Energy balance in castor bean cultivated in rainfed conditions in a mountain area in Paraiba, Brazil

Abstract

The castor bean is one of the crops that are well adapted for producing biodiesel in the northeast of Brazil, besides presenting high potentiality for producing employment and preventing rural exodus. However, despite the great economic and social importance of the castor bean, as well as water balance studies, up to now, no studies have been carried out on the energy balance for this crop. Therefore, the energy balance components in a castor bean crop growing in the mountain region of Paraiba, Brazil (“Brejo Paraibano”), were determined at a 4 ha area in the Centro de Ciências Agrárias, UFPB, belonging to the Municipality of Areia, PB (6^o 58’ S, 35^o 41’ W; 620 m). Measurements of rainfall, net and global radiation were made. Sensors at two levels above the canopy were also mounted, allowing the measurements of air temperature and relative humidity and their gradients. Below the soil surface, two different sites were provided with two thermal probes, horizontally installed at depths of 2.0 and 8.0 cm, together with a heat flux plate 5.0 cm deep for soil heat flux measurements. All data were stored in a datalogger each 30 min. The average value of the net radiation was 65% of the global solar radiation, in which 52% appeared as latent heat flux, 38% as sensible heat flux and 10% as soil heat flux. The maximum values of LE were found in the fructification phase when the castor bean are being filled up, thus indicating a major water consumption in this phase by the plant.