Effect of Density on Connotative and Collective Yield of Forage Sorghum Under Water Limitation

This experiment was conducted to evaluate the effect of limited irrigation and sowing density on two forage sorghum varieties. The experiment was conducted in Research Farm of College of Agriculture، University of Tehran during 2007 growing season. The experiment was conducted according to split plot factorial in a randomized complete block design with three replications. The main factor consisting of irrigation after 70 (control)، 100 (medium water stress) and 130 (severe water stress) mm accumulative evaporation from evaporation pan class A and the sowing density of 15، 20 and 25 plants per square meter and two sorghum varieties (Speedfeed and Pegah) were allocated as factorial arrangement to the subplots. The results indicated that the highest and lowest dry matter digestibility (IVDMD) in control conditions (IR70) was related to Pegah with density of 25 plants per square and Speedfeed with density of 15 plants per square meter، respectively. In drought conditions، Pegah have the higher amount of crude protein (CP). With increasing of density، the percent of crude protein was reduced in medium water stress and severe water stress levels. With increasing stress levels of water soluble carbohydrates (WSC) increased in both cultivars (Speedfeed and Pegah). The acid detergent fiber (ADF) was reduced with increasing plant density in Speedfeed cultivar in control conditions (IR70) and moderate levels of stress (IR100). The highest forage yield was produced by Speedfeed variety at the control، medium water stress and severe water stress treatments with 25 plants per square meter density. The lowest forage yield was observed at density of 15 plants per square meter in severe water stress and Pegah cultivar.