COTTON WATER REQUIREMENTS

A field experiment with irrigated cotton was conducted at Sousa-PB, in the period from August do December, 1990. Its objective was to measur e daily maximum crop evapotranspiration (ETm) and reference potential evapotranspiration (ETo), estimated by climatological methods, in orde r to establish the seasonal behaviour of the crop coefficient (Kc = ET m/ETo). A 0.7 ha plot was planted in a 1.00 m row and 0.20 m between p lant spacing. Irrigation was made by furrows. The meteorological param eters were daily observed above the canopy. The maximum daily water co nsumption occurred in the tenth week (ETm = 6.4 mm/day) and the season al total water consumption of 440.0 mm. ETo showed a tendency for over estimating ETm in the phases of germination and vegetative growth and for underestimating it in the period of full crop development. The met hods of estimation of ETo showed statistically no significant differen ces, with Penman's method showing the lowest difference in relation to those values suggested by FAO. Kc values showed good agreement with t hose suggested by FAO. A Kc characteristic curve was established for t he crop growing season. The crop showed a low transpiration rate even in excellent soil water conditions.