Fluxos de energia, água e CO2 em cultivo de cana-de-açúcar por métodos micrometeorológicos

Abstract

The understanding of biophysical processes that occur between the crops and the atmosphere is essential for the adoption of appropriate management practices, with a view to increasing yield. This work aimed to evaluate the variation of radiation, energy and CO2 balance components in sugarcane cultivation in the Coastal Plains of Alagoas, Brazil. Micrometeorological measurements were made from Jun 07 to Nov 17, 2013, in a commercial area of sugarcane (RB 867515 variety), plant cane cycle, with planting on 26 Mar, 2013. The determination of the latent (λE) and sensible (H) heat fluxes and net ecosystem exchange (NEE) were made by the eddy covariance method (EC). The radiation balance components were measured by a net radiometer installed above the plant canopy. In addition, λE was estimated by Bowen ratio – energy balance (BREB) considering two approaches, the first with estimate of the air temperature gradient on the two levels and the second using the surface temperature form measurements of the net radiometer (SBREB). λE was also estimated residue of the energy balance from the H determinations by EC (ECR), by modification of the BREB (MBREB), which combines the BREB with EC determinations, and the approach proposed in the FAO 56 Bulletin. The cloudiness conditions were determined from the clearness index (Kt), calculated from the relationship between global solar radiation (Hg) and at the top of the atmosphere (Ho). From the results, it was observed that the albedo and the relationship between the net radiation (Rn) and Rg and long wave balance (BOL) and Rg were not influenced by the cloudiness conditions. During the measurement period the most of the available energy at the surface (63%) was designed for the evapotranspiration process. The diurnal variation of the energy balance components was affected by cloudiness conditions and water available, with an available energy divided almost equally between E and H during dry season. In the relation λE estimation methods, the BREB has better agreement with determinations by EC, followed by ECR. The FAO56 and MBERB methods showed less agreement with EC. The diurnal variation of the NEE followed the course of radiation, with higher quantum efficiency under partly cloudy sky. The daily totals of NEE were affected by cloudiness conditions and water available.