Caracterização hidrológica e hidrossedimentológica em bacia hidrográfica sob diferentes manejos do solo no semiárido

Abstract

Semi-arid region of the Brazilian Northeast is marked by strong uncertainties regarding the occurrence of rainfall. In addition there has been an increase in degraded areas in recent years due to the intensive soil use and the lack of conservation practices adaption. In this perspective, it is necessary the understanding of the erosive processes in different spatial scales of measurement, as well as the influence of alternative coverage of the soil and the way the seeds of the vegetation are displaced. In this context, the present study aims to evaluate the importance of the use of mulch and nonconventional oilseed perennial species, moringa (Moringa oleifera Lam.) and neem (Azadirachta indica A. Juss.) for soil erosion control in experimental plots with different lengths, as well as the factors that influence the displacement of the seeds of these species by surface runoff. The study was carried out in the field under natural rainfall and in the laboratory under simulated rainfall (seed displacement analysis). In the field, the study was carried out during the years 2016 and 2017 in the representative basin of Mimoso, located in the municipality of Pesqueira-PE. The study area was composed of nine rectangular erosion plots with 2 meters wide, being distributed in three plots with lengths of 1; 10 and 20 m. The following treatments were adopted: presence of oleaginous; oleaginous + mulch and bare soil. The variables monitored in the field were: precipitation, surface runoff, soil losses, soil moisture, soil temperature, morphological characteristics of oleaginous plants (plant height and stem diameter). In the laboratory, the effects of seed morphology, rainfall intensities, precipitation patterns and surface slope on the transport of moringa and neem seeds were investigated. Laboratory tests were performed with 27 seeds of each species distributed on the soil surface of the bare soil treatment and or the soil with mulch, using a rain simulator and a rectangular earth channel. Different intensities (45-270 mm h-1) and patterns (uniform, advanced and delayed) were simulated on a variety of surface slopes of 10, 30, 50 and 70%. In erosion plots with 1 m in length, regardless of the soil cover, runoff and soil loss as were reduced larger that at the plots of 10 and 20 m in length .The plots of 20 m in length represented better the heterogeneities of the system, relief and erosion processes. The development of the vegetal tree structure of the oleaginous reduced the impact of the raindrops on the soil, which produced smaller losses of water and soil when compared to the bare soil. In the plots under laboratory simulated rainfall, seed displacements and losses by runoff increased with rainfall intensity and surface slope, and decreased with mulching. This study highlights that the application of mulching as a technique of erosion control and the use of heavy and flat seeds contribute to restore vegetation on steep slopes highly prone to soil erosion.