Pulsos pluviométricos na forma de orvalho e umidade do solo em duas coberturas vegetais em floresta tropical seca

Abstract

In semi-arid environments, a complete understanding of the temporal distribution of rainfall and its influence on soil water dynamics is essential for understanding hydrological processes at the level of watersheds. In this segment, the objective was to investigate the spatial and temporal dynamics of soil moisture in a toposequence of two watersheds and whether dew contributes significantly with moisture in the surface layer of the soil to the point of minimizing the effect of stress plants with predominant absorption roots in the surface layers. The experiment was conducted in two watersheds inserted in the phytogeographic domain of the caatinga, in the Alto Jaguaribe basin, in the municipality of Iguatu, South Central region of Ceará, with areas of 2.06 and 1.15 ha for the caatinga in regeneration (CReg) and the raleada (CRal), Respectively. To study the humidity, both basins were divided into three stretches, medium and high low. To verify the variability of moisture in different parts of the basin, random soil samples were collected daily in aluminum cans, three of which were collected in each stretch, totaling nine collection points in each basin. Soil moisture was determined by standard or gravimetric method. The dew study was carried out only at CReg, from Jun/2019 to Aug/2019. Soil moisture and dew were measured by four capacitive moisture sensors, installed at depths of 5 and 10 cm, with a reading interval of 1 minute. The results indicate that the difference in soil moisture was clearly affected by vegetation cover, providing higher values and a longer time interval in The Ral C in relation to CReg. The low stretch was the only one to present statistically significant difference in both basins. Precipitation was fundamental in moisture variability, but its distribution in the stretches was affected by topography. The increasing correlation value between humidity and previous precipitation in the last 5 days PPT. ANT.5 indicates the low decay rate of soil moisture. Studies on dew proved that during the study period, soil moisture increments were recorded at night at both depths. The increase in humidity during the night period was statistically significant in the months of June to August at depths of 5 and 10 cm. The average contribution of dew to soil moisture is 12.1 and 19.2 mm month-1, which represents 16.5 and 26.1% of the total annual precipitation. These results show the importance of dew for water availability and caatinga species in the months of water deficit.