M. S. B. de Moura

Demanda hídrica e eficiência do uso de água da cana-de-açúcar irrigada no semiárido brasileiro

The objective of this work was to accomplish an analysis of the water use efficiency in a production system of irrigated sugarcane located in the Lower-Middle Sao Francisco river basin, Brazil. Indicators based on the crop yield and the water application performance in the production system were used. These indicators were calculated through accumulated dry biomass, industrial yield data and through the values of reference evapotranspiration, crop evapotranspiration and the water volume that entered in the system by rain and irrigation (P+I). It was verified that, the highest water use efficiency of crop occured between 7th and 8th month, due to increase in the stalk biomass partition and radiation supply, and due to reduction of ETc in response tumbling of the plants. The used indicators demonstrated that the water demand of crop was adequately in relation to maximum evapotranspiration of crop. The irrigated sugarcane presented a production efficiency of 9.49 kg of stalks, 1.22 kg of sugar and 875.23 mL of alcohol per m3 of ETc and of 5.36 kg of stalks, 0.69 kg of sugar and 494.14 mL of alcohol per m3 of P+I.

Estimating black globe temperature based on meteorological data.

An automatic weather station, comprising of temperature and humidity sensors, a pyranometer, an anemometer, and a thermocouple inside a black globe, was installed in a grassed area at the University of the State of Bahia - UNEB, Juazeiro County, Bahia State, Brazil. Half of the data collected at this station was used to generate models (simple or multiplicative) for estimating the Black Globe Temperature (BGT). Model performance was evaluated by using the second half of the data. Statistical precision and accuracy indices and statistical errors were used to analyze the collected data and the Student`s t test was used to evaluate the significance of the model parameters. Two models to estimate the BGT using meteorological variables were obtained: BGTd = [1.360 Tair d - 2.358]·[0.075 ln(Rs) - 0.562] and BGTn = [0.942 Tair n]. One model was elaborated for daytime BGTd), when the air temperature (Tair d) and solar radiation (Rs) were combined to generate a multiplicative model (R2 = 0.877), and a second model was developed to determine the BGT values for night-time (BGTn) based on the night-time air temperature (Tair n) (R2 = 0.962). The models developed resulted in great performance to predict the black globe temperature, allowing the estimation of bioclimatic indices to assess the conditions of the environment, to accomplish regional studies, and to indicate best house designs for animals.

Acúmulo e exportação de macronutrientes pela cana de açúcar irrigada no Semiárido brasileiro.

A marcha de absorcao de nutrientes, estabelecida por uma curva de acumulo de nutrientes na planta ao longo de seu ciclo, indica a fase de desenvolvimento da cultura que apresenta maior exigencia de um determinado nutriente. Objetivou-se determinar o acumulo e exportacao de macronutrientes pela cana-de-acucar, variedade RB92579, cultivada remcondicoes tropicais semiaridas na Usina Agrovale, em Juazeiro-BA, regiao do Submedio do Vale do Sao Francisco. O experimento foi conduzido em um Vertissolo Hidromorfico. Foram demarcadas 03 subareas nas quais se coletou amostras de material vegetal separadas em folhas verdes, bainhas, folhas e bainhas mortas, pseudocolmo, colmo e a parte imatura, em dez epocas ao longo do ciclo (66, 87, 112, 133, 168, 220, 242, 280, 352 e 385 dias apos o corte - DAC). As amostras foram levadas a estufa a 65 o C ate peso constante para obtencao da biomassa seca, na qual foram determinados os teores de N, P, K, Ca, Mg e S. A maxima absorcao dos nutrientes pela cultura da cana-de-acucar ocorreu no periodo compreendido entre 220 a 352 DAC. O acumulo de nutrientes obedeceu a seguinte ordem decrescente: K > N > Ca > S > P > Mg. A colheita e responsavel pela maior exportacao de nutrientes acumulados pela cultura da cana-de-acucar, cerca de 60 a 90 % do total de nutrientes acumulados sao exportados pela colheita. Durante o ciclo de cana-soca, foram utilizados pela variedade 2,50; 0,33; 5,35; 0,86; 0,19; 0,55 kg de N, P, K, Ca, Mg e S, respectivamente, para cada tonelada de colmo produzida.