Izabel Cristina de Luna Galindo

Relações solo-vegetação em áreas sob processo de desertificação no município de Jataúba, PE

Land degradation in semiarid regions is a result of natural processes that can be induced or intensified by man through the inadequate use of natural resources, resulting in the degradation of vegetation, soil and water resources. Aiming to relate vegetation and soil degradation processes in the Agreste region of Pernambuco State, soil and vegetation in twelve representative plots were characterized as preserved, moderately degraded and degraded environments in the municipality of Jatauba. To study the vegetation, plants were stratified in three layers or height classes: 3 - plants taller than 3.0 m, sampled in the total plot area (200 m2); 2 - plants with a height between 0.51-3.0 m, sampled in an area of 100 m2; 1 - plants with height equal to or less than 0.50 m, sampled in 18 miniplots of 25 x 50 cm. Soils were morphologically characterized in each plot and samples collected from each horizon for physical, chemical and mineralogical analysis. The vegetation of the 2nd stratum showed a great decrease in absolute density as a result of soil degradation intensity. Species with highest relative densities were: Neoglaziovia variegata (caroa) and Cordia leucocephala (moleque-duro) in the preserved area; Bromelia laciniosa (macambira), Aspidosperma pyrifolium (pereiro) and Caesalpinia pyramidalis (catingueira), in the moderately degraded area; and C. pyramidalis and Sida galheirensis (malva branca), in the degraded area. The soil properties of the Planosols that were strongly correlated with the preserved vegetation were the gravel contents in surface horizons, thickness of A + E horizons, and the concentration of organic carbon. The occurrence of soil crusting and erosion, as well as high percentages of exchangeable sodium was observed with greater intensity at the degraded sites covered by more sparse vegetation.

Humic Haplustox under different land uses in a high altitude environment in the Agreste region of Pernambuco, Brazil

The Garanhuns Plateau in the Agreste region of the State of Pernambuco, Brazil is characterized by humid climatic conditions due to orographic rains, unlike the surrounding semiarid region. These soils are subjected to intense agricultural use and are extremely important for the regional economy. This study was carried out in the municipality of Brejao in the Agreste region with the aim of assessing changes in humic Haplustox soils subjected to different land uses. Four plots with different vegetation covers (native forest, secondary shrubby vegetation (capoeira), traditional cropping system, and planted pasture) were selected, and samples were taken from a soil profile and four small pits surrounding it at each site. Physical and chemical properties were assessed, including aggregate stability, humic organic fractions, and a microbiological evaluation through determination of basal respiration, microbial biomass carbon, and metabolic quotient. The soils under study showed physical and chemical properties typical of a Haplustox, such as low nutrient content, low cation exchange capacity, and high levels of acidity and Al saturation. The total organic carbon (TOC) contents were high regardless of the type of land use. Aggregates < 2 mm were dominant in all the conditions under study. The TOC content was higher in the soil under capoeira, 43.91 g kg-1 on the surface, while 34.36 and 33.43 g kg-1 of TOC were observed in the first layer of forest and pasture soils, respectively. While the microbial biomass C (MBC) was greater than 700 mg kg-1 in the forest and pasture areas (in the 0-5 cm layer), and 588 mg kg-1 in the soil under capoeira, these numbers were not statistically different. In the cultivated soil area, there was a reduction of around 28 % in TOC and MBC contents. Agricultural activity contributed to degradation of the humic horizon, as can be seen from a significant decrease in the TOC and changes in the relative distribution of the humic fractions. In contrast, aggregate stability was not altered as a function of the different land uses; the soil under planted pasture and capoeira were similar to the soil under native forest. Humin was the most important humified fraction for C reserves, contributing over 40 % of the TOC in these soils.