Seeding rate effects on forge productivity and nutritive value of sorghum

In Ethiopia, the use of traditional and improved grain sorghum [Sorghum bicolor (L.) Moench] variety as green forage crop is limited mainly by the large stalk thickness and low nutritive values. An experiment was conducted to explore if forage biomass accumulation and nutritive values could be managed by seeding rates. Two improved dual-purpose grain sorghum varieties (Melkam and Chelenko), and one traditional local variety (Masugi) each representing early and late maturity groups were sown for 2 yr at three locations in randomized complete block design (RCBD) with three replications involving five seeding rates (12.5, 25, 50, 75, and 100 kg ha(-1)). The results showed significant effects of year, location, variety, seeding rate, and the interactions on different variables. These main effects contributed more and the interactions less to the total variation observed on different variables. Increasing the seeding rate significantly decreased stalk thickness, neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL), but significantly increased in-vitro organic matter digestibility (IVOMD) concentration by up to 6.6% with no significant effect on forage dry matter accumulation. Among the varieties significantly more dry matter accumulation was observed for the late-maturing varieties, whereas the early-maturing variety showed significantly greater crude protein (CP) and IVOMD with significantly less NDF, ADF, and ADL concentrations across the different locations. Thus, increasing the seeding rate above the recommended 12.5 kg ha(-1) for grain could help improve forage potential of dual-purpose grain sorghum varieties in Ethiopia.