SWITCHGRASS GROWTH AND DEVELOPMENT IN RESPONSE TO WATER, NITROGEN, AND PLANT DENSITY

Authors: Sanderson, Matt; REED, R - SAMUEL R NOBLE FOUNDATION

Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/1999
Publication Date: 4/20/2000
Citation: Sanderson, M.A., Reed, R.L. 2000. Switchgrass growth and development in response to water, nitrogen, and plant density. Journal of Range Management. 55:221-227.

Interpretive Summary: Switchgrass is a warm-season perennial grass native to much of North America. It is commonly grown in the Great Plains for harvested forage and grazing. Recent interest in using switchgrass as a biomass energy crop has created new questions about how resource inputs (such as water and nutrients) affect growth, development, and plant relations in switchgrass populations. The objective of our study was to examine how resource input affected competition among plants in switchgrass. Our results show that competitive responses of switchgrass plants at high plant densities are controlled by competition for light because plant yield and morphology at high densities were not affected by irrigation or nitrogen inputs. This concept has practical application in managing stands of switchgrass that have decreased in density by natural thinning or mismanagement. If stands have thinned to a point at which individual plants are not able to compensate by increased tillering, more external inputs may be required to maintain productivity, or the stand must be re-established.

Technical Abstract: Switchgrass (Panicum virgatum L.) is an important perennial component of the tallgrass prairie and is a productive warm-season forage grass. Interest in growing switchgrass as a biomass energy feedstock has raised questions about efficient resource use during production. The objective of our study was to examine how resource inputs affected interspecific plant competition in switchgrass. 'Alamo' switchgrass was established in nonweighing lysimeters in May 1993 and grown under two N fertilizer levels (22 and 112 kg N ha-1) and under field capacity and water-deficit conditions during 1993 to August 1994. Plant spacing varied systematically from 10 to 70 cm. Plants were harvested in late summer each year and yield, tiller number, leaf area, and morphological development stage were measured. As plant spacing increased, tiller number, leaf area, yield, and morphological development stage increased. Yield, leaf area, and tiller number of plants in the establishment year did not respond to high N input (and perhaps water input, but the water deficit periods may not have been as severe as in 1994) but did respond to increased plant spacing. Established plants, however, did respond to high N input at low plant densities in 1994 with increased leaf area and greater plant yields compared to the low-N treatment. The increased yield per plant at high N input resulted from increased individual tiller size and not increased tiller number. Our data indicate that competitive responses of switchgrass plants at high plant densities are controlled by competition for aboveground resources (principally light), as plant yield and morphology at high densities were not affected by water or N inputs.