Diferentes usos da terra em ambiente semiárido: impactos sobre parâmetros ecológicos

Abstract

Throughout the development of civilizations, different practices for managing natural resourceshave been used, causing diverse impacts on ecosystems. In the Brazilian semiarid region, theintensification of land use change occurred with the introduction of livestock farming anddryland agriculture, with the cultivation of short-cycle species. However, with technologicaladvances, water bodies were used to irrigate fruit trees that have high added value. Theconversion of the Caatinga into different agrosystems, mainly monocultures, causes impacts onecological interactions and natural resources. Thus, the objective of this study is to analyze howland use change is impacting ecological parameters in a semiarid environment. The study wascarried out in ten land uses to determine total plant biomass, root:shoot ratio, distribution of theroot system along the soil profile, C and N stocks, interactions and C concentrations andnutrients in the soil, and the effects of the soil and climate variables on soil fauna. Mango hadthe highest aboveground and root biomass: 34.2 and 91.3 Mg ha-1. Preserved caatinga wassecond in aboveground biomass: 25.1 Mg ha-1, compared to 9 to 14.1 Mg ha-1 for open caatingaand permanent crops and 3.0 to 11.8 Mg ha-1 for grasses and annual crops. Preserved and opencaatinga, annual crops and forage cactus had root:shoot ratios below 1, while the other systemshad ratios > 1, especially mango (2.7). Most systems had roots concentrated in the 0-15 cmlayer. Although irrigated crops can accumulate more biomass than native forest, replacementby mangoes led to a severe depletion in soil C and N stocks, and all other systems also lost soilC and N. The shallower roots of buffel grass and forage cactus led to losses of C (7 and 18%)and N (7 and 20%, respectively) and accumulations of P, Ca, and Mg in deeper layers. Irrigatedcrops reduced soil C and N stocks. The use of fertilizers in bean and grapevine crops increasedsoil P and K stocks. The activity of detritivores and predators was predominant in the 0-20 cmlayer (monoliths), while the abundance of herbivores and microbivores was greater at the soilsurface (traps). Irrigated agricultural areas presented greater abundance of soil fauna and acommunity structure different from native forest and pasture, due to the continuous availabilityof water. Knowledge of ecological processes at a local scale in semiarid environments allowsthe definition of soil management strategies, such as incorporation of legumes in plantedpastures, increase of organic residues, mainly in mango crops, and maintenance of soil fauna inagroecosystems. These strategies can reduce the negative impacts of land use change in semiarid environments and promote greater sustainability in food production.