Malhas fotosseletivas na produção de cana-de-açúcar

Abstract

Brazil is the world's largest producer of sugarcane and stands out in the world for the production of ethanol. The propagation is of the vegetative type, and the use of the technique of production of pre-sprouted seedlings has raised the sanity and quality of the material for propagation. The objective was to characterize photoselective shading screens regarding the variation of the micrometeorological elements, with emphasis on the production of seedlings and the reflexes in the field production. The first stage of the research was carried out in a protected environment at the UFRPE, (Recife-PE), the second stage under field conditions at the Carpina-PE experimental station. The seedlings of cultivar RB92579 were obtained by the technique of production of pre-sprouted seedlings. The protected environments were divided in four modules covered with: PEBD antiUV + red ultranet screen Solpack® with 35% shading, PEBD antiUV + white screen Solpack® 50% shading, PEBD antiUV + freshnet screen Solpack® 50% shading e PEBD antiUV without shading screen. Micrometeorological data were recorded in the internal modules and in the external environment, the solar radiation spectrum in each module and the biometric and physiological variables of the plants. The experimental design was completely randomized, and in step 2, the experiment was installed in the field in a randomized block design. In the two stages, the multivariate analysis of main components was used based on the correlation matrix among all the variables to analyze the association between the cultivation modules, the micrometeorological, biometric and physiological variables of the crop. The air temperature of the protected environment was 8% higher in relation to the external environment. In the module with PEBD antiUV + freshnet, transmittance of 24.3% of global solar radiation, 37% of photosynthetically active radiation and 27% of solar radiation of the red spectrum (625-700 nm) was observed. PEBD antiUV + white e PEBD antiUV + red ultranet transmitted 18% of the solar radiation in the blue spectrum (440-485 nm). In the modules with PEBD antiUV + red ultranet e PEBD antiUV + white there was a greater ratio of the blue/red light spectrum. The PEBD antiUV + white module provided 78.9% seedling sprouting. After the sprouting period, substrate temperature above 30.2 °C caused higher seedling mortality. From 13 to 27 days after planting the use of shading screen in the cultivation modules induced the greatest growth and development of seedlings. The module with PEBD + freshnet promoted lower mortality of seedlings in protected environment, higher chlorophyll content and higher quality seedlings. At 305 days after transplanting, the plants from the PEBD antiUV + freshnet e PEBD antiUV + red ultranet showed higher accumulation of carbohydrates, sucrose and production of 130 and 145 t ha-1, respectively. Therefore, the module with PEBD antiUV + white favored seedling sprouting and the module PEBD antiUV + freshnet provided higher quality and lower mortality of seedlings. Seedlings from environments covered with PEBD antiUV + red ultranet e PEBD antiUV + freshnet presented higher agronomic attributes at the end of field cultivation.