Modeling the impact of winter cover crop on tile drainage and nitrate loss using DSSAT model

Increasing demand for food has amplified the use of fertilizer. Intensive agriculture practices in the Upper Mississippi basin have been linked to the formation of a hypoxic zone in the Gulf of Mexico. Previous studies have recommended the use of winter cover crop in the maize-soybean rotation as an eco-efficient solution in reducing the nitrate-nitrogen (NO₃-N) loss via a sub-surface drainage system. Therefore, the objective of this study is to evaluate the impact of cereal rye as a winter cover crop in the maize-soybean system on reducing nutrient loss via tile drainage using the DSSAT model. The experiments include four treatments with a combination of two different nitrogen (N) application timing with cover crop (CC) and without cover crop (NCC): fall-applied N without cover crop (FN), spring-applied N without cover crop (SN), fall-applied N with cover crop (FCC), and spring-applied N with cover crop (SCC). The calibrated DSSAT model was utilized to assess the impact of the cover crop by comparing NO₃-N losses and cash crop yields between CC and NCC treatments for different N fertilization timings. The model calibrated for cereal rye biomass in the FCC treatment estimated the observed cereal rye growth for SCC treatment considerably well (R² >0.91). The model successfully predicted the impact of cereal rye on nitrate loss and tile drainage with 43.6% and 45.4% (48.6% and 47.8% observed) nitrate loss reduction and 21.3% and 21.0% (30.2% and 19.4% observed) tile drainage volume reduction in fall and spring N application treatments, respectively. The results from this research suggest that DSSAT can predict the cereal rye growth and assess the soil water-nutrient dynamics in both CC and NCC systems. However, the model was not able to replicate the impact of cereal rye on the cash crop yields due to the higher N mineralization simulated in the CC compared to the NCC treatments. This could be due to the use of glyphosate to terminate the cereal rye and the presence of tillage radish along with the cereal rye. The glyphosate application hastens the decomposition process; however, it also reduces the overall residue. The chemical termination and intercropping feature are not available in the DSSAT model currently. The cereal rye hosted pathogens and pests might also be responsible for lowering maize yield in the observations.