Monitoramento da deficiência hídrica do meloeiro (Cucumis melo L.) com termometria infravermelha.

Abstract

A field experiment was conducted during the 1993 crop season (October 22, 1993 to January 13, 1994) in a private farm , Fazenda Sao Joao, located in the city of Mossoro-RN. The crop under study was melon (Cucumis melo L.) cultivate Gold Mine. The main objective of this study was to relationalize the use of water resources of this region for crop production. The experiment was divided into four plots, each plot measuring 8m x 100m. Each plot received a different irrigation treatment. The plot PN received the irrigation treatment identical to that adapted by the farm (which is based on the evaporation measurements of a Class A pan evaporimeter) and the other three plots received 90, 80 and 70%, respectively, of the irrigation amount applied to the plot PN. Canopy (Tc), dry (Ta) and wet bulb (Tw) temperatures; atmospheric pressure (Po); global (Rg), reflected (Rr) and net (Rn) radiations; crop ( r c ) and aerodynamic Oa) resistances and wind velocity ( W ) 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. The soil humidity was monitored by using a neutron probe and also by the use of tensiometers. The water deficit was analyzed using different moisture stress indices such as the stress degree day (SDD), the crop water stress index (CWSIi) proposed by IDSO et al. (1981) and the CWSIj proposed by JACKSON et al. (1981). The values of the SDD index for the plot P3 were higher than those of plot PN, particularly at the end of the experimental season. The values of the CWSIi presented a large variability during the season due to variations in the global solar radiation and the wind velocity. The results suggest that the irrigation of the melon crop should be administered when the index reaches a value of 0.3 for the prevailing local climatic conditions. The morphological analysis presented higher values of fresh and dry biomasses and leaf area for plot PN compared to those of plot P3. The fruit production of plot PN was also higher than that of plot P3, but the productivity of plot PI was the highest. It is concluded that a decrease of 30% of irrigated water was sufficient to change the morphological development and crop productivity.