Advecção sobre um cultivo de amendoim irrigado.

Abstract

This Dissertation deals with the effects of advection on water loss from peanut crop in the semi-arid region of northeast Brazil. The experimental part of the study was carried out during the period September 20 to december 23, 1996 in the irrigated perimeter of the CODEVASF Experimental Station, in the city of Rodelas - Ba (lat. 08° 50'S; long. 38° 46'W; alt. 270m). Three micrometeorological towers equipped with automatic data acquisition systems were installed along the cultivated area. Incident and reflected solar radiation, net radiation, dry and wet bulb temperatures, wind speed, soil heat flux and évapotranspiration were measured throughout the study period. The micrometeorological parameters were measured each second while évapotranspiration was measured once a day and twice a week hourly data was collected during daytime. The peanut crop (Arachis hypogaea L.) was planted in an area of 2 hectares with a spacing of 0.5 m between rows. The results showed that until the phase of vegetative growth advection of humid air occurred in the first half and advection of sensible heat in second half of the field. During the flowering phase and maturation advection of sensible heat occurred in the entire field. Bare soil surface between rows was a significant source for the prodution of sensible heat. Radiation balance was affected by irrigation causing a decrease of up to 9% in hourly albedo values and up to 6% in the daily mean value. In the phase of maturation sensible heat advection caused évapotranspiration to exceed net radiation by about 50%. It is found that if the same time intervals are not considered for the measurements of net radiation and évapotranspiration totals errors of up to 2.2 MJ/m2/day may occurr and this in turn may make it difficult to detect the presence of advection.