Soil is more than the dirt beneath our feet. Soil is rich in biodiversity. According to Kathy Merrifield, a nematologist from Oregon State University, “one teaspoon can hold up to one billion bacteria, several yards of fungal filaments, several thousand protozoa, and scores of nematodes.” Unfortunately, soil is eroding at unprecedented rates. Professor John Crawford of the University of Sydney warns that “a rough calculation of current rates of soil degradation suggests we have about 60 years of topsoil left.”
But cover crops can help protect soil and prevent degradation.
According to the U.N. Food and Agriculture Organization (FAO) “cover crops improve the stability of the conservation agriculture system.” Cover crops are one of the most effective ways to make staple crops and soil their most productive while also enriching land for future use and providing biodiversity for the greater ecosystem.
The FAO also reminds us that with the Green Revolution of the 1960s, “the production model focused initially on the introduction of improved, higher-yielding varieties of wheat, rice, and maize. Fertilizers replaced soil quality management, while herbicides provided an alternative to crop rotations as a means of controlling weeds.” But today farmers are leading a resurgence of interest in cover crops and the concept of the sustainable agroecosystem.
Practical Farmers of Iowa is an organization of farmers promoting farmer-led agriculture beneﬁcial for land and people. They advise farmers, “Don’t farm naked” to highlight the benefits of cover crops. Practical Farmers of Iowa uses a Cooperator’s Program of on-farm research conducted by farmers to find effective solutions to contemporary agricultural challenges, and “transition to more sustainable and economically profitable systems.” The Cover Crop Variety Trial 2014-2015 experiments with and analyses a wide variety of cover crops in Iowa production systems.
Cover crops such as rye, alfalfa, and clovers are needed to protect soil from excessive rain and sun, provide organic structure, distribute nutrients, and limit harmful pests and weeds. They also provide economic benefits through reduced fertilizer needs, fewer problems with pests and weeds, and often, larger yields.
Cover crops are classified into legumes and non-legumes with each grouping having its particular applications and benefits.
Legumes like alfalfa, clovers, cowpeas, medics, soybeans, sunn hemp, velvet bean, and woolypod vetch are part of the pea family. Often referred to as green manure, leguminous cover crops can be tilled under and incorporated into the soil where their decomposition provides nitrogen, phosphorus, and other nutrients to subsequent crops. Legumes also help prevent erosion, add organic matter to soil, and attract beneficial microorganisms and insects.
Cereal grains, grasses, brassicas, and mustards make up the non-legume category.
The high carbon content of grasses and grains like barley, oats, rye, sorghum-sudangrass, wheat, spelt, and triticale leads to a slower breakdown of their organic materials. This biomass lasts longer and is effective at limiting weeds, especially when left on ground as mulch. Their low nitrogen content relative to legumes also makes them effective nitrogen scavengers, important for balancing soil that has become oversaturated with nitrogen. This leads to a higher all around nutrient extraction with less nutrients left over for the next crop. Buckwheat is particularly effective at drawing out phosphorus and calcium from the soil. Like legumes and most cover crops, grasses and cereals also help limit soil erosion.
Brassicas and mustards like arugula, kale, rapeseed, and turnips, while not legumes, are in between legumes and grasses regarding nitrogen content and rate of breakdown. They are effective pest controllers due to strong chemical compounds released during their decomposition process that are toxic to pests and weeds, while reducing the prevalence of disease in subsequent crops. Brassicas and mustards tolerate cold and drought well, have expansive roots, and serve as useful feed for grazing animals.
Following on traditional farming practices around the world, the Land Institute focuses on crops which are perennial, meaning they live all year, and are harvested multiple times, instead of just once before dying. The Land Institute believes in agriculture in harmony with nature. The complexity that perennials and cover crops bring to soil supports biodiversity and improves soil health. “This web of checks and balances, predator and prey that make up complex ecosystems make it difficult for any single species to dominate. Instead, a self-regulating equilibrium sets in.”
According to Sustainable Agriculture Research & Education (SARE), planting cover crops in between staple crops has a variety of economic and environmental benefits. SARE has released a report describing positive results from a survey of over 750 U.S. farmers on cover cropping practices.
Cover crop mixtures often involve combinations of legumes that are powerful nitrogen contributors with cereals and grains that are effective at drawing excessive nutrients like nitrogen out of the soil. These mixtures regulate the nitrogen content of soil causing grasses to thrive if soil is nitrogen rich, and legumes to flourish if the soil lacks nitrogen. Sorghum-sudangrass is effective at invigorating unproductive soil from the biomass it leaves behind.
Soil is a rich living system of organisms. Crops with different root lengths make soil richer by distributing water and nutrients across a greater area. Oats, radishes, rye, brassicas, and mustards have long root systems, while clovers and peas have shorter dimensions. Together they can help maintain a rich growth environment. Roland Bunch,a sustainable agriculture expert with Groundswell International, points out that intercropped cover crops can save farmers work, since they “shade out” weeds.
The legume medic has a particularly hard seed and is drought tolerant, beneficial characteristics for dry periods. Cowpeas and soybeans thrive in high heat environments, while spelt adapts well to the cold.
Woolypod vetch, as well as clovers and other flowering cover crops, are also able to attract bees that are needed to pollinate many fruit and vegetable crops. And cover crops like grasses and alfalfa provide a home for earthworms that make soil receptive to water and air while helping to distribute organic matter.
Traditional indigenous crop techniques have been documented by Roland Bunch, such as those using beans with rice in Vietnam and clover with maize in Mexico. “We know green manures and cover crops can sustainably maintain or improve soil fertility and productivity because they did so for millennia, all across the world.”
Groundswell International has partnered with Oxfam America to include cover crops as part of its training program for women farmers in rural Mali.
The mixture possibilities that can be applied to various situations, crops, and soils are endless. Sustainable agriculture practices like cover cropping can help fight dangerous food and soil problems, maximize productivity, and enrich land for future use.
“We must stop treating soil like dirt. We are dependent on our soil. It is everyone’s future.” – The Land Institute