Impacts of nitrogen application timing and cover crop inclusion on subsurface drainage water quality

Significant reductions in nitrogen loading from sub-surface drainage fields of the Upper Mississippi River Basin to the Gulf of Mexico will most likely be achieved from the mass adoption of nutrient loss reduction strategies at a watershed scale. Few studies have quantified the efficacy of cover crops to reduce NO3-N loading in nitrogen fertilizer management systems, where the dominant portion of the N rate is applied in the spring or fall, both of which are common practices in the Upper Mississippi River Basin. In this experiment we quantified the impact of N application timing and cover crop inclusion on NO3-N loss (leaching) from agricultural sub-surface drainage within five nitrogen management scenarios: a zero control, applying the dominant portion of the N rate in the spring, applying the dominant portion of the N rate in the fall, augmenting the a spring and Fall N application system with cover crop. Each of the five nitrogen management scenarios was replicated three times on individually monitored sub-surface drainage plots established in Lexington, IL. During the experiment, a cereal rye (Secale cereal L.) and radish (Raphanus sativus L.) blend was interseeded within both corn (Zea mays L.) and soybean (Glycine max L.). Fertilizer N application timing did not affect cover crop growth or N uptake. The inclusion of cover crop resulted in more consistent and greater NO3-N loss reductions relative to adjusting fertilizer N application timing from fall to spring. Cover crop reduced the flow-weighted NO3-N concentrations by 39% and 38% and the N load by 40% and 47% when added to spring and fall fertilizer N management systems, respectively. Cover crop proved to be effective in reducing NO3-N loss through sub-surface drainage across the spectrum of N fertilizer management systems common to the Upper Mississippi River Basin.