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FORAGE & GRAZINGLANDS

How Does Plant Population Density Affect the Yield, Quality, and Canopy of Native Bluestem (Andropogon spp.) Forage?

USDA-ARS, Southern Plains Range Research Station, 2000 18th St., Woodward, OK 73801

^* Corresponding author (tspringer{at}spa.ars.usda.gov)

The density at which a crop is grown is known to affect its growth and quality, but little is known about how plant density affects the growth of native perennial forage grasses. The objectives were to investigate the effects of plant population density on the forage yield, forage quality, and plant canopy structure of two native bluestem species. Big bluestem (Andropogon gerardii Vitman) and sand bluestem (A. hallii Hack.) were established at six plant densities (1.2, 1.8, 2.7, 3.6, 5.4, and 10.8 plants m^–2) in a split plot experiment with whole plots in four randomized blocks. Plant density was the main plot and bluestem species was the split plot. Data were analyzed with a mixed model analysis of variance with blocks within year as random effects and year as a repeated measure. The optimum plant density for forage production was between 3.6 and 5.4 plants m^–2. However, the optimum for crude protein (CP) concentration occurred at 1.2 and 10.8 plants m^–2 and followed a quadratic response as plant density increased. The greatest leaf area index (LAI; leaf area per square meter) was at 10.8 plants m^–2. At 10.8 plants m^–2, the average yield loss from maximum was about 8.5% dry matter (DM). Also, the CP concentration was 8.5% greater for plants grown at 10.8 plants m^–2 than for those grown at 3.6 to 5.4 plants m^–2. A plant density of 10.8 plants m^–2 would produce high quality forage with only slight reductions in DM yield as compared with plants grown at 3.6 to 5.4 plants m^–2.

Abbreviations: CP, crude protein • DM, dry matter • IVDMD, in vitro dry matter digestibility • LAI, leaf area index • LTA, long-term average