Necessidades hídricas, crescimento e desenvolvimento do algodoeiro herbáceo, cultivar BRS 201.

Abstract

A field experiment was carried out at the Experimental Field of the Brazilian Company for Agricultural Research (Embrapa - Algodão), located in the village of Barbalha - CE (07°19*S; 39°18'W; 408,07m), during the periods from August to December 2001 and 2002 in a semi-arid environment of Northeast Brazil. The main objective of the study was the determination of the water requirements of cotton crop (Gossypium hirsutum L. r. latifolium Hutch), cultivar BRS 201, under an irrigation system capable of assuring a good growth, development, and yield. The evapotranspiration was estimated and measured according with the energy balance based on Bowen ratio method and two hsimeters, respectively. The reference evapotranspiration was estimated with the Class A pan and FAO-Penman-Monteith methods, respectively. In the two field experiments a micrometeorological tower was set up inside the experimental area, for installation of two piranometer, a net radiometer, two psychrometers of copper-constantan termocouples (kept at 0.5 m and 1.5 m above the canopy of the culture) and two anemometers. Two plates for measuring soil heat flux at 0.02 m depth were also installed. These sensors were connected to a datalogger (2IX Campbell Inc) programmed to make readings at every 5 seconds and extracting averages at a 20 minutes intervals. The differences among the values of the reference daily evapotranspiration were small. However, it is recommended the use of the FAO-Penman-Monteith method because it is more accurate and used and large scale. The minimum and maximum estimated and measured Etc, during the crop season of the cotton crop were equal to 1.80 (5.80) and 2.06 (7.11), respectively, with averages of 4.46 and 5.12 mm/day. The total amounts of water consumption were equal to 450.90 mm and 517.37 mm, respectively. The maximum and the minimum daily EToFPM and EToTCA during crop season were 8.95 mm (4.37 mm) and 10.71 mm (3.73 mm) with averages of 6.42 mm and 7.12 mm, respectively. The crop coefficient Kc varied from 0.27 to 1.23, depending on the combination of the used methods. The plants of the cotton crop reached a height of 96.50 cm, a dry biomass of 123.49 g and a foliar area of 5,145.60 cm2, on the day 84 after sowing. The rates of absolute and relative growth, and liquid assimilation reached maximum values of 4.39 g/day, 0.1181 (g/g).day'\ 0.0018 g.cm"2 day, respectively. The average yield was equal to 3,014.6 Kg.ha'1.