It was proposed in this study to determine and analyze variations in the ratio between photosynthetically active radiation (PAR) and global solar radiation (GR) during the growth season of tomato (Lycopersicon esculentum Mill., cv. Duradoro) crop in sand substract under protected cultivation. Measurements of GR and PAR were conducted inside of a single layer polyethylene greenhouse during the dry season in Viçosa, Minas Gerais, Brazil. Simultaneously, the GR was measured in an automatic weather station. The PAR/GR ratio decreased from 1.691 to 1.574 mol MJ-1, from the first to the ninth week after transplanting, and was relatively constant, oscillating between 1.571 and 1.587 from the ninth to the thirteenth week. Thereafter, when clear sky conditions changed to cloudy days, the PAR/GR ratio increased considerably (1.93 e 2.07 mol MJ-1), reaching values near to those determined in other Brazilian locations. Based on results it is possible to affirm that little effect of leaf expansion on multiple reflections of solar radiation inside the greenhouse occurred, but a remarkable influence of the clouds in the PAR/GR ratio was verified.
greenhouse; Lycopersicon esculentum; solar radiation
