Nutritional Composition Response to Yield Differences in Brown Midrib, Non-brown Midrib, and Photoperiod Sensitive Forage Sorghum Cultivars

The nutritive value of forage sorghums [Sorghum bicolor (L) Moench.] may be impacted by water application amount and forage sorghum (FS) type. Consequently, a two-year study examined the nutritional changes of different types of FS under dryland, two levels of deficit, and full irrigation. In 2003, four FS cultivars were tested: two brown midrib (BMR; BMR1 and BMR2), one Non-BMR, and one BMR-Photoperiod sensitive (PS-BMR) cultivar. In 2004, the same cultivars were tested with the exception of a non-BMR PS cultivar which replaced the PS-BMR cultivar. As water application and yield increased, forage quality decreased. Average in vitro true digestibility (IVTD) and neutral detergent digestibility (NDFD) declined 0.7 and 1.1 percentage points, respectively, with every 1 Mg/ha increase in yield (R² = 0.37 and 0.44, respectively). Neutral detergent fiber (NDF) tended to increase with increasing yield while crude protein (CP) tended to decrease. The BMR cultivars tended to maintain their forage quality at increasing yields better than the non-BMR cultivars. The PS cultivar showed the most rapid decline in forage quality as yield increased. The PS-BMR cultivar had improved forage quality at higher yields compared to the non-BMR PS cultivar. These results indicate that both FS cultivar and desired yield should be considered given production and nutritional goals.