the effects of chemical and biological fertilizers application on forage sorghum (sorghum bicolor l.) yields of different harvests

management of soil fertility via biological fertilizers inoculation is one of the most important components based on sustainable agriculture. in order to investigate the effects of biological and chemical fertilizers on yield and some morphological traits of forage yield sorghum, a field experiment was conducted as factorial based on randomized complete block design with three replications at agricultural research farm, agricultural faculty, tabriz university during growing season of 2010-2011. the first factor consisted of chemical fertilizer levels of 210 kg.ha-1 urea (100%), 150 kg.ha-1 super phosphate triple (100%), urea (100%)+ super phosphate triple (s.p.t, 100%), urea 50%+ s.p.t. 50%, and control and the second factor comprised biofertilizer levels of biosuper, phosphate barvar π, biosuper+ phosphate barvar π and control. the result showed that the sorghum could be produced three harvests during a growth season under tabriz climatic conditions. dry forage yield, leaf dry weight and stem dry weight of sorghum in the second harvest were more than other harvests, but the leaf stem ratio at the third harvest was higher than others. at the first harvest, combination of super phosphate triple (100%)+ biosuper+ phosphate barvar π, at the second harvest, the urea (100%)+ super phosphate triple (100%)+ phosphate barvar π, and at the third harvest 50% urea+ 50% super phosphate triple+ biosuper+ phosphate barvar π, increased forage yield, up to 244.6 %, 344.3 % and 121.5 % compared to the control, respectively. therefore, it was concluded that the sorghum forage yield was increased significantly with integrated application of chemical and bio fertilizers at three harvests compared to chemical and bio fertilizers usage, separately.