Coeficiente de cultura para nogueira-pecã na região de Cachoeira do Sul, RS

Abstract

The production of pecans has gained prominence in Brazil, especially in the state of Rio Grande do Sul. However, droughts in the central region of the state have put the production at risk. Irrigation becomes essential, and for its correct management, the knowledge of crop evapotranspiration (ETc), which is obtained from the reference evapotranspiration (ETo) and the crop coefficient (Kc). Kc is considered a complex measurement and for pecan crop, there is no study in Brazil. The objective of this work was to evaluate the pecan’s Kc in the region of Cachoeira do Sul - RS obtained with remote sensing using the geeSEBAL application. An adult pecan orchard, the spatial distribution of ETc was obtained in geeSEBAL from 1992 to 1999, from September to May. The representative ETc values of the days of the images were later processed in the QGIS software. Kc was calculated from ETo what was calculated using the standard Penman-Monteith method for the same days. The comparasion values of Kc were obtained with the values proposed by Allen et al. (1998) using the RMSE (root mean squared error). The highest RMSE value (1.03) was obtained for the intermediate period (september to december), what demonstrates greater distance from the Kc values compared. Despite the Kc curvature presenting low values throughout the cycle (with means of 0.56, 0.90 and 0.77), the period of development was configured as the one with the highest water demand, with an average Kc of 1.14, in contrast to other works in the literature. The humid climate and adequate water supplementation may explain the curvature behavior, which, even so, remained within what had been reported in others regions of the world. The geeSEBAL shows to be a useful tool to estimate the crop values of adult pecan nut in the Cacheoira do Sul – RS region, thereat, it could auxiliate in the irrigation management.