Influence of land use changes on soil physical, chemical and biological atributes in a family farming settlement in Eastern Amazon, Brazil

MIGUEL COOPER; SELENE CRISTINA DE PIERRI CASTILHO; JOSÉ CAMILO BEDANO; DOMÍNGUEZ, ANAHI; LAURA FERNANDA SIMÕES DA SILVA; MARIANA NASCIMENTO DELGADO OLIVEIRA

Viena

Congreso; EGU General Assembly; 2014

Soil knowledge and the changes in its attributes due to land use modifications in the Amazon region is importantfor decision making by family farmers. These farmers have to choose sustainable land use management practicesfor their survival in the region and, for soil and forest conservation. The study area is located in the Piranheira PraialtaAgroextrativist Settlement Project in the county of Nova Ipixuna, Pará, Brazil. The objective of this researchis to understand the relations between soil physical, chemical and biological attributes, and how these relationschange with modifications in land use. This information is important for defining best management practices forfamily farming in the region. Two toposequences were chosen, one under native forest and the other under pasture.40 cm pits were opened with five replicates in three landscape positions (upslope, midslope and downslope).Sampling periods were July/2012 (dry season); January/2013 (beginning of rainy season) and march/2013 (rainyseason). Samples were taken for soil particle size analysis, bulk density, particle density, moisture, porosity, waterretention, chemical, litter dry matter and macrofauna analysis. Statistical analysis techniques were performed uniand multivariate. No significant differences were observed in the particle size distribution of the studied soils. Thesoils presented sandy surface horizons with an increase of clay in depth in both land use systems. Soil bulk densityvalues were higher in the surface horizons and, in general, in the pasture toposequence. Differences were alsoobserved in the soil moisture content and litter dry matter which were higher under the native forest, and in the pHand organic matter values which were higher in the pasture. Higher water retention capacity was observed in thesurface horizons of the forest when compared to the pasture, corroborating the higher values of macroporosity observedin the forest soils. Due to higher moisture content, litter dry matter, water retention capacity and macroporespresent in the soils under native forest, a higher diversity and richness of macrofauna species was observed in theforest soils when compared to the pasture. Apart from the higher diversity, exclusive species and individuals with alarger body diameter were also found in the forest. A more detailed analysis of the earthworms, indicates a higherquantity of individuals under pasture, but these have smaller body diameters than the individuals found under theforest. The presence of individuals with larger body diameters influences the development of macropores in theforest surface horizons. Analyzing the influence of macrofauna on the different soil attributes, few changes wereobserved in the superficial horizons in relation to soil bulk density and total porosity in both land use systems. Onthe other hand, differences in the size and distribution of pores by the macrofauna were observed. These changesinfluence directly the soil water dynamics altering, sometimes irreversibly, the soil functioning in different landuse systems.