Nitrogen use with integrating cereal rye grain production and clover cover crop into a soybean-corn system
Winter cereal rye (Secale cereale L.) has been a common cover crop choice due to seed cost, winter hardiness, rapid growth, and excellent potential to reduce NO3 losses to the environment. It could also be an alternative grain crop to include in a corn (Zea mays L.) – soybean [Glycine max (L.) Merr] rotation, although detailed information on management practices for cultivation in Iowa is lacking. In addition, insertion into the cropping system of a different cover crop, like the legume red clover (Trifolium pratense L.), would be possible due to inter-seeding with the cereal rye small grain crop. Such a cover crop would also provide an alternative source of N for a subsequent cereal crop such as corn and positively impact NO3 leaching due to extended growth after rye grain harvest. The objectives of this study were to determine N response and optimal fertilizer N application rate in cereal rye production, the impact of a red clover cover crop on rye growth and yield and on a subsequent corn crop optimal N fertilization requirement and yield, and the influence of the cropping system on soil profile NO3. Two cereal rye varieties were no-till planted following soybean harvest in the fall 2017 and 2018 at two locations each year, Ames and Kanawha, Iowa. Six total fertilizer N rates (0, 28, 56, 84, 112 and 140 kg N ha-1) were fall-spring split applied. The study was split with and without late winter inter-seeded medium red clover. Rye crop canopy sensing was collected multiple times during the growing season, and plant height, number of seed heads, leaf and grain N concentration, and grain yield were measured. In addition, soil profile NO3 was determined after rye harvest. The red clover was allowed to grow until termination the next spring prior to no-till corn planting. Six N rates (0, 56, 112, 168, 224 and 280 kg N ha-1) were planting-sidedress split applied to the corn. Corn canopy sensing was collected at mid-vegetative growth and ear leaf sensed at silking, and grain yield determined. Soil profile NO3 samples were collected multiple times during the season. The inter-seeded red clover had no effect on rye N response or yield. Both rye varieties responded to N rate with increased plant canopy sensing indexes, leaf greenness, head count, plant height and grain yield, but with growth and yield differences between varieties. The yield at the agronomic optimum N rate (AONR) was higher for ND Dylan at 3120 kg ha-1 versus 2119 kg ha-1 for Elbon. However, the mean (AONR) was similar for both rye varieties at 98 kg N ha-1. Overall, the rye yields were relatively low. Post-rye harvest soil profile NO3-N was low with all N rates. Corn canopy sensing was greater with the presence of clover when N application was deficient, showing evidence of N contribution from the terminated red clover. The clover supplied corn with an estimated mean 57 kg N ha-1; therefore reduced the optimal N rate needed to maximize grain yield. Soil profile NO3-N was minimally increased with the clover at termination and late spring, however, following corn harvest was elevated with the higher N rates indicating care is needed to account for N supplied from the red clover cover crop. Further research is needed to assess management practices that promote better rye performance. Even so, this integrated grain crop-cover crop production system has potential for an alternative rye crop within the traditional corn-soybean rotation, and to help reduce system-wide profile NO3 loss.