Effect of row spacing and sowing density on sorghum forage yield and quality

Sorghum dry matter yield (DMY) and forage quality were evaluated at two row spacings (75 and 20 cm) and two sowing densities (33 and 65 seeds m(-2)), with harvest at a 300 g kg(-1) whole plant dry matter concentration. Trials covered three consecutive growing seasons (2007, 2008 and 2009) with progressively lower annual rainfall. The year x row spacing interaction had no effect on traits, except for plant height. Year did affect the traits, except for whole plant dry matter concentration (322 g kg(-1)) and protein content (97.6 g kg(-1)). Annual DMY ranged from 10 t (2007) to 17 t ha(-1) (2009), and 10 t (75 cm row spacing) to 16.6 t ha(-1) (20 cm). In 2007, panicle dry weight was 109.4 g kg(-1) higher than in 2008 and 158.1 g kg(-1) higher compared to 2009. Thousand-grain weight was 13.66 g kg(-1) higher in 2007 than the average of the two following years. Compared to 2009, digestibility was 89.5 g kg(-1) lower in 2007 and 39.9 g kg(-1) lower in 2008. There was correlation between digestibility and ash content (-0.94**), acid detergent fiber (-0.93**) and acid detergent lignin (-0.85*). Protein concentration was 15.2 g kg(-1) higher at the 20 cm spacing than at the 75 cm. No year x sowing density interaction was present, and sowing density did not affect DMY or forage quality. Sorghum DMY and forage quality were improved using a 33 seeds m2 sowing density and 20 cm row spacing.