African Organic Agriculture Training Manual: Soil Fertility Management
Learning targets for farmers: 1) Understand that soil fertility management is neither limited to the addition of mineral fertilizers nor to increasing crop yield alone. It consists of protecting the soil and enhancing the organic matter content as well as biological activity in the soil to encourage optimal nutrition, water supply and health of plants and increases consistency of yields. 2) Know the tools and approaches for organic soil fertility management and be able to combine them in an appropriate way so as to correspond to local conditions and combat soil degradation.
Fertile land and sufficient water are vital for sustaining agriculture and livelihoods. Productivity of land, however, has been decreasing with the increasing intensification of agriculture. Though there are other constraints, the intensification of agriculture is a major factor contributing to the recurrent cycles of famine in many African regions. Land degradation occurs in different forms on various land use types:
- On cropland, soil erosion occurs through: water and wind; chemical degradation – mainly fertility decline – due to nutrient mining and salinity; physical soil degradation due to compaction, sealing and crusting; biological degrada¬tion due to insufficient vegetation cover, decline in soil organic matter; and water degradation mainly caused by increased surface runoff (polluting surface water) and changing water availability due to high evaporation.
- On grazing land, biological degradation occurs through loss of protective vegetation cover and valuable species. As a result, alien and ‘undesirable’ species settle in the soil. Physical degradation of soil results in widespread and severe water runoff and erosion.
- On forest land, biological degradation occurs through: deforestation; removal of valuable species through logging; replacement of natural forests with monocrop plantations or other land uses (which do not protect the land), which have consequences including biodiversity loss and soil and water degradation.