Dormant-Season Plantings, Seeding Rates and Seed Dormancy Affects On Switchgrass Establishment and Yield.

Establishment success is arguably the greatest agronomic challenge to wide-scale switchgrass (Panicum virgatum L.) feedstock production on marginal lands in the Southeastern U.S.  Some failures have been linked to seed dormancy, a common trait in this species; one strategy for breaking dormancy is dormant-season planting. The objective of this study was to evaluate the efficacy of dormant-season planting to enhance switchgrass establishment in the Southeast by: i) evaluating three dormant-season planting dates versus a growing-season control; ii) evaluating two seeding rates for dormant-season planting; and, iii) comparing high and low dormancy seed lots for both rate and date combinations. Four planting dates (1 December, 1 February, 15 March, and 1 May), two seeding (6.7 and 10.1 kg PLS ha^-1), and dormancy rates (high, 45 and 75%; low, 2 and 5%, 2009 and 2010, respectively) were assigned in a split-block design with three replications at two locations in Tennessee from 2009-2011. All four seeding rate by dormancy level combinations were the split plots and seeding date was the whole plot. Planting date, seeding rate, or dormancy did not significantly influence yields for two years at one location (P <0.05). However, density of March plantings equaled or exceeded those of other dates for all locations and years. Density was not affected by seeding rate or seed-dormancy level. Therefore, higher seeding rates for dormant-season planting are not necessary or cost-effective. Conversely, our results suggest that March planting offers increased reliability and flexibility for establishment with either high or low dormant seed lots. Dormant-season planting also suggests in-situ stratification is a viable option for high-dormancy seed lots. However, results need to be validated over a broader range of soils and climatic conditions, especially along a winter severity gradient.