A study was undertaken at the University of Nebraska Agricultural Research and Development Center (central USA) to determine the effect of burning and harvest frequency on the vigour (measured as spring etiolated growth, basal cover and tiller density) of three frequently dominant prairie grasses (switchgrass Panicum virgatum, big bluestem Andropogon gerardii and indiangrass Sorghastrum nutans).
Field plots (nine 5 x 44 m plots; three replicates of each treatment) were established (using monocultures of each grass to avoid interspecific interactions) in 1986. From 1988 to 1991, treatments were applied to the same plots annually in a randomised complete block design:
Burning was undertaken in March, April, or May with unburned controls. Harvesting was undertaken once (June), twice (June and July), or 3-times (June, July and August) with unharvested controls. Harvesting comprised removal of grass in a 1 x 5 m area in each sub-subplot at each summer harvest using a flail-type forage harvester. The remaining 0.5 m² was mowed and cut material left for burning fuel.
To measure etiolated growth, three randomly selected plants per sub-subplot were clipped and covered with a metal can to exclude light. Etiolated growth was sampled 3-4 times each year (1989-1991) from mid-April when growth began, until it ceased in early July. Plant material was clipped to 2 cm. Number of etiolated tillers were counted. Clipped material was dried and weighed.
In 1991, tiller density (after July harvest) and basal area (in November) were recorded in sample quadrats.
Big bluestem produced 147% more etiolated biomass than switchgrass and 122% more than lndiangrass. Harvesting reduced grass vigour after 1 growing-season, but with little change thereafter. Etiolated biomass declined more (i.e. grass vigour decreased) as harvest frequency increased from two to three harvests than from one to two harvests (213, 205 and 162 g/m² for 1, 2, and 3 harvests/summer, respectively).
Harvest frequency increased tiller density; big bluestem (1,108/m²) produced more tillers than switchgrass (567/m²) and lndiangrass (830/m²). Burning stimulated tlllering (by an average 32% across all species and harvest treatments).
Big bluestem exhibited the most vigorous spring growth but switch grass produced more forage material. Burning did not affect grass vigour (as measured in this study), but it did decrease productivity.
If using or referring to this published study, please read and quote the original paper, this can be viewed at: https://www.uair.arizona.edu/holdings/journal/issue?r=http://jrm.library.arizona.edu/Volume51/Number1/