Organic matter management in family agriculture of semiarid Paraiba, Brazil

Soil fertility in low-input agriculture on weathered soils in NE Brazil largely depends on organically held nutrients. Under traditional shifting cultivation, soil organic matter is regenerated during a bush fallow period, followed by mineralisation and nutrient liberation in the cultivation phase. When land becomes scarce, shifting cultivation is abandoned and land degradation may result from continuous use. Farmers then adopt various strategies to maintain organic matter and fertility levels on productive parts of the land, often by biomass, residue or manure transfers. Levels of organic matter and fertility along the cycle of shifting cultivation have been reported in the literature, but the extent, magnitude and importance of managed organic matter movement within and between farms and land use units remain largely undocumented. We here present several models for the movement of organic matter in and between different management units. The presence of these fluxes was observed and documented qualitatively with the help of farmers on small holdings in a region of transition from subhumid to semiarid climate in NE Brazil. Principal flows were identified associated with the transport of produce and residues from production fields to home gardens, corrals and homes, but also back from areas of concentration to fields under high value crops. Fluxes depend on crop value, farm capitalisation and the structure and development of the farm family. We conclude that these fluxes are significant for the function of different land units and suggest that they should be quantified systematically to provide an understanding of the sustainability of continued landuse in regions traditionally used under shifting cultivation.