Respiração do solo em áreas de caatinga e de pastagem no semiárido de Pernambuco

Abstract

Land use changes bring about alterations in the way in which the biophysical attributes of the soil are manipulated and by the actions underlying those manipulations. The Caatinga biome is the predominant ecosystem in the Northeast region, extending throughout the semiarid region. In this region, Caatinga is replaced by grasslands, which causes the loss of organic carbon in the soil. This loss of carbon can occur through the process of the soil respiration by the emission of CO2 into the atmosphere. Biochar is a carbon rich product with potential to improve soil physical properties, which can have effect in the soil respiration. Thus, the present work had the following objectives: a) to evaluate and compare soil respiration in Caatinga and pasture areas; b) to determine the variables (soil moisture and temperature) that influence this process and c: to evaluate the effect of biochar addition on soil respiration in Caatinga and pasture areas. The work was realized in two experiments: one in field and another in laboratory. The activities of field were were carried out in two areas, one at the Buenos Aires Farm, Preserved Caatinga (CP), and the other located at Farm Lagoinha, cultivated with degraded pasture (PD). Both properties are located in the Municipality of Serra Talhada - PE, a micro-region of the Pajeú Valley. In order to monitor soil respiration (Rs) in the Caatinga and pasture areas, an infrared gas analyzer (IRGA, model LI-6400-09) was used, the measurements were divided into three periods according to the precipitation distribution (S), transition period (T) and rainy season (U). Soil respiration (Rs) was higher in the Caatinga during dry and transitional periods, and in the humid (U) period, Rs was statistically similar in the preserved Caatinga (CP) and degraded pasture (PD). In the wettest period, the highest values of Rs occurred, being 4.15 μmol m-2 s-1 in the Caatinga (UCP) and 3.10 μmol m-2 s-1 in the pasture (UPD). In the relation between Rs and soil temperature, it was observed that in the Caatinga a negative linear relationship was observed, in the relation between Rs and soil moisture in the Caatinga, it was linear positive and significant, indicating that with the increase of soil moisture, an increase in Rs. The soil used in experiment 2 was collected from the superficial layer (0-20 cm) at the Riacho do Papagaio farm, in the municipality of São João - PE. The experiment was conducted in a greenhouse, being arranged in a double factorial design with a total of 4 treatments (2x2), being 2 types of soil and 2 doses of biochar applied (0 and 20 t ha-1). Soil respiration (Rs) in Caatinga areas without biochar (C) ranged from -1.09 to 12.86 μmol m-2 s-1, while biochar ranged from -0.09 to 9.05 μmol m-2 s-1, for the grazing area without biochar at Rs ranged from 0.03 to 1.43 μmol m-2 s-1 and with biochar ranged from -0.09 to 5.54 μmol m-2 s-1. It was observed that the treatments where biochar were added had higher values of soil moisture and organic carbon, however the biochar had no effect on Rs. Thus, the practice of adding biochar to the sandy soils of the semi-arid region has the potential to mitigate land-use and climate changes.