http://lattes.cnpq.br/6235891408425870; RODRIGUES, Marcos Fernando Guedes.
Résumé:
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.
