Green manure/cover crops and crop rotation in Conservation Agriculture on small farms
The objective of this publication is to offer a reference material for extensionists, professors, agronomy students, technicians in general, and for farmers themselves. Through information that is up-to-date and richly illustrated, it strives to facilitate the adoption and diffusion of No-Tillage, the use of green manures, and the practice of crop rotation on small farms. The publication describes the principal species of green manures and, at the same time, informs in detail how to insert green manures into small farm production systems according to soil fertility and major crops. It also deals with the residual effect of green manures on main crops and analyzes the economic implications of these practices.
Soil degradation on small farms in the Eastern Region of Paraguay is the principal cause of a continuous decrease in crop production. The consequences of this are reduced economic income and increased poverty among rural families.
One of the principal reasons for this fact is the continuous utilization of inadequate methods of soil management, including the burning of vegetative residues, excessive tillage, and monoculture. The exposure of bare soil to climatic agents (high temperatures, torrential rains) accelerates the soil degradation process, as they cause excessively rapid decomposition of biomass and favor the erosion and leaching of nutrients.
The decrease in productivity is closely tied to a decline in the levels of soil organic matter. In poor soils, it is organic matter that determines the improvement of physical aspects, water retention, and biological activity, as well as the storage and slow release of nutrients. These aspects are most significant in sandy soils. Therefore, in order to maintain soil productivity in agricultural systems on small farms (where chemical fertilizers are normally not used) biomass is shown to be an essential element, due to the fact that it permits nutrient recycling and controls the microbial population that maintain favorable soil properties. One great difficulty in relation to the maintenance of biomass in tropical and subtropical climatic regions is that it breaks down much more rapidly than the capacity of conventional agricultural systems to replace it.