Evapotranspiração e coeficiente de cultivo da cana-de-açúcar cultivada nos tabuleiros costeiros do Estado da Paraíba.

Abstract

The cultivation of sugar cane has great expression in the country, and for the state of Paraiba, represents the main crop in the Coastal Plains. The productivity of sugar cane can be increased with the rational use of supplementary irrigation, which can be more easily determined when we know the values of evapotranspiration (ETo, mmd-1) and the crop coefficient (Kc) along the crop cycle, used in determining the evapotranspiration of the culture (ETc, mmd-1), corresponding to the depth of irrigation to be applied. The method of energy balance based on the ratio of Bowen provides the indirect determination of ETc. This research project used data from field experiment conducted from November 2011 to September 2012, in an area of commercial cultivation of sugar cane, irrigated by a center pivot, aiming to determine the daily values and the behavior of ETc and Kc along the cultivation cyle of sugar cane grown in the Coastal Plains of the state of Paraiba. Over the period of observations, the total precipitation was 873.6 mm, the daily average temperature ranged from 21.2 to 28.4 °C. The albedo average was 18.6 %. 60.6% of the data were consistent, enabling the performance of balance sheets of radiation and energy. Of the 279 days observed, 99.28% were considered partially cloudy and 0.72% considered under overcast conditions. It was verified that 60.6% of the collected data presented physical consistence to be used for estimating the sensible heat and latent heat. On average, 87.2% of the net radiation was used as latent heat, 10% as sensible heat and 1.8% as heat flux from the soil. The evapotranspiration of reference accumulated 1,538.3 mm, ranging from 1.1 to 8.2 mmd-1. The accumulated evapotranspiration of the culture was 1,008.4 mm, with an average of 2.6 mmd-1 in phase I and of 3.9 mmd-1 in phase III, and the crop coefficient of 0.429 and 0.767, respectively.