By Jan-Hendrik de Villiers
The five rules for maintaining healthy cover crops are permanent organic coverage, sustained and active root growth, diversification of cover crops, minimal soil disturbance, and including a livestock component.
Dawie du Plessis, Agricol’s sales manager, stated earlier this month at Landbouweekblad’s conference on sustainable agriculture in Moorreesburg that all five rules for soil health in cover crops are equally important for making a significant difference in farming. He says a farmer will struggle if he follows only two of the five steps.
1 Permanent organic coverage
The primary purpose of maintaining permanent organic coverage with cover crops is to protect microbes that supply 85% to 90% of the nutrients to plants. These microbes include bacteria, fungi, and algae and provide essential nutrients such as nitrogen, carbon, and phosphate.
“The bacteria or fungi are responsible for extracting nutrients from the soil,” he said, explaining that as the soil quality decreases, the nutrients become less accessible to plants.
“The plants cannot obtain it themselves. This is where the microbes must fulfil their role.” Up to 70% of the microbes in poorer soil may be dormant.
The microbes can be protected by lowering the temperature of the soil, reducing evaporation from the soil, and getting better water infiltration into the soil.
“The ideal soil temperature for any crop is between 18°C and 30°C,” Du Plessis says.
2 Sustained and active root growth
Although coverage is essential, there must still be something that grows- in this case, the active growth of the roots. This is one of the crucial ways carbon enters the soil without needing to transport or plough anything in.
Green plants serve as conduits for carbon dioxide in the air. The plant then converts the carbon dioxide into sugar through photosynthesis and releases it through the roots.
Du Plessis states that 50% to 60% of the sugar (glucose) is secreted into the roots for the microbes, while the glucose still retains carbon, water, and oxygen.
“Then you get the continuous pumping of carbon into the soil naturally,” he says.
Therefore, the plant does not need to grow to reach the nutrients, as sugars are supplied through symbiotic cooperation from the roots to the microbes, after which the microbes provide nutrients, such as phosphates and potassium, to the plant.
3 Diversification of cover crops
By diversifying crops, various root types at different soil depths can secrete different forms of glucose to attract a variety of microbes.
“A legume will not want to attract the same microbe or microbes as, for example, a wheat or oat plant. We’re looking for that balance between the microbes in the soil.
“We don’t just want roots within the top 20 cm; we want them to reach up to a meter deep. This way, you achieve the maximum variety of roots per m³, each attracting its own microbes and quickly restoring balance to the soil.”
4 Minimal soil disturbance
“If the soil is disturbed slightly, it will not greatly affect the symbiotic relationship between the plant’s roots and the microbes but avoid disturbing your soil unnecessarily and without good reason. You don’t want the air particles in the soil to collapse. You also want to keep the carbon from escaping, and you don’t want the microbes to die.”
If the soil is kept minimally disturbed, a farmer preserves the microbial life from one season to the next.
When certain roots die and decompose, they release carbon that microbes absorb. When the next crop is planted, everything is already accessible in the primary root zone for the young plant, du Plessis explains.
5 Livestock factor
The taller a cover crop grows, the more moisture is drawn from the soil. When animals are used to maintain shorter cover crops, less moisture will be drawn from the soil.
“The animals can provide a return on your investment. In other words, they’ve gained some weight, and ultimately, you receive some money back.”
He says that livestock can break down old residues through their digestive systems, making them more readily available for your next cash crops.
Following this rule, a rapid carbon build-up will occur due to the roots dying and regrowing.
Du Plessis says this is the second fastest method of getting carbon into the soil. When the plant’s above-ground parts are grazed, the roots below the surface will die in balance.
“If two-thirds are grazed above, two-thirds [of roots] will die below the ground.”
Carbon is thus secreted “without you having to do anything,” and no tractors need to be started. If the growth of the cover crop is regulated, the process will be kept in check.
If animals are not an option for a farmer, an alternative method is to cut the cover crops.
