Effect of planting date and plant density on net photosynthesis, stomatal conductance, leaf chlorophyll index and grain yield of soybean in Meghan and Karaj areas

In order to study the effects of canopy temperature during reproductive growth stages on physiological characteristics and Soybean grain yield through different planting dates and plant densities, an experiment was conducted as split factorial based on Randomized Complete Block Design with three replications in Karaj and Moghan areas in 2011-2012. The factors included three planting dates, May 5th, June 5th and July 5th, three plant densities, 300, 400 and 500 thousand p/ha and two cultivars, Williams and L17. Results showed that the net photosynthesis in Karaj (16.14 µmol Co2 m-2s-1) was lower than Moghan area (19.13 µmol Co2 m-2s-1). The maximum stomatal conductance (330.6 mmol m-2 s-1) and net photosynthesis (19.13 µmol Co2 m-2s-1) were related to planting date at June 5th. The highest stomatal conductance (325 mmol m-2 s-1) was observed in 400000 p/ha. The leaf chlorophyll index at 300 and 400 thousand p/ha in Moghan region was more than Karaj. The second planting date and second plant density had the maximum rate of grain yield (3142 and 3154 kg/ha respectively). Except chlorophyll index, there was no significant difference in other traits between cultivars and the highest chlorophyll index was related to Williams cv. in Karaj area. According to the results and in order to prevention of encountering the pod set and grain filling stages with high canopy temperature, it is better that soybean planted in mid of June with 400000 p/ha.