By James Hoorman, Hoorman Soil Health Services
Fall harvest has started but farmers also need to think about planting cover crops. USDA-SARE publication (10 Ways Cover Crops Enhance Soil Health) states “Cover crops lead to better soil health and potentially better farm profits.” Here is a 10-point summary.
Cover crops feed many soil organisms. Most soil fungi and bacteria are beneficial to crops, feeding on carbohydrates that plants exude (release) through their roots. In return, fungi and bacteria supply nutrients, such as nitrogen or phosphorous, to the crop roots. While cover crops directly feed bacteria and fungi, many other soil organisms eat fungi and bacteria, including earthworms and beneficial arthropods (soil insects). Cover crops support the soil food web throughout the year. Beneficial soil insects eat weed seed, devore crop predator eggs and larva, and consume or outcompete many crop disease organisms. Good soil health means that all soil organisms are kept in balance so no one organism becomes a pest.
Cover crops increase the number and type of earthworms. Some earthworms, like nightcrawlers, tunnel vertically, while the smaller redworms tunnel horizontally. Both create growth channels (stable pores) for crop roots and for rainfall and air to move into the soil. Cover crops also build soil carbon and soil organic matter, using sunlight and carbon dioxide to make carbon-based molecules to buildup soil carbon. Some carbon is a direct food source (sugars) while some becomes humic (stable) substances that build soil organic matter to improve nutrient availability/storage and hold soil moisture.
Cover crops improve soil nutrient management, reducing the need for some commercial fertilizer. Cover crops scavenge and recycle soil nutrients to the next crop (nitrogen and phosphorus) keeping them in the soil, not losing them to the air or water. Bare soils tend to crust, have reduced water infiltration, and erode. Cover crops cover the soil, keeping soil moist and cool, for optimal plant and microbial growth.
Cover crops greatly reduce soil erosion loss, especially on sloped fields where half the topsoil has already been lost. The future success of farming and our food supply depends on keeping topsoil in place and cover crops are exceptional at stopping erosion. Using no-till with cover crops reduces soil erosion to a tiny fraction compared to a conventional corn and soybean system. Even with light tillage, cover crops protect the topsoil, especially with winter annual cover crops like cereal rye.
Cover crops improve plant biodiversity by growing live roots which promotes higher numbers and types of soil organisms, leading to healthier soil. Growing cover crops such as cereal rye before soybeans, and oats, radishes or crimson or Balansa clover before corn—improves diversity. Many farmers add wheat and then grow diverse cover crop mixes. For livestock, these cover crop mixes can be grazed or used for forage, and the animal manure benefits soil biology. Beef and dairy cattle, sheep, and horses can utilize the forage. In the past, buffalo herds foraged prairies, increasing soil organic matter leading to increased soil productivity. Livestock manure from cover crop forages builds organic matter and improves soil health. Cover crops create high-quality forage in late fall or early spring for immediate farm profit.
Cover crops aerate the soil and helps rain get into the soil (infiltration). Cover crop roots improve soil structure so that rain infiltrates instead of running off, improving crop yields in mid-to-late summer when it rains hard and then becomes dry. Tillage has been the typical solution to heavy farm equipment compaction, but only compounds the problem long term. Excess tillage destroys soil structure, while cover crops and soil organisms create glues (glomalin) that binds soil particles together, leading to better soil aggregation and strong soil structure. Research has shown that cover crops and earthworms can effectively loosen compacted soil better than subsoiling equipment, saving diesel fuel. A field with cover crops and minimal tillage, or better yet no-till, leads to improved soil structure with reduced soil compaction.
Soil health is a hot topic these days. An incredible diversity of bacteria, protozoa, arthropods, nematodes, fungi and earthworms create a hidden soil food web that affects how crops grow, how soil nutrients are cycled, and how precipitation and moisture are utilized. In soils with good soil health, soil nutrients and water are used efficiently, while degraded soils loose soil nutrients to water and nutrient runoff. In the past, soil testing and evaluation focused mostly on chemical and physical measures, but new research has shown that the soil biology is important to soil health and crop productivity.