Medidas e estimativas dos componentes do balanco de radiação sobre um cultivo de algodoeiro herbáceo irrigado.

Abstract

This research employed data from a field experiment conducted in the LAJAT/DNOCS Experimental Station, in the irrigation settlement of São Gonçalo, Sousa-Pb. Its objective was to study the behaviour of cotton (Gossypium hirsutum r. latifolium, cultivar CNPA early 1) crop, grown under irrigated conditions in a 8.000m plot planted in a 1.00m row spacing and with 0.20m between plants. The measured components of the radiation balance were compared to those obtained from conventional empirical formulae, with the purpose of adjusting the estimation equations to the local conditions. The global solar radiation (rS)Í reflected solar radiation (RÍ;) and net radiation (%j) were continuosly registered and measured instantaneouly at 30 minute intervals. Hourly measurements of dry and wet bulb temperatures, canopy temperature and maximum and minimum daily temperatures were also obtained. The canopy height (h) and leaf area index (LAI) were measured at three days interval. The canopy reflectance varied from 0.14 at the beginning of the growing season to 0.25 at the end of the growning phase and then decreased to 0.21 at the end of the crop cicle. The best estimate of the atmospheric radiation (RT)• was obtained from those equations which take into account simultaneouly air temperature and water vapor pressure in the air. Penman's equation presented the best results for predicting net radiation, especially when adjusted tp the local conditions.