By Daren Redfearn, Extension Forage Crop Residue Specialist
Several areas of the state have had significant weather-related damage to corn and soybean fields. Not only has grain production been reduced or eliminated, much of the residue usually available for winter forage has been lost.
This is an opportunity for those who may not yet have tried a cover crop to do so, particularly if they are interested in producing a high-yielding, high-quality forage crop that will offset some, if not all, of the lost fall and winter grazing potential from corn residue.
Selecting Annual Forage Cover Crops
With annual forage cover crops, there is a short window for forage growth. Mixes can include many species, each of which should have a defined contribution. If the goal is forage production, either for grazing or hay, the mixes need to be predominately grass. Generally, no less than 75% of the mixture should be a grass (the higher the better) for summer planting.
Occasionally, mixes will have a lower proportion of grass in an attempt to promote growth in other species. If forage is the stated goal, this can be a mistake. This does not mean that other species cannot be added, but it is important that the proportion of grasses in the mix not be reduced.
There are many opinions on the use of diverse cover crop mixes (more than 10 species), but not much data to support their widespread use. What we have seen in diverse mixtures is that legumes do not provide the yield for the seed cost. From a forage production standpoint, the grasses are the biomass producers. For the legumes to provide additional nitrogen (N), soil N should be low; otherwise, legumes will use soil N and not fix their own. Actually, legumes are excellent at removing excess soil N.
This table from Beef.unl.edu outlines planting guidelines for individual annual forage species, including planting dates, seeding rates, seeding depth, and grazing value. For mixtures, target the percent of the full seeding rate of the species to add up to 100% to 150%.
For example, if cereal rye and hairy vetch are planted in a mixture, a seeding rate of 50 lbs of rye (50/65 = 77%) and 9 lbs of vetch (9/20 = 45%) would be 122%. (The full seeding rate for each would be, respectively, 65 lb/ac and 20 lb/ac.) Again, it is important to not reduce the proportion of grass in the mixture. For July planting use the table section, Late Spring Planting (July-September Grazing) and look for warm-season species.
Logical Forage Options
One option is a sorghum x sudangrass for haying, stockpiling, and windrow grazing during winter. It will have the greatest yield for a one-time harvest. Sorghum x sudangrass does not grow well after grazing. This is evident when it's grazed so that much of the stem is removed. When grazing does not begin until the plants are mature and animals do not graze enough of the stem, regrowth often mainly consists of spindly leaves.
For grazing only, sudangrass is a better option; however, it is better managed and will regrow better if grazed 45 days or so after planting, allowed to regrow, and then grazed again. Given the timing of planting in mid-July, this is a bit of a push because after the first grazing it’s apt to be late enough in the season that temperatures will be cooler and regrowth will be slower. In some years this may work well, but in other years, it may not.
It may be best to select a forage based on when the grazing is needed:
- If summer grazing is a possibility, sudangrass would be the first option.
- If grazing will be in the fall, sorghum x sudangrass might be a better option. That said, pearl millet also could be used. It will produce less forage than sudangrass or sorghum x sudangrass, but it can be grazed during frost with reduced risk from prussic acid poisoning.
- If grazing is needed in late September and other grazing options do not exist, pearl millet would be a better choice than the sorghum species.
Forage sorghum is not a good option, except for silage.
Information, especially the grazing management recommendations, in Summer Annual Forage Grasses (NebGuide G2183) may be useful.
The two primary agronomic issues to consider when planting forage cover crops after hail-damaged corn or soybean are planting date and high residual soil N, along with possible nitrate issues.
Warm-season species should be planted before August 1. After August 1, cool-season species such as oats and rapeseed will be a better option. After October 1, cool-season winter annuals are best. For more information on cool-season cover crops see NebGuide G2262, Annual Cool-Season Forages for Late-Fall or Early-Spring Double-Crop.
For more information on possible nitrate issues, see Reducing Nitrate Concerns When Grazing Forage Cover Crops, which includes management strategies to mitigate nitrate toxicity.