Influência do tipo de arquitetura do dossel na absorção de radiação solar, na produtividade e na quantidade do fruto da mangueira.

Abstract

This research work was conducted at Mossoro-RN in 2001/2002 to devise alternatives for increasing the productivity and improving the quality of Tommy Atkins mangoes, based on the influence of crown architecture, solar radiation, and air temperature. To study the penetration of the solar radiation in the crowns it was utilized 30 trees which underwent crown thinning by different methods. Sensors were placed at selected sites for measuring the global, infrared, and photosynthetic active radiations inciding on the top and base of the crowns, as well as the reflected radiation on the crown top, besides the temperature near the fruits. Data were obtained at each time second through automatic data collecting systems. At harvest each tree crown was subdivided in quadrants and the fruits collected separately. The fruits were stored in cold chamber for color analysis and determinations of soluble solids content (SSC), titratable acidity (TA), and pH at zero, at 24 and 31 days post-harvest. The maximum albedos were provided by the 2V-thinned (19.7%) and pyramidal (19.2) architectures. Control, V-thinned, and 4V-thinned architectures did not differ significantly with regard to the albedo and the cup-shaped architecture was the least reflective. The amount of radiation that reached the crown base varied significantly depending on the crown architecture, 22.0% in the control to 65.0 in the cup-shaped. Short wave radiation inciding on the crown base in the cup-shaped architecture was threefold that at the base of the control. The infrared radiation inciding on the crown top averaged about 48.2% of the short wave radiation, while the reflected varied from 28.9% in the 4V-thinned to 34.0% in the pyramidal architecture. As the control architecture screened only 43.9% of the top-inciding infrared radiation, the V-thinned, cup-shaped, and 2V-thinned architectures allowed pass through 79.4, 74.3, and 70.3% of that radiation, respectively. Photosynthetic active radiation (PAR) reached amounts of 7.0 to 12.0 MJ.m"2 d"1, which represent about 47% of the inciding short wave radiation, almost entirely absorbed by the crowns. The cupshaped architecture provided the highest PAR transmittance level (38.2%). The least PAR transmittance levels were recorded in crowns with 4V-thinned, pyramidal, and control architectures. The ultraviolet radiation varied between 0.8 and 1.2 MJ.m"2.d_1, which correspond on an average basis to 4.9% of the inciding short wave radiation. The maximum and minimum UV transmittances were recorded in the 2V- (90.1%) and 4V-thinned crowns (4,9%), respectively. There was a good correlation between inciding short wave radiation (Rg) and radiation balance (Q*). The temperature near the fruits was always approximately 1°C greater than that of air, but in the control architecture crowns that temperature practically equaled air's, while in cup-shaped crowns the average At was 2°C higher. Trees with the 4V- and V-thinned crowns were the most productive (about 16 ton/ha), reaching 23% above the region average. All architectures tested yielded better than the control, with only 9.5 ton/ha (27% below the region average). The most productive quadrants were SW and NE. In the control was recorded the greatest natural fruit fall index (34.5%) and the cup-shaped crowns had the greatest loss due to internal collapse (87.0%). Trees with 4Vthinned and pyramidal crowns produced about 48% export fruits against 38% of the control. According to the post-harvest analyses there were increases of SSC and pH in fruits from all architectures along time storage range. Fruits from all architectures had the average TA drastically decreased until the 31s t day of storage. Type of architecture and quadrant, or their interactions, did not affect significantly SSC, TA, and pH. The most effective treatment with regard to the development of the internal and external fruit colors was the NW quadrant in V-thinned crowns.