In my last article , we dealt with the many benefits of cover crops and how they can really help improve soil health, soil structure, nutrient availability especially phosphorous , and water infiltration and moisture holding capacity.
These are some of the most important yield destroyers in African soils. Indeed, as I write this, I am pulling up my lawn to plant a season of daikon radish and lucerne, to soften my soil, and remove the soil compaction and feed my pigs. We eagerly wait for the rains to start. Improved Soil Fertility β cover crops grown to improve soil fertility are known as green manure crops. Cover crops with shallow fibrous root systems, like grasses, build soil aggregation and structure in the topsoil, reduce surface capping and compaction , and improve water infiltration.
Cover crops with deep tap roots break up compacted layers and bring subsoil nutrients up to the topsoil. Deep rooted crops are also effective at bringing leached fertilisers up to the topsoil. Some cover crops are mycorrhizal, like sunflower. This means they form a symbiotic relationship with mycorrhiza fungi. Mycorrhiza is very effective at solubilizing phosphorous and other nutrients and binding them in an organic form which is much more available to the cover crop and following crops.
In addition, mycorrhiza take the sugars formed from atmospheric carbon dioxide via photosynthesis of the cover crop and produce chitin and glomalin, one of the most efficient systems of sequestering stable soil carbon and incredibly effective at improving soil aggregation and moisture holding capacity. Years of ploughing the soil, monocropping and applying herbicides and fungicides means that many soils lack this essential soil organism. For improving soil carbon quickly concentrate on cover crops that produce a huge dense volume of roots.
Most effective here is a cover crop mix of different species that fill the whole soil profile. When terminating the cover crop keep the roots in place. Roots are much more effective at building organic matter than the above ground biomass. And as the roots decay they create soil channels that water and proceeding crop roots can follow, deep down into the soil. Nitrogen scavenging cover crops are useful if you have a high soluble nitrogen level in your soil for e.
