Balanços de radiação e energia em um cultivo de melão.

Abstract

This work was a result of date analysis from field experiment conducted in a private farm, Fazenda Sao Joao Ltda, located in the city of Mossoro-RN, in the period from October, 1993 to January, 1994. Its objective was to evaluate the radiation and energy balance components for various subperiod of development and growing of an irrigated melon (Cucumis melo L) crop, as well as to study the crop water requirements for the semi-arid conditions of Northeast Brazil. The experiment was divided into two plots, each one measuring 8m X 100m. Each plot received a different irrigation treatment. The plot PN received 100% the farm irrigation, obtained by the Class A pan evaporation and the other plot received 70% of the irrigation amount applied to the plot PN. Canopy (Tc), dry (Ta) and wet bulb (Tw) temperatures; atmospheric pressure (Po): global (Rsi), reflected (Rsr) and net (Sr) radiation; soil heat flux (G); crop (rc) and aerodynamic (ra) resistances and wind velocity (u) data were collected during the growing season of the melon crop. The canopy temperature was monitored by an infrared thermometer and a steady state porometer was used to measure the crop resistance. Leaf area, fresh and dry biomass were measured weekly. The morphological data showed higher values of fresh and dry biomass and leaf area for plot PN as compared to those of plot P3. It is conclued that a reduction of 30% in irrigatation water was sufficient to change the morphological development and crop productivity. The available net radiation throughout the crop growing season was 6 1% of Rsi. The components of the energy balance were significantly affected by the crop water stress conditions. Energy (LE) used in the evapotranspiration was found to exceed net radiation considerably. LE represented, in the average, 107% of Sr. Otherwise, the sensible heat fluxes (H and G) were 11% e 4% of Sr, respectively. Shortwave reflectivity (p) varied from 0.18 at the beginning of the growing season to 0.23 in the subperiod of fruit development with pronounced daily fluctuations, particularly after irrigations.