The photosynthetically active radiation (PAR) comprises the wavelengths between 400nme 700nm, visible radiation (TAIZ and ZEGER, 2006). Presents great importance in studies on plant growth, photosynthetic rate and stomatic conductance is the radiation that excites the molecules of chlorophyll plants, starting the flow of energy through the process of photosynthesis. With the present study aimed to evaluate the performance of the model CROPGRO-Soybean in the estimation of photosynthetically active radiation (PAR) during the cycle of soybean in Cruz Alta, Rio Grande do Sul.
