Potential for a rye cover crop to reduce nitrate loss in southwestern Minnesota

Cover cropping practices are being researched to reduce artificial subsurface drainage NO₃-N losses from agricultural lands in the Upper Mississippi watershed. This study was designed to investigate the influences of fall planting date and climate on cereal rye (Secale cereale L.) biomass and N uptake in the spring, and to assess subsurface drainage NO₃-N loss reductions. A soil-plant-atmosphere simulation model. RyeGro, was developed and used to predict rye cover crop establishment and growth, soil water balance, N cycling, and drainage NO₃-N losses from mid-September through May in southwestern Minnesota. An imbedded stochastic weather generator provided model climate inputs. Inclusion of a rye cover crop sown on 15 September reduced N losses by 11.1 kg N ha^-1 or 45% for a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] crop rotation. Fall sowing dates of 1, 15, and 30 October resulted in reductions of 7.8, 5.8, and 4.6 kg N ha^-1, respectively, by the end of May. Desiccation of the rye on 1 May resulted in reductions of 45, 2.2, 1.2, and 0.7 kg N ha^-1, for the 15 September and 1, 15, and 30 October sowing dates, respectively. Cover cropping practice provides promising opportunities for reductions in N losses for cropping rotations wherein the primary crops are harvested before mid-September and planted after mid-May. We predict that a winter rye crop can reduce drainage NO₃-N losses on average 7.4 kg N ha^-1 for southwestern Minnesota if planted on 15 September and desiccated on 15 May.