Índices Morfofisiológicos e Uso de Radiação Solar por um Cultivo de Cana-de-Açúcar Irrigada no Semiárido Brasileiro (Morphophysiological Indices and Radiation Use by an Irrigated Sugarcane Crop in the Brazilian Semi-Arid)

Os indices morfofisiologicos e parâmetros de eficiencia do uso de radiacao foram determinados para a cana-de-acucar irrigada, RB92579. O experimento foi conduzido no municipio de Juazeiro-BA, Semiarido brasileiro. Foram obtidas medicoes de biomassa seca acumulada pelas folhas, colmos e total da parte aerea, e do indice de area foliar. Adicionalmente, dados de radiacao solar global e de radiacao fotossinteticamente ativa foram medidos acima e abaixo do dossel da cultura. Por meio desses dados foram calculados os indices morfofisiologicos, a fracao da radiacao fotossinteticamente ativa (fRFA), o coeficiente de extincao (ke), o uso eficiente de radiacao (UER) e a eficiencia fotossintetica (EFT). A taxa de crescimento absoluto aumentou substancialmente ate atingir o valor maximo de 41,8 g m-2 d-1 aos 200 dias apos o corte (DAC). O valor maximo de fRFA foi em torno de 99%, permanecendo constante dos 213 DAC ate o final do ciclo. A magnitude do parâmetro ke foi 0,72. Baseado nas medicoes do BSTPA verificou-se que os valores aproximados de EFT e UER foram 2,67 g MJ-1 e 1,29 g MJ-1, respectivamente. Os resultados mostraram que a cana-de-acucar irrigada no Semiarido brasileiro possui padroes de crescimento superiores aos de outros ambientes de cultivo registrados na literatura. A B S T R A C T The morphphysiological indices and parameters of radiation use efficiency were determined for irrigated sugarcane, RB92579 cultivar. The experiment was carried out in the district of Juazeiro, State of the Bahia, located in the Brazilian semi-arid. Measurements of dry biomass accumulated by leaves, stalk and total shoot, and leaf area index (LAI) were carried out. Additionally, global solar radiation and photosynthetic active radiation were measured above and below the crop canopy. Using these data, morphphysiological indices, the photosynthetic active radiation fraction (f PAR ), the extinction coefficient (ke), the radiation efficient use (REU) and the photosynthetic efficiency (PTE) were calculated. The absolute growth rate tended to increase substantially until reaching the maximum value of 41.8 g m -2 d -1 , which was observed 200 days after cutting (DAC). The maximum value of the f PAR was around 99%, remaining constant from 213 DAC until the end of the crop cycle. The magnitude of the ke parameter was 0.72. Based on measurements of DBTS, it was verified that the approximate values of the PTE and REU were 2.67 g MJ -1 and 1.29 g MJ -1 , respectively. Results showed that the irrigated sugarcane has excellent growth patterns when cultivated under semi-arid conditions when compared to others environments cited in literature. Keywords: growth, extinction coefficient, radiation use efficiency.