poster - International Conference of Agricultural Engineering

3
analysis of the results were made daily, using regression analysis and considering the linear
model (y = ax + b), in which the dependent variable was the radiation balance on the studied
surface (Q * s) and the independent variable the radiation balance at the horizontal surface
(Q * H). In this analysis was considered the complete model and the one without intercept. It
was analyzed the adjustments of the regression models for the surfaces, by means of the‘t’
test, at 1% and 5%. The reference evapotranspiration accumulated on the surfaces studied
was estimated for the period of March 2011 to March 2012, obtained daily by the Penman-
Monteith method (Allen et al., 1998), corrected for each surface. The daily reference
evapotranspiration was calculated by the equation:
ETo
( PM )
0,409
900
T 273
1
0,34 V
Rn
G
Ves
e
where, ETo (PM) = reference evapotranspiration by the Penman-Monteith method, in grass, mm
d -1 ; Rn = radiation balance on each surface, MJ m -2 day -1 ; G = heat flow in the soil, MJ m -2 day -1 ;
T = average air temperature, ºC; V =average wind speed at 2 m height, m s -1 ; (e s -e) = vapor
pressure deficit, kPa; = tangent to the curve of vapor pressure, kPa ºC -1 ; = psychrometric
constant, kPa ºC -1 and 900 = conversion factor. The psychrometric constant was calculated
using the Smith equations (1990).
3. Results
Tables 1 and 2 are shown the results of the average daily radiation balance (Q *) for the
surfaces studied in the spring-summer and fall-winter periods. It was found that in the springsummer
periods the values of the radiation balance to the surfaces were similar. According to
Marin et al. (2001) the balance of radiation obtained on a vegetated surface represents the
energy available to the system to perform its physiological functions, especially
photosynthesis and perspiration, as well to processes for heating the air, the plants and the
soil. Therefore, in the fall-winter period the surface that showed the highest available energy
was 20N and the lowest 20S.
(1)
TABELA 1: Mean values of radiation balance in surfaces studied in the spring-summer
period (2002-2003).
Surface Average Q * (MJm -2 dia -1 )
H 13.1
10N 13.6
10S 13.1
20N 13.6
20S 12.7
10E 13.4
10W 13.3
20E 13.1
20W 13.0