Adjustment of the photothermic model to estimate soybean development and leaf area index

The present study was carried out to adjust the soy population development model and the leaf area index model for the IAS 5 cultivar. Different sowing dates were used in two experiments as source of development variation during 2004/2005 (three dates) and 2005/2006 (four dates) in the IRDeR (Instituto Regional de Desenvolvimento Rural) located in Augusto Pestana, in the State of Rio Grande do Sul (28 degrees 27' 17 " S and 53 degrees 54' 50 " W). The main crop development phases were identified according to the Feher & Caviness phenological scale, and the leaf area index was determined in four occasions: at the final period of plant population installation (V6); at the beginning of flowering (R1); at the beginning of seed filling (R5), and at the beginning of maturation (R7). The minimum and maximum temperatures were obtained daily. After the adjustment of the genetic coefficients, the model was formatted using the program Stella 5.0. The soy development model presented a suitable performance, precise estimates from the original data. The leaf area index model also presented satisfactory estimation.