Cover crops support soil health by increasing soil carbon – organic matter – which stimulates microbial activity and improves soil structure. By Anna Mouton
The impact of cover crops on soil health was discussed at a workshop facilitated by the World Wide Fund for Nature (WWF) held at Oak Valley in Grabouw in August.
Ivan Jansen van Rensburg from Barenbrug described eight soil-health benefits of cover crops: sequestering carbon, supporting microbes, suppressing diseases, fixing nitrogen, suppressing weeds, preventing erosion, building structure, and improving aeration and infiltration.
Different cover crops have different strengths, so diversity is important. For example, radish roots muscle into the soil, breaking up compaction, enabling water movement. But Jansen van Rensburg pointed out that the finer roots of cereals are as useful as the large roots of radishes.
"A diversity of roots creates micro and macro pores in the soil for water and air," he said. "Deep-rooted cereals can also put carbon deeper into the soil where it is more stable than carbon located at the surface."
Legumes offer the bonus of nitrogen fixation – their dry matter typically contains 1.5 – 4.0% nitrogen. "This is relevant as the price of nitrogen fertilisers has skyrocketed recently," said Jansen van Rensburg.
However, he cautions that the amount of nitrogen supplied by legumes will depend on the variety and species of cover crop, as well as the amount of biomass it produces. "Growing conditions and how happy the plant is, as well as how successful the inoculation of rhizobium on the roots has been, will have a big influence on the amount of nitrogen fixed."Read More