SWITCHGRASS LEAF APPEARANCE AND LAMINA EXTENSION RATES IN RESPONSE TO FERTILIZER NITROGEN

ABSTRACT

Quantification of effects from factors known to modify vegetative development and growth in grasses is important in modeling biomass yield. The objective of this study was to measure the effects of increasing levels of N on leaf appearance (LAR) and lamina extension rates (LER) in switchgrass (Panicum virgatum L.) under field and controlled environmental conditions. Five nitrogen (N) fertilizer rates (0 to 268 kg N ha⁻¹) were applied to a stand of “Alamo” switchgrass at Dallas, TX, and to potted plants (0 to 400 ppm) in a controlled environment. Quadratic regression models best described these responses to increasing rates of fertilizer N in both the field and controlled environment. In the field, LAR⁻¹ decreased to a minimum of 241 growing degree days (GDD) leaf⁻¹ at 163 kg N ha⁻¹ and LER increased to a maximum of 0.188 cm GDD⁻¹ at 164 kg N ha⁻¹. In the controlled environment, LAR⁻¹ decreased to a minimum of 155 GDD leaf⁻¹ at 90 ppm N and LER increased to a maximum of 0.272 cm GDD⁻¹ at 156 ppm N. Results demonstrate that LAR and LER are significantly affected by fertilizer N. Lamina extension rate responded to increasing levels of N in a manner typical of a classic yield response curve and was strongly correlated to plot yields, confirming its value as a potential indicator of yield.

ACKNOWLEDGMENTS

The research reported in this article is a portion from the thesis submitted by the senior author in partial fulfillment of the requirements for the M.S. degree from Texas A&M University—Commerce. Research sponsored by US Department of Energy under contract DE-AC05-96OR22464 with Lockheed Martin Energy Research Corporation.