Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 7/10/1995
Publication Date: N/A
Technical Abstract: Switchgrass (Panicum virgatum L.) is a C4 grass reported to be productive with low to moderate rates of N fertilization. The objective of this research was to examine the effect of N fertilization on growth and photosynthetic efficiency of switchgrass. Annual N fertilizer rates ranging from 0 to 250 kg N/ha were applied in up to four split applications comprising nine treatments. Dry matter (DM) yield was determined at each of three harvests (late May, mid July and early September). Photosynthetic efficiency was estimated using the initial slope of the response curve of CO2 assimilation rate to intercellular partial pressure of CO2. Nitrogen applications increased DM yield from 4,829 to 9,087 kg/ha in a dry year and from 6,559 to 12,286 kg/ha in a year with adequate rainfall. There was no effect of splitting applications of N fertilizer on total dry matter yield and little increased yield above 100 to 150 kg N/ha. Increased yield was related to photosynthetic efficiency in the third (r2 = 0.69), fourth (r2 = 0.78), and fifth (R2 = 0.93) fully expanded leaves.