Zona da Mata de Minas Gerais is characterized by steep slopes, weathered soils with low natural fertility and precipitation capable to sustain a forest vegetation. Most of the land owners are small farmers, who suffer the consequences of modern agricultural technology, which demands intensive use of the land, causing soil, water and nutrient losses due to erosion. One of the alternatives proposed for the reduction of the erosive losses is to implement alternative agroforestry systems. The objective of this study is to compare losses due to erosion in agroforestry systems established in small farms under conventional systems. The systems were established as experimental units of observation under the existing environmental conditions, using participatory methodologies. It was difficult to quantify erosion using conventional methodologies. The management dynamics used by the farmers hinders the use of methods that require permanent equipment. Besides, methods demanding isolation of sample areas cause border effects that disturb the results, when compared with the open systems used by the farmers. Thus, a water and soil collector was developed to overcome these limitations. The equipment is composed by a "board" that is inserted in the soil, coupled to a mobile gutter that sustains a bag. The water and the soil collected in the bag are quantified and analyzed. This device was installed in 25 observation units, 14 under conventional and 11 under agroforestry systems. The energy of the erosive events was calculated from pluviograms to estimate the annual potential losses of the systems. Data were collected in the 1998/1999 rainy season. The total losses of soil, organic matter and nutrients under the conventional systems, estimated for one year, were significantly greater than those under the agroforestry systems, indicating a greater ecological sustainability of the latter, proving that agroforestry systems are able to preserve natural resources, stressing the need to convert conventional systems into ecologically sustainable systems.
Land use; soil conservation; sustainability; participatory research
