Dinâmica da água e nutrientes na solução do solo em um dendezal (Elaeis guineensis Jacq.) na Amazônia Central

Abstract

The knowledge of the hydric properties of the soil is a premise to quantify the water balance, which is given by the mass balance between inputs (rain and irrigation) and outputs: evapotranspiration, runoff and deep percolation loss. In western of Amazon, little is known about the dynamics of water and nutrients in the soil solution, especially in oil palm plantations. The studies were limited to certain areas of primary and secondary forests, agroforestry, degraded areas and pastures. Therefore, this study aimed to evaluate the influence of land use (oil palm plantation, dendezal in portuguese - DD and primary forest - PF) and temporal variations, in the soil water content and in the concentration of some minerals in the soil solution (SS). The experiment were installed in July 2013 and conducted until June 2015, in the experimental station of the Urubu River, CERU - Embrapa in Rio Preto da Eva. Amazon state - Brazil. It were installed two automatic soil solution station, to collected semi-automatically the soil solution in the DD and PF at three depths (20, 40 and 100 cm). Within the oil pal plantation it was also installed soil moisture sensors, soil temperature and soil matrix potential sensors in two depths (20 and 60 cm), and a rain gauge to record rainfall. In the border of the DD and near the PF plot was installed an automatic micro weather station with hourly evaluation of air humidity, and temperature, velocity and direction of wind, solar radiation, and precipitation. The micro station also recorded data soil water content, soil temperature and soil matrix potential with sensors installed at 20 and 60 cm depth. These data were used to estimate evapotranspiration and hydric balance of oil palm plantation and the dynamics of soil water with time. Soil samples with deformed and non-deformed structure were also collected and analyzed to determine chemical, physical and hydric characteristics of the soil. The soil of the two land use systems studies showed high water retention in the permanent wilting point (0.23 m3 m-3) and low available water (0.11 m3 m-3). Regardless of the depth, the pH of the soil solution in the two areas has a cyclic pattern to become more acidic during the rainy season. The electrical conductivity indicated leaching and nutrient losses in the periods of greater precipitation in DD than in FP. K+ is the cation with the highest movement in the SS DD and Al3+ in FP. Ca2+ is present in higher concentration in the SS DD, followed K+, Al3+ and Mg2+. In FP, Al3+ is present in the highest concentration, followed K+, Ca2+ and Mg2+. Among the elements evaluated, the lower concentration in the soil solution both areas were Fe2+ and Mn2+. The average daily evapotranspiration of oil palm was 3.2 mm. Of the precipitated water, 45% was evapotranspirated by the oil palms and 15% was retained by the canopy and the stipe of the palm oil. The area has a deficit and water surplus of 13 and 1,407 mm per year, respectively. The volumetric water content observed at 20 to 60 cm depth indicates a high water movement with elevated infiltration rates.