Corn silage is commonly fed to dairy cattle and other types of ruminant livestock, but its production can leave cropland vulnerable to nitrate leaching and runoff of nutrients and sediment. As result, a wide variety of cover crops or living mulches (collectively referred to here as “companion crops”) have been developed and promoted to mitigate the adverse environmental impacts of corn production and to improve crop yields, nutrient cycling, and soil quality. Based on a review of the literature, a few of the more promising companion crops for corn in north-central states such as Wisconsin include winter rye, Italian ryegrass, red clover, alfalfa, and kura clover.
Winter rye is commonly seeded in the fall after corn harvest. Although it often provides little ground cover in the fall and winter, fall-seeded rye grows vigorously during the spring to protect soil and remove residual soil nitrate. Rye can be grazed or harvested for forage prior to a late planting of corn, but earlier spring termination is often used because more mature rye can in some cases deplete soil moisture, immobilize nitrogen, and depress corn yields.
Italian ryegrass is usually interseeded in June about 4 to 6 weeks after corn planting to permit establishment without excessive competition with corn. In the fall, interseeded ryegrass usually provides greater ground cover and soil nitrate scavenging than fall-seeded rye and it can be grazed or harvested for forage. Ryegrass often winterkills to provide short-lived mulch for spring-seeded crops such as corn and it tends to have a neutral effect on corn yields unless its growth and uptake of soil nitrate are too vigorous.
Red clover or alfalfa are also typically interseeded in June to prevent excessive competition with corn, but such seedings are prone to fail during dry summer conditions or if corn growth is especially vigorous. If successfully established, interseeded red clover or alfalfa will normally overwinter to provide moderate ground cover and uptake of soil nitrate during both the fall and spring. Red clover and alfalfa cover crops supply nitrogen and often boost yields of subsequent corn crops. A seemingly overlooked option would be to keep interseeded red clover or alfalfa in production for at least one year after corn to provide high quality forage and to further boost subsequent corn yields through greater nitrogen and non-nitrogen rotational effects. This system would be most workable if forage legumes could be interseeded immediately after corn planting, but new approaches are needed to lessen yield-killing competition between the co-planted crops.
Kura clover may also serve as a dual-purpose crop that can be used one year as a living mulch for corn and then kept in production in following years as a forage crop. Corn grown in kura clover can produce yields comparable to corn grown after killed kura clover, but excessive competition from the living mulch can depress corn yields. Following corn production, kura clover living mulch can recover to full forage production by midsummer of the following year. The performance of the kura-corn system has not, however, been directly compared to other companion crop systems for corn.