The impact of maturity stages on yield, quality, and nutritive value of ensiled Johnsongrass [Sorghum halepense (L.) Pers]

Johnsongrass (Sorghum halepense (L.) Pers.] is a non-native, invasive species that causes substantial losses in row crops and hay fields, which could be minimized by using Johnsongrass as a conserved forage. Two experiments were conducted to evaluate the yield and quality of Johnsongrass ensiled at four maturities: harvested every 3 weeks (3WK), boot stage (BOOT), flower stage (FLOWER), and dough (DOUGH) stages. In experiment 1, yield, botanical composition, nutritive value, and fermentation characteristics of Johnsongrass were measured. In experiment 2, Johnsongrass silage was incubated for 48 h for assessment of gas production, pH, in vitro dry matter digestibility (IVDMD), and volatile fatty acids. The experimental area consisted of 16 plots (2.74 m x 4.57 m) divided into four blocks, and treatment was randomly assigned to plot within block. Each year, silage was prepared for each plot from the two cutting closest to July 1. After 10 weeks, the silos were opened, and silage samples were frozen for further analysis. Data from both experiments were tested for the effects of maturity stage and harvest timing (first and second harvest). The results from experiment 1 showed an increase (P < 0.0001) in dry matter yield from 3WK stage to DOUGH. Johnsongrass, as a proportion of the total botanical composition, declined at the end of the growing season for 3WK but increased in FLOWER (P = 0.0010). In the first harvest, 3WK and BOOT stage silages had the greatest concentrations of crude protein and total digestible nutrients and lowest of fiber (neutral detergent fiber and acid detergent fiber; P < 0.0001). In the second harvest, differences in nutrient content were significant only for 3WK silages, which showed the best nutritive value (P < 0.0001). In experiment 2, IVDMD of silage followed the same trends described for nutritive value from experiment 1. Overall, these results demonstrate that Johnsongrass can be successfully ensiled, but to optimize forage nutritive value and quantity, Johnsongrass should be ensiled before it reaches the flower stage.