How Cover Crops Improve Soil Health
ST Biologicals
Crop consultants who work with you to restore the fertility of your soil and increase farm profits.
Why is everyone talking about cover crops? We know everyone’s concerned about topsoils and soil health in general. The economics of farming require attention to soil to get good yields. But soil does much more than germinate seeds and keep plants nourished.
Soil health is usually defined as the capacity of soil to function as a living ecosystem that sustains plants, animals. and people.(1) But there are many links between soil health and the nutritional value of the food produced.
Cover crops play a crucial role in maintaining soil fertility necessary for beneficial microorganisms and the efficiency of the entire nutrient cycle. Living roots are important for soil health and human health.
We will explore how cover crops can significantly enhance soil health.
The Importance of Soil Health
Healthy soil plays an essential role in crop production and ecosystem stability. The long-term economic viability of a farm or ranch is tied to the quality of the soil. Cover crops play a role in farming practices that improve the soil. Traditional agricultural practices negatively impact the viability of a farm through soil degradation, erosion, and nutrient depletion.
How do you incorporate cover crops into your existing farming or ranching practices? You start by planning and asking yourself some questions.
1. What is your goal?
2. What is your location?
3. What was your preceding crop?
4. What crop are you following with?
5. What is your cover crop planting window?
6. What is your cover crop termination method?
Answer these questions and you’ll be well on your way to more fertile soil, less disease, fewer insect pests, and good yields.
What Are Cover Crops Anyway?
Cover crops are grown for the protection and enrichment of the soil. But what does that mean? And how does that fit into a row crop farm?
Essentially, any plants growing in a field that aren’t harvested are cover crops. But that could also include weeds. And often weeds are beneficial for rejuvenating the soil on a field. But we’ll discuss plants planted for specific soil and microorganism benefits.
The Diverse Range of Cover Crops
No matter what the season, there are cover crops that create optimum soil conditions in your fields and pastures. Cover crops can accomplish a great many things in your fields. It’s important to plan before you plant.
In the past, you may have planted cover crops only between cash crop harvests. But when you interplant covers with cash crops you get double duty from the covers. They suppress weeds while maintaining soil moisture. Cover crops shade out weeds and their canopy creates a nice umbrella shielding your soil from the intense heat of the sun.
Prior to planting in the spring, many cover crop species are quick to germinate and prepare the soil for cash crops. Field peas are fast-growing legumes that suppress weeds and fix nitrogen. Oats and annual ryegrass grow fast, decrease erosion from spring rains, and build up biomass in your soil.
In the summer, either between crops or interplanted with a cash crop, summer cover crops are well worth the extra effort. Both buckwheat and pearl millet suppress weeds and improve soil aggregation. Millet is becoming very popular because it can handle drought and fix nitrogen.
After harvest is a traditional time to plant covers. Hairy vetch, daikon radishes, and many clovers will improve water infiltration while keeping weeds at bay. Vetch and clovers also fix nitrogen.
Many of these cover crops winter kill but the root growth and surface biomass protect your fields from winter erosion, acting as a living mulch. They also feed the beneficial microorganism communities so there is less real estate for pathogens come spring.
How Do Cover Crops Enhance Soil Fertility?
Different cover crops for different purposes. That’s why answering the questions above and planning are critical.
Legume cover crops fix nitrogen through a symbiotic relationship with rhizobia bacteria. The bacteria live in nodules on the plant roots Soybeans can fix up to 250 pounds of nitrogen per acre and perennial crops such as clover or alfalfa up to 500 pounds of nitrogen per acre. These plants need very little, if any, nitrogen fertilizer.
Adding nitrogen to a field of legumes that are already fixing nitrogen with the aid of soil bacteria will literally shut down the fixation process. Studies by New Mexico State University have found that yields will be low, even with nitrogen fertilizer, if nodules aren’t present. Nodules seem to help plants use nitrogen fertilizer more effectively. With good farming practices, your soil bacterial communities are allies in soil fertility, and less fertilizer inputs are needed.(2)?
Cover crops increase the efficiency of nutrient cycling. Soil biodiversity is important for crop yields. The stronger the microbial community the more mineral nutrients in the soil are available for plant intake.
Nutrient Cycling and the Role of Cover Crops
Some nutrients, such as nitrogen, are very mobile in soil. Nitrogen leaches rapidly out of soil with little organic matter or living roots. But deep-rooted cover crops, such as radishes and clovers, scavenge the deep soil layers for nutrients. They capture and store nutrients in their biomass until they’re terminated. The nutrients are then available to cash crops in plant-available forms.
Living roots of cover crops help improve soil structure, key to strong beneficial microbial communities. Soil microbes, earthworms, and other soil critters convert nutrients into plant-available forms. Soil community diversity leads to optimum plant growth.
Cover crops, or green manures, are a critical piece in soil health management.
Decrease Soil Erosion with Cover Crops
Bare fields are subject to water erosion by hard rains and snow melt. Winds blow topsoil from your field, taking with it beneficial soil microbes and plant nutrients. They usually end up in nearby lakes and streams, causing decreases in surface water quality. Algae blooms are on the rise.
The impact of a raindrop is incredible on a patch of bare soil. Some particles are dislodged while others are compacted. During a rain event, the drops can fall at velocities reaching 30 feet per second. They splash soil as high as 3 feet in the air. Those particles can land 5 feet away. In the process, the wind associated with the storm moves soil particles even further.(4)
This erosion process is diminished, if not stopped completely, with plant material covering the soil. Different cover crop species do this job better, but any plants are better than bare earth, including weeds. A study shows the raindrop soil displacement rate was 67 percent less falling on crop canopies than on bare earth.(5) When you decrease topsoil erosion with cover crops, you increase your nutrient retention. That’s money in your pocket.
Increasing Beneficial Microbes
When you’ve got healthy soil livestock (microorganisms) you’ll have to worry less about how to control pests. Beneficial microorganisms are plant allies in numerous ways:
1. They take up space in the rhizosphere and phyllosphere so pathogens don’t have a chance.
2. They activate a plant’s defense mechanisms to fight disease and pests.
3. Their movement improves soil structure for better root development.
4. They are actively creating humus.
Over 90 percent of all plants on Earth have symbiotic relationships with microbes. We usually think of soil microbes, but microorganisms are everywhere, and at all stages of a plant’s life – from seed to the next seed generation. Although the majority of microbes are found in the plant rhizosphere, a large amount are found on the plant leaves, the phyllosphere. (6)
Microbes found on plant leaves can intercept carbon compounds emitted from plants, take in ammonium pollutants, and impact the health of each plant. Having a strong colony of beneficial microbes in the plant’s phyllosphere results in less space for pathogenic microorganisms.
Beneficial microbes, especially mycorrhizal fungi, create a form of biostimulation to rouse a plant’s defense mechanisms when they sense pathogens.
Microbes lead very short lives. Eaten by larger microorganisms or dying natural deaths. Many are decomposers, creating humus from organic matter. Earthworms, one of the soil critters we can see with the human eye, move through plant root zones creating tunnels coated with worm castings. This improves soil structure for better plant root development.
Agricultural fields are bacterially dominant because of the traditional use of pesticides, fungicides, and tillage. The use of herbicides to terminate cover crops decreases the value of your conservation practices. Using a roller-crimper to terminate cover crops is a management practice that maintains soil microbes, particularly mycorrhizal fungi. A more balanced bacteria/fungi ratio creates a better environment for optimum plant growth, crop yield, and long-range soil health.
The Long-Term Environmental Benefits of Cover Crops
Incorporating cover crops in a multi-year crop rotation system has far-reaching benefits. Besides decreasing the erosion of topsoil, when you add cover crops to your farm production system, you begin building topsoil, and at a rate greater than nature can do alone. As climate change issues such as drought and flooding occur with increasing frequency your farm will benefit from the ecosystem services supported by cover crops.
Weed management is one benefit of covers that isn’t given enough press. Using management practices that use fast-growing cover crops gives slower-growing cash crops the benefit of greater water infiltration and nutrient retention. Especially beneficial when germinating and at grain set.
Legumes, which fix nitrogen, reduce your nitrogen fertilizer needs. Cover crops, interplanted with cash crops, keep the soil covered at all times so less evapotranspiration occurs.
Of course, a soil test is an important first step. Once you get that soil health assessment, and you need to know more than just the NPK and soil pH. You need to know your micronutrient and microbe profiles.
Armed with that information you can look at cover crop seeds. Good soil fertility management leads to healthy crops. At ST Biologicals, we are passionate about soil health. Cover crops have been proven to improve soil structure, increase microbial community diversity, and create better overall soil function.
Contact us to find out how your farm or ranch can benefit from the power of cover crops.