By Sjoerd Duiker, Soil Scientist
Last year, we started a USDA-SARE funded project on planting green. At four locations (two at research stations, two at working farms) corn was planted green after crimson clover, rye or a mix of both, and compared with corn planted after these cover crops that had been killed about 2 weeks earlier. The corn yields were lower in the planted green plots at two locations. Corn population was significantly lower in planted green plots at one of those.
Soybeans planted green after rye had the same yields as soybeans planted after early killed rye.
Last year we had a dry spring and we attribute much of the reduced yield in the planted green corn to that. Farmers on our advisory board told us they would have “pulled the trigger” on the covers when they saw no rain in the forecast.
So how does this spring look? As you can read in the Pennsylvania Climatologist report, rain is in the forecast over the coming week, with cool temperatures, so it does not seem warranted to terminate cover crops as yet if you were planning on planting green. Keep a tab on actual vs. predicted rain, however.
Based on maturity of the cover crop, you should probably also adjust your nitrogen (N) program. If the cover crop is killed early, carbon-to-N (C:N) ratio will be low. In the Cover Crop Chapter of the Penn State Agronomy Guide, you’ll find information about the C:N ratio of rye and how it changes during the fall to spring. In early spring, its C:N ratio will be 20, progressing to 30 by mid-spring, and finishing at about 40 at the end of the spring. If you plant green into 6 feet tall rye, you should plan on adding extra N so your corn doesn’t run out of it.
At the moment we don’t have guidelines how much you have to add, but it is probably wise to add another 30 pounds per acre or so. It would be best to place this as close to the corn seed as possible without causing seed burn or salt injury. The rule is no more than 70 pounds per acre of N and potash within 2 inches of the seed, and no more than 10 pounds per acre of N and potash in pop-up starter. If you apply N fertilizer or manure on a cereal or grass cover crop in the spring, it is probably not necessary to apply extra N even if you plant green. No extra N should be needed if your cover crop is a legume or balanced legume/grass mix.