Crescimento de variedades RB de cana-de-açúcar irrigadas e fotossíntese modelada pela radiação solar.

Abstract

Growth models for the sugarcane crop express plant growth based on the net photosynthesis (gross photosynthesis less respiration). Determination of gross photosynthesis (GP) can be made according to the intercepted solar radiation by a rectangular hyperbolic equation. Therefore, this work, conducted at the Center for Agrarian Sciences, Federal University of Alagoas, aimed to evaluate RB varieties (RB92579, RB863129, RB931003, RB93509, RB72454, RB867515, RB951541, RB971755 and RB98710) of irrigated sugarcane in relation to the intercepted photosynthetic active radiation (PARINT) and the estimation of accumulated GP from February 2008 to February 2009. To achieve this, biometric measurements (leaf area and number of tillers) and production variables: tons of cane per hectare (TCH) and tons of sugar per hectare (TSH) were performed in a randomized outline with four repetitions. The photosynthetic irradiance (PAR) was estimated as 44% of the solar irradiation (Rg), and PARINT as the difference between PAR and transmitted PAR (PART). The PART was determined using the Beer law ( ( K IAF) T RFA = RFA exp − ), with the coefficient of light attenuation (K) equal to 0.58. The estimation of daily GP was obtained by a numerical integration with trapezoidal approach. It was also made a temporal analysis of growth through simulations of leaf area index (LAI) according to degree-days (GD). The start of the cultivation (365 days duration) was considered the 1st day of each month for the four years (2004-2007). The TCH and TSH had correlations with the accumulated PARINT and GP during the cycle. The average solar radiation of the region's rainy season, from May to August, (71 to 193 days after ratooning) was 14.9 MJ m-2.. The RB92579 variety had the highest values TCH and TSH as the highest estimates of accumulative PARINT and GP during the cycle. In simulations of growth for the RB varieties of sugarcane, the months of March and February had the highest accumulation PARINT and GP.