Considerations When Applying Spring Nitrogen into Standing Cover Crops

When corn follows winter cover crops, remaining residue should be short-lived and low in Carbon:Nitrogen ratio, so as to not immobilize nutrients needed for raising the cash crop.

Applying spring anhydrous into standing grass cover crops (rye or annual ryegrass) may encourage growth and cause difficulties in terminating the stands. Most grasses that have roots and/or crowns disrupted will not take in herbicide as well as those left alone prior to burndown applications.

Depending on the region and weather, it is common for corn planting to follow a few days behind N applications. If this timing coincides with burndown, it could cause headaches. Now that NH3 tanks are rolling across the country, it is probably a safe bet that there may be an inadequate interval before planting to effectively control grass cover crops before planting corn. Spring management with cover crops isn’t necessarily difficult, if the appropriate plans are recognized ahead of time and followed.

In summary, we’ve found that when applying pre-plant N in fields where cover crops are still alive and growing, one should allow at least a week to ten days before burndown to permit proper herbicide translocation (especially when using glyphosate). To eliminate the possibility of inadequate weed control (and lessen some of the risks associated with planting green), terminate the cover crop stand prior to pre-plant nitrogen applications.

What Happens when Cover Crops Overwinter that Should Not?

Depending on the severity of the winter, some cover crops that normally winterkill may survive. One should keep in mind that USDA Hardiness Zones  were established to better predict survivability of plants, given their respective winter hardiness. These zones stay true for the most part, however factors like snow cover, soil moisture and plant population all impact a plant’s ability to persist up to or beyond their projected growing zone. Click here to see USDA Hardiness Zone numbers for Soil First products.

In addition, increased accumulation of sugars (or carbohydrates) through photosynthesis helps plants survive tough conditions too. As sugars build in plants, the percentage of water decreases. Increased sugar, along with less water in cell tissue, help serve as a natural antifreeze for plants, which aids in their ability to tolerate colder air and soil temperatures.

Augmenting Stands of Cover Crops Used for Spring Forage

For those counting on covers for forage production, there are options to augment the stand. We have heard several reports of thin stands of wheat and other small grains this spring. If you plan to harvest the stand for forage, you may consider adding another species (or two) to boost production and keep out winter annual weeds. The way we address this is by leaning on basics that have the highest probability of success, assuming you have at least 70-90 days before an expected harvest (which coincides with normal small grain balage or silage practices):

• Spring Oats. Planting window lasts through early April for much of the Northern U.S. An added shot of N will be needed, but production could be as much as a ton or more in 70-80 days. If the plan includes grazing, wait until oats are at least 8-12” tall. If making hay, plan to harvest at boot-early heading stage to optimize both tonnage and quality; however, the existing small grain will probably be the barometer.
• Red Clover. Spring seeded red clover can also be cut around 70-80 days after seeding if soil temps and weather allow. Aggressive cutting in the planting season (with a later cutting around September in the Corn Belt) often results in better stands the year after seeding. Once red clover is established, we recommend harvesting at pre-bloom or early-bloom. Red clover by itself can be difficult to cure for hay, but harvesting mixed stands containing grasses usually results in decreased curing time.
• Cool-Season Grasses (annual ryegrass and/or timothy). Annual ryegrass can thicken stands while boosting quality. If soil temps can hold above 40⁰ F, then annual ryegrass and timothy can germinate very well, assuming seed-to-soil contact is optimized. The advantage of ryegrass is quicker establishment, whereas timothy has long been a viable option for over-seeding due to its small seed size, which enables it to compensate for less than ideal seedbed conditions.