The Relationship Between Yield and in Vitro True Digestibility for Summer Annual Grasses Commonly Grown in the Mid-Atlantic Region of the United States.

Trials conducted at Virginia Tech’s Southern Piedmont Agricultural Research and Extension Center in 2009, 2010, and 2011, evaluated the yield and digestibility of summer annual grass varieties including conventional and BMR forage sorghums species and pearl millet.  Plots were established in early June and harvested when the average height was 0.75 m.   Total yield was ranged from 5,512 to 9,303, 4,119 to 5,945, 8,196 to 13,405 kg ha^-1 in 2009, 2010, and 2011, respectively.  Average over harvests, in vitro true digestibility also varied, ranging from 59 to 76% and 66 to 76% for the 2009 and 2010 growing seasons, respectively.   What was most interesting is that the highest yielding variety in the trial was also one of the most digestible.  This indicates that high yield and digestibility may not be mutually exclusively traits.  To better understand how to use yield and digestibility data when selecting or recommending a summer annual grass species-variety, the difference from average for the yield and digestibility was graphed and the graph was divided into four quadrants.  The upper right hand quadrant includes varieties that have above average yield and digestibility.  These species-variety combinations would be the most desirable to include in a forage production system.   In contrast, the bottom left hand quadrant contains species-variety combinations with below average yield and digestibility.  These varieties would likely be the last choice for including in forage production programs.