ALVES, A. V.; ALVES, Adriani Vieira.
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.
