Many cover crop species are excellent at accumulating nitrogen and making it available for the following cash crop. Is it advantageous to apply supplemental N to cover crops?
One goal of farmers using cover crops is to reduce nutrient loss and possibly reduce commercial nutrient inputs. Is there value in spending additional money to apply commercial fertilizer to cover crops in these times of narrow profit margins?
In many cases, farmers are using cereal rye either flown into standing corn or seeded immediately after corn is harvested, especially if soybeans are the next planned cash crop. If the corn has yields near the planned levels, much of the available nitrogen has been removed from the soil. Although cereal grain needs N to thrive, there is still likely enough N left and more that will become available when the residues start to break down. Yet the decision depends on your goals and other factors.
If water quality is a concern, then don’t apply additional nitrogen. If water quality isn’t the major concern and you’re trying to improve your soil organic matter levels with high-carbon cover crops, it’s important that they get off to a good start in the spring, coming out of dormancy. An application of 20 to 30 pounds of N per acre may improve early spring growth, lead to more biomass and improve soil organic matter levels.
If manure is available, it’s a smart move to put manure where you will have or already have cover crops. Cover crops can hold as much as 90% of the nutrients from manure applications. These nutrients will be stored and made available for future cash crops. Never apply manure to ground that is frozen, snow- or ice-covered, or saturated — even if a cover crop is in the field.
Another option is to include a legume such as crimson clover in your cover crop mix, even if you will not be planting corn. The legume will produce easily available N that the grass cover crop can use, as well as providing diversity in the cover crop mix for microbiology in the soil.
Should manure not be available or you don’t wish to include a legume in your cover crop mix, you can easily get some nitrogen by applying your next year’s crop needs for phosphorus in the fall near cereal rye seeding time. Both MAP (11-52-0) and DAP (18-46-0) include N with P. Only apply supplemental N after the cover crop has emerged to avoid excess fertility if conditions such as a late planting date or dry weather keep the cover crop from properly emerging in the fall. Never apply fertilizer to ground that is frozen, snow- or ice-covered, or saturated, either.
It’s always important to remember that you need to treat your cover crops like you treat your cash crops. Things such as seed selection, proper planting methods, timely planting and proper fertilization are critical for establishment and success of cover crops! That’s why you may want to consider supplemental fertilizer application as part of your cover crop management plan.
Donovan is a district conservationist with the Natural Resources Conservation Service. He writes on behalf of the Indiana Conservation Partnership.