Our friend Rob Myers from the University of Missouri has likened cover crops to the “Swiss Army knife” of the Soil Health world because of the incredible diversity of functional benefits that cover crops bring to the table. Here are a few of the ecosystem functions of cover crops.
Reduced Soil Erosion
Reduced soil erosion was the original usage of cover crops, and they still work as well as ever for keeping your soil in your field! This works even better when combined with no-till farming rather than being plowed down as they were in the past.
Improved Infiltration Of Rainwater And Reduction Of Runoff And Flooding
While cover crops use moisture to grow, much of this use is offset by enhanced infiltration of rainfall. In one Kansas study, a field of wheat stubble planted to a sunn hemp cover crop had triple the rate of infiltration as the no-till wheat stubble next to it. This is not only a benefit to the landowner but the reduced downstream damage from flooding and sedimentation in times of heavy rain is incredibly valuable for both the environment and society.
Improved Water Quality
Less water runoff also means less soil, fertilizer and chemicals runoff. This not only saves money for the farmer but reduces the problem these things create in drinking water. Cover crops can also take up unused nitrate from fields during the winter, keeping it out of wells and drinking water. Many wells in Nebraska and Kansas have nitrate levels in their water that exceed what is safe to drink, and to treat this at the municipal level is extremely costly.
The mulch residue left behind by a cover crop reduces the evaporation of soil moisture, increasing the time a crop can grow until it begins to wilt after each rain. One Kansas study found that a field covered in residue had three inches less evaporation during the growing season than a field with no residue.
Improved Soil Trafficability
Cover crop residue and root mass help increase the weight bearing ability of soil, which allows traffic and field operations at much higher levels of soil moisture than could be possible with tilled or bare soil. Also, the higher level of soil organic matter created by long term cover cropping reduces the problems of planting in wet soil, like the seed trench remaining open, sidewall smearing, and soil compaction from tires.
Increased Soil Organic Matter
Cover crop roots produce root exudates that feed soil microbes that produce soil organic matter. While a single cover crop may not have a major impact on soil organic matter levels, cover cropping as a routine part of the system will have compounding benefits. We have many customers that tell us their soil organic matter levels have increased by one or two percentage points since they began using cover crops at the rate of 0.1 – 0.2 % per year. Whatever problem your soil has, odds are that a higher level of soil organic matter will fix it.
Increased Microbial Activity
All that extra residue and all those extra root exudates lay out a buffet table for soil microbes, of which 99% or more are extremely beneficial. These microbes can perform all sorts of beneficial functions, just as the system was designed to do.
Improved Soil Aggregation And Aeration And Reduced Soil Compaction
The soil microbes that feed on root exudates and form soil organic matter also produce biological glues that improve soil aggregation. Once a soil is aggregated into little balls, both air and water have pore space needed to freely flow through the soil, reversing the problems caused by soil compaction. This allows the development of a deep root system that can efficiently take up both water and mineral nutrients.
More Favorable Soil Temperature
A good mulch of cover crop residue or growing cover crop can keep soil cooler in summer and warmer in winter. On a hot day in summer, this may be as much as 60 degrees F difference between a field in a growing cover crop versus bare soil. When a soil temperature exceeds 140 F, microbial life is killed and the soil collapses and becomes rock hard.
Many cover crops are legumes, which are known to harbor bacteria on their roots which can pull nitrogen from the atmosphere and put it into biologically available forms. This contribution can be substantial. There are also many free-living nitrogen fixing microbes that live on root exudates which can make atmospheric nitrogen available as well.
Improved Availability Of Nutrients
The ability of cover crops to take up unused nutrients at the end of a growing season and sequester them into biomass to be used again later when that biomass rots can dramatically improve the availability of nutrients over time. This is quite pronounced with phosphorus, as phosphorus fertilizer has a strong tendency to become tied up into unavailable forms over time if not taken up by a plant. Iron availability can also improve dramatically from cover crops on high pH soils. For more information on iron deficiency chlorosis, see our archived articles at www.greencover.com.
The increased microbial population created by cover crops may sound like a recipe for more disease pressure, but the actual effect is just the opposite. The vast majority of the additional microbes are beneficial or benign and serve as food for microbial predators like protozoans that consume pathogenic organisms that can cause plant disease.
Some cover crop species are known to suppress nematodes that prey on crop roots. Such species include mustards, sunn hemp, and sorghum-sudangrass.
Cover crops can be highly suppressive of some weed species. Rye, for example, is highly suppressive of pigweeds and marestail, while oats are known to suppress kochia. The mechanisms for this are discussed in the video “Innovations in Controlling Pigweeds” on our YouTube channel.
Few species of wildlife are benefitted by large areas of bare, tilled ground. Even large areas of untilled crop residue offer far less benefit than the same acres with a green, growing cover crop. Green cover crops attract herbivores like deer and can also attract beneficial insects, or benign insects that can feed insectivorous animals like most birds. For more information, we recommend following Grant Woods on Growing Deer TV.
Attract Beneficial Insects, Including Pollinators
Many cover crops offer food and habitat for insects and other arthropods, including pollen and nectar for pollinating insects such as honey bees and wild bees which are essential for the pollination of many crops. Cover crops can be used to build populations of predatory insects, which can help prevent outbreaks of pest insects. Buckwheat, for example, is very useful for building populations of lady beetles and lacewings which can prevent aphid problems.
Raindrop formation requires hygroscopic condensation nuclei to form. We used to believe that dust particles were the primary condensation nuclei, but now we realize that it requires a HUGE amount of atmospheric moisture for soil particles to trigger rain. More effective condensation nuclei include pollen grains, fungal spores, bacteria that populate plant leaf surfaces, and volatile organic carbons produced by plant leaves. What do all of these have in common? They are all produced by plants or from plants. Replacing bare, tilled soil with growing plants (like cover crops) over a large area has been shown in recent scientific research to not only increase rainfall but also to reduce summer temperatures.
It Makes Farming Fun Again!
Last but certainly not least, growing cover crops puts the fun back in farming. How miserable is it to have a farm covered in gullies and blowing dust? How depressing is it to see soil quality decline more and more each and every year? Now imagine how much more enjoyable it is to have a farm teeming with life, a farm that absorbs rainfall, a farm that is constantly green and covered in blooming flowers, with soils that are constantly improving? Ultimately, how comforting is the knowledge that the little place on earth for which you have been granted temporary custody is going to be better when you leave it than when you received it?
THIS ARTICLE CAN BE FOUND ON PAGE 12-13 OF THE SOIL HEALTH RESOURCE GUIDE: VERSION 9