Micrometeorologia de um cultivo de cana-de-açúcar em Alagoas

Abstract

The main terms that apper in the physical parameterization of the surface of a sugarcane field (Saccharum o(ficinarum L. - cultivar SP70-1143), regarding the diurnal cycle as well the changes during the growth period were determined in this study. The experiment was carried out near the town of Pilar - AL (09°36' 12"S, 35°53'46"W, 107m) from December 1998 to August 1999, and included meteorological and physiological measurements. The meteorological data were collected in an automated station of the MICROMA (Micrometorology of the Atlantic Forest in Alagoas) project and the physiological data through 15 days samples. The following parameters were monitored and considered in this work: zero plane displacement (d), aerodynamic roughness length (Zo), friction velocity (u-), Bowen ratio (β), aerodynamic resistance (ra), canopy resistance (rc), leaf area index (LAI) and canopy height (ad). The observed values of d were of the order of 0.80 ± 0.02ad and those for zo, of the order of 0.085 ± 0.002ad. The friction velocity varied from 0.17 m.s-1 to 0.55 m.s-1, with an average value of 0.37±0.07 m.s-1. The daily average, using the continuous record between 08LT and 16LT, of the Bowen ratio decreased during the entire period of the study with an overall averege of 08 ± 0.3. The aerodynamic resistence also decreased along the whole period, with a maximum of 85.5 s.m-1, minimum of 17 s.m-1 and average of 37±11 s.m-1. During the experiment the culture resistance (cr) showed a overall falling trend, with average of 63±39 s.m-1 and extremes of 151s.m-1 and 26 s.m-1. The leaf area index varied from 1 to 7.8 with an average of 4.3. The growth of the canopy satisfield the well known exponential pattern, reaching the maximum of 2.6 m by day 340 after the harvest. The surface energy budget suggested the importance of the horizontal advection. During the driest period, when the average energy availability 15 ± 1.8 MJ.m-2.day-1, the latent heat flux (LE), estimated by Penman-Monteith method, was 48% of the net radiation flux (Rn) and 40% of the sensible heat flux (H). During the rainy period, the mean available energy was 10.5±2.8MJ.m-2.day-1,partioned such that 56% was for evapotranspiration (LE) and 36% for warming the air (H). The soil heat flux was only 11% of Rn (1.7±0.4MJ.m-2.day-1) during the period and 5.5% during the rainy period (0.6±0.2MJ.m-2.day-1).