Necessidade hídrica e coeficiente de cultivo de variedades de plantas forrageiras no semiárido do Brasil.

Abstract

For a better agricultural performance in the Northeast of Brazil, an adequate management of irrigation water is necessary. This has stimulated the cultivation of crops with high water use efficiency, for example, the fodder palm, which although it is adapted to regions of semi-arid climate, presents changes in production according to water availability. The objective of this study was to determine the water requirement, the thermal demand and the coefficient of cultivation of fodder palm varieties in the semi-arid region of Brazil. Three varieties of fodder palm were used (elephant ear Opuntia fícus-indica L.; baiana and chick Nopalea cochenillifera Salm) in a field experiment in Santa Luzia-PB, fertirrigated with 150 kg ha-1 of N. The soil water balance was performed to determine the actual crop evapotranspiration (ETr) under hydric restriction. For the determination of crop evapotranspiration (ETc) and thermal requirement, three lysimeters of drainage located in the center of the experimental area were used. Each lysimeters contained four plants with similar characteristics and under the same management system of the external plants. A fourth lysimeters was planted to determine reference evapotranspiration (ET0). Based on the emission of cladodes and the sum of degrees days, four phenophases were determined for the forage palm. The mean reference evapotranspiration values determined by Penman-Monteith (ET0PM) and by lysimetry (gram) (ET0G) were 6,2 and 7,2 mm d-¹ respectively. The daily mean values of actual crop evapotranspiration (ETr) and crop coefficient (Kc) under water restriction were: 1,4 mm d-1 and 0,31; 0,27; 0,27 for the elephant ear varieties; baiana and chick respectively. The daily average values of crop evapotranspiration and crop coefficient determined by means of lysimeters of drainage were: 4,8; 4,8 and 4,6 mm day-1 and 0,72; 0,70 and 0,70 for the elephant ear, baiana and chick varieties respectively. The basal temperature of the palm was equal to 18 °C for the three varieties and the accumulated thermal sum in the period was over 4000 °C.