For many parts of Iowa, 2023 is the third consecutive year of drought conditions. This has made establishing cover crops challenging. Drought conditions make overseeding cover crops into standing corn and soybean less successful because of a lack of rainfall to get seeds to germinate. Advice to this point in the growing season has been to postpone overseeding of cover crops (or if you were lucky, overseed ahead of the past weekend’s rain).
Instead of overseeding, the best chance of getting adequate cover crop establishment this fall is to drill seed following soybean or corn harvest. This will provide the best seed to soil contact and therefore best chance of the seed absorbing moisture to initiate germination. In the driest areas that missed last weekend’s rain, it will still take some rain. However, drill seeding will protect more of the seed from scavenging birds and rodents.
A second best practice for planting cover crops in a drought year is to switch to winter small grains like cereal rye, winter wheat, or winter triticale. These species are fast to germinate and can tolerate cooler temperatures than brassica and legume species. Additionally, in the spring they will get off to an early start and have the potential to produce large amounts of biomass.
Oats would be another alternative if you are able to drill seed before October 1. In most cases, this will be fields that have been harvested for silage corn, high moisture corn, or early maturing soybean. The oats will winter kill. To get the most out of oats consider seeding at greater than 60 pounds/acre.
Regardless of the timing of cover crop seeding, consider doing a bioassay to determine if there are residual herbicides that would impact the germination and growth of a cover crop this fall.
Cover crops are a great non-herbicide tool for suppression of problematic weeds. One attribute of cover crops that help control weeds is having the ability to produce large amount of biomass. If weed suppression is your cover crop goal, make sure to seed at a higher seeding rate (greater than 70 pounds/acre for most small grains).
Keep an eye on the U.S. Drought Monitor and how much rainfall and snowfall you have received. Factor in how much water is infiltrating (aka soil moisture recharge) versus running off from high intensity storms or as snow melt on frozen soils. If soil moisture reserves have not been filled and precipitation patterns indicate a dry spring, consider terminating overwintering cover crops early to avoid early and shallow soil moisture deficits for the 2024 corn and soybean crop.