Coeficiente de cultivo do feijão-caupi no Vale do Gurguéia – Piauí.

Abstract

The determination of the values of the crop coefficient (Kc) is basic to obtain the crop water demand along its development stage. The present work determined the Kc values of the cowpea (Vigna unguiculata (L.) Walp.) in diverse stages of its development aiming the rational managment of irrigation. The experiment was carried out in Gurguéia - Piauí (8°26'S, 43°47'W and 281m), microregion of the Valley of the Gurgueia River. The crop evapotranspiration (ETc) was determined by weighing lysimeters. The meteorological data were obtained from an automatic weather station and used to estimate the reference evapotranspiration (ETo) by Penman – Monteith method. The crop coefficients started from 0.65 to 1.20 by 55 days after plantation.