Jarrod O. Miller, Extension Agronomist, jarrod@udel.edu , Jamie Taraila, Graduate Research Assistant, and Amy Shober, Extension Nutrient Management and Environmental Quality Specialist; ashober@udel.edu
Farmers must make several decisions when considering termination of cover crops. Early termination is typically the easiest option, since it reduces issues related to planting into a standing cover crop. In 2018, planting green decreased corn stands by 10,000 plants per acre in our Sussex County research plots. This type of stand reduction when planting green is not expected for all soil or cover crop combinations. Certainly, having good soil moisture and some luck can help to increase plant populations when planting green, but the biggest factor affecting stand establishment is seed placement and depth. As such, it is important to get out and check seed placement and depth when planting green, making any adjustments to the planter as necessary. For example, we found that simply raising our row cleaners provided us with better planting conditions when planting green into our research plots in Georgetown.
With support from USDA-NRCS, we are evaluating the effects of four cover crop single species or mixes (none, rye, rye/vetch, and rye/clover) and two termination timings on commodity crop performance (corn, soybean rotation). We currently have one year of data from this study, which was conducted at two sites in 1) Georgetown (sandy, irrigated soils) and 2) Middletown (finer-textured, non-irrigated soils). When planting corn behind cover crops, we noted no corn yield effects due cover crop species at Georgetown. However, waiting to terminate the cover crop until closer to planting resulted in a yield penalty of about 16 bu/ac. Results were quite different at Middletown, where corn yields were 12 to 15 bushels greater when corn was planted into plots with cover crops than in plots with no cover crop. Our results also suggested that soybean yields at both sites were increased when planted behind a cover crop (compared with soybean planted into plots with no cover crop). Soybean also appears to be more tolerant of late cover crop termination, as it had no effect on yield when compared to no cover crop or early termination. Therefore, farmers have more options of when to terminate cover crops before planting full-season soybean. It is important to note that our observations for the 2019 are preliminary. We will repeat this study for the next two seasons, which will help us determine if these results were significant. Yet, we assert that managing cover crops can be complex as their impact on crop yields can vary annually, by soil type, and by cropping system.