Avaliação da evapotranspiração e desenvolvimento da cultura do milho irrigado na região de Rio Largo – AL

Abstract

A agrometeorological experiment was conducted in the Sciences Agrarians Center of the Federal University of Alagoas, Rio Largo - AL (09 28' S, 35 49' W and 127 m altitude), in the period of January to April 2002, to evaluate methods of the reference evapotranspiration (ET o), energy balance and crop evapotranspiration (ETe) of irrigated corn. Automatic system of daters acquisition Micrologger-21XL of Campbell Scientific was utilized to measure meteorological variables. The ETo was evaluated by the methods: Penrnan-Monteith (PM), Linacre (Lin), class "A" (C.A), Blaney-Cridlly (B.C), Penman 1948 (Pen) and radiation of FAO (Rad). The daily médium ETo of the models varied of 2.02 mm to 5.42 mm with average of 3.99 mm. The PM pattern was consisered for comparation of the methods. The concordance analysis done with Bse in the Willmontt coefficient “d” showed that Rad followed by Pen there have the resulted more similar to the patern and the C.A it was fewer agreed. The corn crop, variety BR 106 reached a height of 2,72m and a leaf área índex (LAI) maximum of 4,51. The yield was around 5,0 t há-1. The aerodynamic resistance was calculated in function of the crop aerodynamic parameter (ra1) and function of the Wind velocity (ra2). At Ra! In the first 25 days after plantation it varied of 80 to 151 s m-1, in the remaining of the crop cycle, it decreased to the range of 35 to 71 s m-1 and ra2 it was more elevate in all cultivation cycle, but it presented a smaller variation of 117 to 175 sm-1. The variation on crop resistence with base in the radiation net (Rn) and LAI was of 26.487,3 to 38,5 s m-1 and with bae only on the LAI it was of 20.000,00 to 44,34 s m-1. The Rn, over the crop, and soil heat flux (G) was measured. The daily average of the Rn was 13,58 MJ m-2 and G 0,42% of the Rn (daytimes daters). The energy balance (BE) for Bwoen ratio, with the surface temperature (canopy temperature, obted for pegeometric measure) anda ir temperature 2,0 m above the maize canopy, alongo f the crop cycle, it indicated that on the average 84,36% of the available energy wre used for latent heat flux (λE) and 15,21% as sensible heat flux (H). In the BE method, in function of the ra1, the repartition of the Rn was 50,62% for λE and 48,94% for H, and in the BE based on ra2 78,51% was for λE and 21,07% was for H. The crop evapotranspiration (ETc) was determined for Bowen ratio (RB), Penman-Monteith model (PMc) and BE. The ETc average change of 1,18 mm to 6,37 mm, with average of 4,15 mm day-1. The RB was considerated standard and the results obted for BE it agreed in 100% with the pattern. The crop coefficient (Kc) mean was 0,58 n the initial phase, 1,23 on silking and 1,07 in the end crop.