Balanço de radiação e consumo hídrico de um cultivo de feijão macassar (Vigna ungniculata L. Walp) irrigado).

Abstract

This work resulted from the analysis of the data of an agrometeorological experiment carried out in the irrigated perimeter of the DNOCS, in the municipality of Sumé-Pb. The objective of this study was to evaluate the components of the energy and radiation balance in the main phases of the development of irrigated macassar bean (Vigna Ungniculata, L. (Walp)), as well as to study the water needs of the crop in the semi-arid conditions of the Paraíba . The experiment was conducted from October 1988 to January 1989. The components of the radiation balance were monitored through hourly readings and daily records of the radiation balance (Rn); incident global solar radiation (Rs); and reflected (Rs). The other atmospheric parameters were measured, with instruments installed on the crop. The maximum evapotranspiration of the crop (ETm) was measured in two constant water table evapotranspyrometers installed in the experimental area and the reference evapotranspiration (ETo) was estimated by the methods of PENMAN; DOORENBOS & PRUITT; PRIESTLEY & TAYLOR; JURY & TANNER; "Class A" TANK; LINACRE and HARGREAVES. Daily values ​​of ETm and ETo were used to calculate the crop coefficient (Kc = ETm / ETo). The vegetation reflectance (Pv) presented a diurnal variation, with minimum values ​​around midday and maximum values ​​at sunrise and sunset. From the seasonal point of view, Pv presented daily fluctuations due to soil moisture status, but in general, it varied from 0.10 soon after germination to 0.21 at the end of the flowering phase. The best estimate of Rn was obtained by the equation of PENMAN (1948) adapted to the local conditions and culture, with standard error of estimation of Exy = 22.38 cal / cm2. 12hs. The balance of radiant energy available accounted for 70.41% of the radiation s the global home incident during the growing season. All ETo estimation methods employed showed a tendency to overestimate the vegetative growth and flowering stage, and to underestimate the evapotranspiration measured in the maturation phase of the crop. A curve representing the seasonal variation of Kc was established for the macassar bean at the local conditions of the experiment. The analysis of variance showed that there is no significant difference between the Kc values ​​suggested by the FAO and estimated by the different methods at a significance level of 1%. The water consumption of the crop along the phenological phases is 478.1mm. During the phase of complete development of the culture, the average daily water consumption was 7.6 mm / day.