Can Cover Crops Plus Cattle Be a Recipe for Improved Soil Health?


By Mary Drewnoski, Ph.D., Beef Systems Specialist, University of Nebraska

Source: Nebraska Cattleman Magazine

Many of the species promoted and utilized as cover crops can be excellent forage crops. One of the main goals of planting cover crops is improving soil health. Using the cover crops as a forage source can be a way to offset the economic costs of planting these cover crops. Naturally, this leads to the question: Can you have your cake and eat it too? Can cover crops be used for forage and still improve soil health? The simple answer is YES! You can use cover crops for forage while still reducing erosion potential and making other soil improvements such as improving soil microbial biomass and soil organic matter.

Fields that are harvested for wheat or corn silage can be excellent candidates for planting summer/fall cover crops and can produce abundant forage due to the greater number of growing degree days. Planting winter-hardy cover crops, such as rye, in late summer or early autumn can also provide forage in the spring. Late planting cold sensitive cover crops, such as oats and brassicas, following fall-harvested crops like soybeans typically does not provide enough time to accumulate sufficient biomass to support grazing animals prior to the onset of winter, so it is best to plant winter-hardy species, such as cereal rye or triticale, that can be grazed or harvested in the spring prior to planting of a summer crop.

Many producers are concerned that cattle trampling will adversely affect soil physical properties and subsequent crop productivity. Soil compaction, measured as an increase in bulk density or penetration resistance, influences the ability of a plant to acquire water, nutrients and oxygen and, consequently, can reduce crop yield. Grazing in late fall, winter or early spring can result in detectable compaction; however, the effects are usually confined to the 0- to 2-inch soil depth and small in magnitude.

Additionally, these effects are short lived due to natural processes of wetting/drying, freezing/thawing cycles, and root and soil organism’s actions. Therefore, such grazing typically has no impact on subsequent crop yields. Compaction due to grazing can be worse with low soil organic matter content, wet soil conditions during grazing or aggressive tillage. In the few studies that have shown reductions in crop yield, cattle were grazing when the soil was wet and, in most of these cases, the increased soil roughness resulted in poor seed placement of the cash crop.

It has also been shown that grazing during wet conditions can cause reduced water infiltration rates, offsetting the increased water infiltration gained by using cover crops. When cattle remained on the field during wet conditions, the grazed cover crop was equal in infiltration to the no cover control, while the cover crop with no grazing had increased infiltration. Thus, when possible, removing cattle during wet periods can help retain more of the soil health benefits of the cover crop.

Soil microbes perform many important functions in soils, including nutrient mineralization (making nutrients plant available) and formation of soil organic matter. After three years of winter grazing on no-till cropland, soil microbial biomass was 8 percent more when compared to the non-grazed cropland. Grazed systems are probably able to support more microbial biomass than non-grazed systems because the manure additions in grazed systems provide more easily decomposable organic matter than the plant material supplied in non-grazed systems.

However, increased soil microbial activity can have a downside. It can cause increased deterioration of residues on the soil surface. This is a positive from a nutrient availability standpoint but a negative in that if there is too little residue, increased water loss will occur due to evaporation. We have seen that in water-limited systems, the combination of grazing and increased microbial activity can result in greater risk for drought stress. The key in these systems is to ensure that more residue is left after grazing. Selection of the right cover crops with greater carbon-to-nitrogen ratios can also help.

Much of the soil organic matter benefits of cover crops are derived from the retention of root carbon. For instance, it has been found that root-derived carbon inputs are much greater (2.3 times as much) than top-growth contributions for oats. Based on long-term measurements of soil carbon captured from roots, shoots, and manure, grazing would not greatly impact the soil organic matter benefits of cover crops. The key here is that there is enough biomass remaining on the soil surface to prevent erosion, as loss of topsoil is a major loss of soil organic matter.

The bottom line is that grazing of cover crops can be an economical source of forage while retaining the benefits of cover crops such as erosion control and increased soil organic matter. Limited research results show that grazing is generally not detrimental to soil properties. Therefore, there are potential opportunities for both economic and soil benefits for producers to incorporate cover-crop grazing into their system.

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