ABSTRACT The objective, in this research, was to evaluate the agricultural productivity and the financial performance of levels of irrigation in the cassava. For this, experiment was carried out, under a randomized block design, with six irrigation levels, as a function of crop evapotranspiration (L0 = 0% (rainfed), L1 = 40%, L2 = 80%, L3 = 120%, L4 = 160% and L5 = 200% of ETC) and four repetitions. Was evaluated: length and mass of roots, productivity of maximum physical and economic efficiency of roots and productivity of the aerial part. The irrigation level L5 or total useful water of 1,023 mm, got greatest productivity of the aerial part, 57 Mg ha-1. With a total useful water of 926 mm, this irrigation level, generated the greatest length and mass of roots per plant and the maximum physical productivity, 94 Mg ha-1. As well as the root yield of maximum economic efficiency, which is achieved with a total usable water, 914 mm. Among the irrigation levels studied, L3 (963 mm) is the one that provides the greatest productivity of roots, 90 Mg ha-1, and gross revenue 167% higher than in areas cultivated under rainfed conditions. Therefore, irrigation of cassava is economically viable.

ABSTRACT The aim of this research was to evaluate the physiological and productive aspects of irrigated cassava crop. The statistical design used was randomised blocks, with six treatments and four replications. The used treatments were irrigation levels, based on the crop evapotranspiration – ETC – (L0 = 0% [rainfed], L1 = 40%, L2 = 80%, L3 = 120%, L4 = 160% and L5 = 200% of the ETC) and the analysed physiological variables were: gas exchange, the quantum efficiency of photosystem II (PSII) and the soil plant analysis development (SPAD) index. The growth and crop productivity were also evaluated through of the leaf area index (LAI), the number and productivity of commercial roots and total biomass. In this research, the total irrigation depth was defined as the irrigation depth plus the effective rainfall. The estimated ETC was 1,030 mm over the 12-month production cycle and the greatest value for LAI and SPAD were 7.6 and 57.4, respectively, obtained in irrigated areas with the level of 80% of the ETC. While, in the areas irrigated with 120% of the ETC, were obtained the highest values of root productivity (93 Mg·ha–1), total biomass yield (149 Mg·ha–1) and photosynthetic rate (22.4 μmol CO2·m–2·s–1). On the other hand, with irrigation equivalent at 200% of the ETC were obtained the greatest values of internal CO2 concentration (245 μmol CO2·m–2·s–1), stomatal conductance (0.35 μmol H2O·m–2·s–1) and effective quantum efficiency (0.68).

RESUMO: A determinação da evapotranspiração real da cultura (ETa) é importante para o manejo da irrigação. Os principais métodos e modelos físicos de estimativa da ETa requerem dados que não são facilmente disponíveis. Neste trabalho, obteve-se o coeficiente da cultura (Kc) da laranja lima na fase inicial de desenvolvimento e avaliou-se o desempenho do modelo semi-empírico de Poulovassilis acoplado a um balanço hídrico simplificado na estimativa da ETa. A ETa (medida) foi obtida a partir da variação temporal do conteúdo de água no solo, obtida através da reflectometria no domínio do tempo (TDR). O modelo de POULOVASSILIS et al. (2001) assume que a redução da evapotranspiração da cultura é expressa por uma função exponencial do armazenamento de água do solo e por um coeficiente de ajuste empírico (ca). O armazenamento de água do solo foi obtido através do balanço hídrico (BH), diário e decendial, contabilizando as entradas e saídas de água do sistema. O parâmetro empírico ca foi obtido por modelagem inversa. O valor ótimo de ca obtido por modelagem inversa 0,05 para o BH diário e 0,03 para o BH decendial. O modelo apresentou melhor desempenho para o BH diário, comparável a outros modelos de estimativa da ETa. O Kc médio para fase inicial da laranja lima foi igual a 0,85.

ABSTRACT: Determining actual crop evapotranspiration (ETa) is paramount for irrigation management. The principal measurement methods and physical models generally require crop and weather data that are not readily available. We determined the crop coefficient (Kc) of sweet oranges during the initial development stage and evaluated the performance of the Poulovassilis semi-empirical model coupled with a simple soil water balance for estimating the ETa. The ETa was inferred from the variation in the soil water content over time, measured by time-domain reflectometry. In the Poulovassilis model, the ETa is obtained by multiplying the crop evapotranspiration (ETc) by an adjustment coefficient (ca), which accounts for a reduction in the evapotranspiration caused by soil water depletion. Soil water storage was obtained using the daily and 10-day soil water balances, computed by considering inputs and outputs of water from the system. The empirical parameter, ca, was determined using inverse modeling. The optimal ca value obtained through inverse modeling was 0.05 and 0.03 for the daily and 10-day soil water balances, respectively. The model performed better for the daily soil water balance than the 10-day balance, with performance comparable with the other ETa models. Average Kc during the sweet orange initial crop stage was 0.85.

RESUMO O objetivo do presente trabalho foi estabelecer o modelo digital de elevação e sua resolução horizontal para interpolar a temperatura do ar anual para o estado de Alagoas via modelos de regressão linear múltipla. Ajustou-se um modelo de regressão linear múltipla a séries (11 a 34 anos) de temperatura do ar anual de 28 estações meteorológicas dos estados de Alagoas, Bahia, Pernambuco e Sergipe, em função da latitude, longitude e altitude. Os modelos de elevação considerados nas análises foram o SRTM e o GTOPO30, com resoluções originais de 90 e 900 m, respectivamente. O SRTM foi reamostrado para as resoluções de 125, 250, 500, 750 e 900 m. Na espacialização da temperatura do ar para Alagoas, utilizou-se da regressão linear múltipla aplicada a cada modelo de elevação e resolução espacial e a um grid com a latitude e longitude. Para Alagoas, as estimativas baseadas no SRTM mostraram erro padrão de estimativa (0,57 ºC) e dispersão (r2 = 0,62) inferiores às obtidas pelo GTOPO30 (0,93 ºC e 0,20). No caso das resoluções do SRTM, não se observaram diferenças significativas entre o erro padrão (0,55 ºC; 750 m-0,58 ºC; 250m) e a dispersão (entre 0,60 - 500 m e 0,65 - 750 m) das estimativas. A espacialização da temperatura do ar anual para Alagoas via modelos de regressão múltipla aplicados ao SRTM mostra concordância superior à obtida com o GTOPO30, independente da resolução espacial.

ABSTRACT The aim of this study was to establish a digital elevation model and its horizontal resolution to interpolate the annual air temperature for the Alagoas State by means of multiple linear regression models. A multiple linear regression model was adjusted to series (11 to 34 years) of annual air temperatures obtained from 28 weather stations in the states of Alagoas, Bahia, Pernambuco and Sergipe, in the Northeast of Brazil, in function of latitude, longitude and altitude. The elevation models SRTM and GTOPO30 were used in the analysis, with original resolutions of 90 and 900 m, respectively. The SRTM was resampled for horizontal resolutions of 125, 250, 500, 750 and 900 m. For spatializing the annual mean air temperature for the state of Alagoas, a multiple linear regression model was used for each elevation and spatial resolution on a grid of the latitude and longitude. In Alagoas, estimates based on SRTM data resulted in a standard error of estimate (0.57 º C) and dispersion (r2 = 0.62) lower than those obtained from GTOPO30 (0.93ºC and 0.20). In terms of SRTM resolutions, no significant differences were observed between the standard error (0.55 °C; 750 m - 0.58 ºC; 250m) and dispersion (0.60; 500 m - 0.65; 750 m) estimates. The spatialization of annual air temperature in Alagoas, via multiple regression models applied to SRTM data showed higher concordance than that obtained with the GTOPO30, independent of the spatial resolution.