricultural fields with well-drained soils and those that were morefrequently used to grow corn had a higher potential for nitrate leaching andexport to the waterways. This study supports the effective implementation ofcover crop programs, in part by helping to target critical pollution sourceareas for cover crop implementation.