.:: Lao Knowledge Base on Conservation Agriculture ::.
Live or dead (straw) plant mulch provides permanent soil cover. Residue from the previous crop can be left on the soil or cover plants can be sown (row or relay intercropping). To avoid competition with the main crop, the cover is subsequently dried (mown, crushed or herbicide treated), kept alive or potentially controlled under the crop canopy by a low-dose herbicide treatment. Then the biomass is left on the surface, not buried. Finally, seeds are sown directly in the residual plant cover after opening a hole or furrow with an adapted seeder (manual cane planter or stick). Cover plants are selected according to their complementarity with the main crop, their possible uses (food for humans or livestock), but especially their soil fertility enhancement potential. They are carefully selected to emulate the function of forest ecosystems—they must provide quick biomass production and have a root system that can reach deep groundwater supplies. These plants act as ‘nutrient pumps’: - Their powerful root systems help to structure the soil from the surface to deep horizons, to avoid compaction and maintain porosity conditions that are favorable for all crops in rotations. These species, with different root systems, tap different deep soil horizons. Water infiltration and air circulation are improved (macroporosity), along with water retention in the smallest pores (microporosity).
- Their root systems help to upwell and recycle nutrients located in deep soil horizons so as to make them more accessible for the next crop. This function is essential to reduce nutrient loss from the cropped ecosystem (groundwater polluting nitrates, sulfates and bases), to improve depleted soils and make them more productive.
Cover plants are selected according to their ability to perform their agricultural functions even under harsh cropping conditions (low rainfall, highly acidic soils, etc.). Moreover, they promote the development of high biological activity throughout the year, thus gradually strengthening the physical, biological and chemical qualities of the soil. Some of these plants may be able to disintoxicate the soil (e.g. Brachiaria sp. reduces aluminum toxicity). Maintaining total permanent plant cover on the soil provides the best and most efficient protection against pesticide pollution in all agricultural conditions. It thus provides a buffer zone where temperature and humidity are regulated, thus ensuring good growing conditions for crops, fauna and microflora.
