With the explosion of interest in cover crops for soil health benefits, many questions are being asked where no real information exists to substantiate the possible answers. The anticipated changes in soil health resulting from cover crop management can take several years or decades to happen. There are many questions about using cover crops as a grazed or mechanically harvested forage since this is the quickest way to recover some production costs associated with establishment.
The overall goals and primary objective for growing and managing a cover crop make it entirely different from a forage crop. The first questions to ask are:
1. Will it be managed only as a cover crop to reduce soil erosion, reduce soil compaction, increase organic matter, or reduce nutrient leaching?
2. Will it be managed primarily as a cover crop with forage production as a secondary outcome if enough production is available?
3. Can it be managed as a forage crop first with potential for simultaneous cover crop benefits?
There is not much information on seasonal production and forage potential for many of the annual grasses and broadleaf species used as cover crops. Regardless of planting date, growth will slow by October 1 and cease with the first killing frost. The non-winter hardy species and varieties have minimal or no cold tolerance and will not resume spring growth. The winter hardy species and cultivars require a combination of cold temperatures and high humidity coupled with short days to trigger the elongation and flowering process. These will usually resume growth in the spring sometime in March.
A common question is “when can grazing begin without harming cover crop function?” There are few definitive studies that give guidelines, much less a successful recipe for managing cover crops as forage crops. There are two studies on small grain forage production that can provide some initial guidance and direction to address this question. A study conducted in Canada found that root mass production under light, moderate, and heavy grazing intensity was not different for triticale. Root mass production was almost 3500 pounds per acre in the top 12 inches of the soil profile with about 60% in the top 6 inches and 40% at the 6- to 12-inch depth. An Australian experiment found that grazing had no substantial effect on rooting depth or root mass in wheat unless it was grazed during early growth when the primary root system was still developing. Based on these results, properly managed grazing appears to have little impact on root growth of small grains managed as a grazed forage crop.
In the western Corn Belt, numerous opportunities exist for providing additional forage that has been planted following harvest of hybrid seed corn, small grains, and corn silage. For many of the species planted to provide soil cover at a minimum, light to moderate grazing can begin in early October without reducing the soil health benefits of the cover crop. Management of annual forages, especially the small grains and brassicas, should focus almost solely on biomass production. To increase the probability of success, it is important to plant as soon as possible following harvest of the primary crop.
1. Make sure that adequate cover remains regardless of forage defoliation method. The primary purpose of a cover crop is to provide cover; grazing should be a bonus.
2. For late-summer planted forages and cover crops, fall grazing can begin around October 1st. A minimal amount of additional growth will occur after early- to mid-October. The growth of the above-ground and below ground biomass should be 90% completed.
3. Leave at least 4 inches of residue after grazing or mechanical harvest. This is important for:
a. Soil conservation, especially following corn silage or grain crops grown on sandy soils or those with increased susceptibility for erosion.
b. Snow capture to increase soil moisture for the following crop.
4. For many winter annuals, such as the annual, small grains currently used as cover crops and forages, the best trade-off is to manage them to meet forage production goals, such as forage yield and quality.