Cover Crops: Good & Bad

Farmers seem to either lover or hate cover crops. Cover crops have many benefits, but they may be hard to see immediately. First the bad or difficult things about cover crops will be discussed followed by the benefits.

Cover crops cost money for seed, planting, and sometimes termination. It takes more knowledge and experience to plant cover crops and to use it with no-till (school of hard knocks), so its risky at first. The timeliness factor, getting cover crops planted on time and established is difficult. Herbicide carryover can be an issue and sometimes it requires different equipment (no-till, sprayers, spreaders) although less or no tillage equipment if used in a no-till system.

Then there are the pests (slugs, voles, cutworms) that love a good feast. Cover crop residue may have an allelopathic or negative growing effect on the grain crop. It can be difficult to plant timely if soils stay cold and wet (sounds like a compaction problem) and sometimes planting is delayed and soil get hard and dry. Then crop yields can suffer greatly especially if mistakes are made. That sums up most of the bad.

Here is the good. Soil erosion is greatly decreased when no-till (1/3 of solution) and cover crops (2/3 of solution) are used together. Average USA soil erosion rates are 7.6 tons/acre or about 5 pound of topsoil lost for every pound of soybean produced (assumes 50 bushel soybeans). In Ohio, that about 2.5 tons or roughly 1.33 pounds soil lost per pound of soybean produced.

Fertilizer use decreases and nutrient use efficiency increases. Every live root is a host to 1000- 2000X more microbes, each is a soluble bag of fertilizer. Each root and microbe increases soil organic matter (SOM) which is a storehouse for soil nutrients. Microbes process 90% of the soil energy and soil nutrients. As more cover crops are used continuously, farm inputs for pesticides (herbicides, fungicides, insecticides) should go down as the farm becomes more sustainable. Less fuel, labor, and equipment are needed.

No-till and cover crops lead to higher soil carbon and higher SOM. This improves soil structure and reduces soil compaction over time (may take 3-7 years). Aggregate stability improves so now water infiltrates the soil rather than running off taking nutrients with it. Increasing SOM by 1% leads to greater water storage (sand 0.5 acre inch, silt loam 0.8, clay 0.6). This improves a soils ability to resist drought conditions. Cover crops improve drainage, and the soil is cooler in the summer and warmer in the winter, improving plant water usage.

Often the transition period (3-7 years) is what makes adapting no-till and cover crops difficult. Poor soil structure and soil compaction is the real culprit. Saturated soils in early spring are cold and wet. It takes 10X more energy to warm up water than air. Tillage dries out the soil (0.5-1.0 acre inch of water) per tillage pass. However, it also burns up carbon and reduces beneficial soil aggregates. As cover crop roots improve water drainage, soils get warmer. Increased SOM turns the soil black, warming spring soils that were cold. The increased microbial activity in a soil generates heat (think compost pile), so over time, soils become warm and moist, not cold and wet.

The H2O Ohio program pushes cover crops for the water quality and environmental benefits. A good cover crops stand may reduce soil erosion by 90% and reduce nutrient and pesticide runoff by 50% or more. Research shows stream sediment loading reductions of 75% and reduced pathogen loading of 60%. Cover crops may even have the potential to decrease flooding by increasing water infiltration, storing water longer in the soil, thus reducing how quickly water leaves a field or flash flooding.

Other benefits from cover crops seldom discussed is the forage and grazing value. Cover crops like sorghum, oats, clovers (Balansa, crimson, red, sweet) winter peas, hairy vetch, turnips can all be fed to livestock. From a nutrient density standpoint, the soil becomes more healthy; creating healthy plants, and healthy animals and people who consume those plants. Today a person has to each 2X as much meat, 3X as much fruit, and 3-4X as many vegetables to get the same amount of micro-nutrients as a person eating food in 1940’s. That a huge decline in nutrient density that healthy soils and healthy plants can help recover.

Due to drought resiliency, better water and nutrient management, and healthier soils; crops yields do increase over time. A Michigan State University study reported a 12% increase in crop yields or every 1% addition in SOM. Cover crops have many benefits but it takes time to see them accrue.