Compensatory Yield Responses of Young Native Warm-Season Grass Stands to Seasonal Changes in Harvest Frequencies

Abstract

Defoliation management can significantly affect subsequent grassland’s forage productivity and sustainability. To assess the type and persistence of native warm-season grass (NWSG) yield responses to changes in defoliation intensity, a five-year harvest trial was conducted, in a randomized complete block design, at Virginia State University’s research farm. Yield responses of newly established indiangrass (Sorghastrum nutans L.). Nash, big bluestem (Andropogon gerardii Vitman), switchgrass (Panicum virgatum L.) and eastern gamagrass (Tripsacum dactyloides L.) stands to second-year changes in harvest regimes were monitored. In 2012, seedlings of these native grasses were transplanted in clean-tilled plots, with 16 plants in each pot. The field was not irrigated, but broadleaf weeds were manually controlled, and all plots were mowed in August and mid-November of 2013. Starting June 2014, each plot had three harvest-strips assigned to single, two, or three cuts per year from early June to mid-October using a plot-harvester; forage weights were recorded. Based on the recorded fresh and oven-dry sample weights, plot forage DM yields were estimated. Cumulative forage biomass of all three-cut strips flipped to single-cut increased by ≥30% and >50% for big bluestem. The second-year single-cut yields also outperformed those cut thrice since the first year by 22–51%. The second-year biomass increases from single-cut strips that were cut thrice in the first year demonstrated that flipping-triggered compensatory yield responses overshadowed the first- year losses in plant vigor. The compensatory yield increases continued to, but not beyond, the third year and varied between species. The yield responses also showed that magnitudes of defoliation management–triggered NWSG growth responses depend more on growing conditions during the recovery period than its actual duration.