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

Abstract

Abstract. Winter cover crops are an effective conservation management practice with potential to improve water quality. Throughout the Chesapeake Bay watershed (CBW), which is located in the mid-Atlantic US, winter cover crop use has been emphasized, and federal and state cost-share programs are available to farmers to subsidize the cost of cover crop establishment. The objective of this study was to assess the long-term effect of planting winter cover crops to improve water quality at the watershed scale (∼ 50 km 2 ) and to identify critical source areas of high nitrate export. A physically based watershed simulation model, Soil and Water Assessment Tool (SWAT), was calibrated and validated using water quality monitoring data to simulate hydrological processes and agricultural nutrient cycling over the period of 1990-2000. To accurately simulate winter cover crop biomass in relation to growing conditions, a new approach was developed to further calibrate plant growth parameters that control the leaf area development curve using multitemporal satellitebased measurements of species-specific winter cover crop performance. Multiple SWAT scenarios were developed to obtain baseline information on nitrate loading without winter cover crops and to investigate how nitrate loading could change under different winter cover crop planting scenarios, including different species, planting dates, and implementation areas. The simulation results indicate that winter cover crops have a negligible impact on the water budget but significantly reduce nitrate leaching to groundwater and delivery to the waterways. Without winter cover crops, annual nitrate loading from agricultural lands was approximately 14 kg ha −1 , but decreased to 4.6-10.1 kg ha −1 with cover crops resulting in a reduction rate of 27-67 % at the watershed scale. Rye was the most effective species, with a potential to reduce nitrate leaching by up to 93 % with early planting at the field scale. Early planting of cover crops (∼ 30 days of additional growing days) was crucial, as it lowered nitrate export by an additional ∼ 2 kg ha −1 when compared to late planting scenarios. The effectiveness of cover cropping increased with increasing extent of cover crop implementation. Agricultural fields with well-drained soils and those that were more frequently used to grow corn had a higher potential for nitrate leaching and export to the waterways. This study supports the effective implementation of cover crop programs, in part by helping to target critical pollution source areas for cover crop implementation.

Assessing the Impacts of Future Climate Conditions on the Effectiveness of Winter Cover Crops in Reducing Nitrate Loads into the Chesapeake Bay Watersheds Using the SWAT Model

“…The WCC biomass simulated using the parameters from Yeo et al (2014) was consistent with field observations conducted at different periods in this region . Therefore, we used the calibrated WCC biomass growth parameters provided by Yeo et al (2014). In addition, we set the base and optimal temperatures for the three WCC species (i.e., rye, barley, and wheat) as 4°C and 18°C, respectively, based on literature and local knowledge (Feyereisen et al, 2006;Prabhakara et al, 2015).…”

“…Yeo et al (2014) estimated WCC parameters that represent the typical growth patterns of rye, barley, and wheat for this region based on landscape-level observed biomass reported by Hively et al (2009). The WCC biomass simulated using the parameters from Yeo et al (2014) was consistent with field observations conducted at different periods in this region . Therefore, we used the calibrated WCC biomass growth parameters provided by Yeo et al (2014).…”

“…The effectiveness of WCCs in reducing nitrate in this region has been investigated in several studies. The nitrate reduction efficiency has been shown to vary by implementation method, watershed characteristics, and crop rotation (Hively et al, 2009;Yeo et al, 2014;Lee et al, 2016). For instance, previous studies discovered that earlyplanted WCCs are more effective in reducing nitrate loads than late-planted WCCs due to warmer conditions and longer growing periods (Hively et al, 2009;Yeo et al, 2014;Lee et al, 2016).…”

“…Agricultural land covers only 25% of the CBW but has been reported to be responsible for 42% and 46% of total nitrogen (N) and phosphorus (P) loads, respectively, into the estuary (CBP, 2008). Nutrient loads have been shown to increase substantially during winter seasons in this region due to low evapotranspiration (ET), higher water table, and fallow cropland (Fisher et al, 2010;Yeo et al, 2014). Future climate conditions (FCCs; elevated CO 2 concentration, temperature and precipitation changes) are expected to affect the hydrology and N cycle in the CB, which potentially poses a threat to the health of the bay (Najjar et al, 2009(Najjar et al, , 2010Lee et al, 2015Lee et al, , 2017a.…”

“…The nitrate reduction efficiency has been shown to vary by implementation method, watershed characteristics, and crop rotation (Hively et al, 2009;Yeo et al, 2014;Lee et al, 2016). For instance, previous studies discovered that earlyplanted WCCs are more effective in reducing nitrate loads than late-planted WCCs due to warmer conditions and longer growing periods (Hively et al, 2009;Yeo et al, 2014;Lee et al, 2016). In addition, rye cover crops were found to outperform barley and wheat cover crops in reduction of nitrate loads, most likely due to their hardiness and more rapid root system development during the winter (Hively et al, 2009;Staver et al, 1989;Prabhakara et al, 2015).…”