Cultivar, Location, and Harvest Timing Effects on Switchgrass Production.

Switchgrass (Panicum virgatum L.), a native perennial warm-season grass species, has been the focus of much of the research efforts for lignocellulosic biofuel crops in the USA.  A study was conducted to determine the biomass production potential and evaluate agronomic traits of current and new cultivars/breeding lines of switchgrass.  Ten entries, including five breeding lines from the Noble Foundation and five commercial cultivars were evaluated at two locations (Raymond and Newton) in Mississippi during 2007 from a single end-of-season late-winter harvest.  At each location, the experimental design was a randomized complete block with four replications.  Due to their extremely poor stands at both locations, data from two commercial cultivars, ‘Kanlow’ and ‘Trailblazer,’ were excluded from analysis of the results.  There was a trend for location × entry interaction (P = 0.07) effect on dry matter (DM) yield.  At Raymond, all the breeding lines had greater DM yield (5.4 – 6.7 Mg ha^‑1) than ‘Cave-in Rock’ and ‘Shawnee’ (3.6 Mg ha^‑1 each), while that of ‘Alamo’ (4.4 Mg ha^‑1) was intermediate.  At Newton, DM yield of two of the breeding lines (9.3, 9.7 Mg ha^‑1) was greater than Alamo (5.7 Mg ha^‑1) and the other three breeding lines (5.7 – 7.0 Mg ha^‑1), and Cave-in-Rock (2.9 Mg ha^‑1) and Shawnee (2.2 Mg ha^‑1) were the lowest.  Yield of the two top entries at Newton was an average of 2.6 Mg ha^‑1 greater than at Raymond, while yields of all other entries were similar across locations.  There was a location × entry interaction (P = 0.02) effect on plant height, mainly caused by the separation of differences among cultivars at each location.  Plants of all entries were taller at Newton.  At both locations, Cave-in-Rock (0.95 m, Raymond; 1.15 m, Newton) and Shawnee (0.96 m, Raymond; 1.31 Newton) were shorter than all the other entries. At Raymond, Alamo (1.47 m) and the breeding lines (1.43 – 1.48 m) had equal height, while at Newton, Alamo (1.84 m) was intermediate between the two shorter commercial cultivars and the taller breeding lines (1.93 – 2.15 m).  Late fall vs. late winter harvest treatment was imposed at Raymond, with season of harvest as a split plot of the original randomized complete block design.  Averaged across entries, late fall yield (5.9 Mg ha^‑1) was greater (P = 0.02) than late winter yield (5.3 Mg ha^‑1), and average plant height followed a similar pattern (1.42 m in late fall vs. 1 .34 m in late winter).  The study will be continued for two more years.