Abstract
Field studies were conducted in 1980 and 1981 to characterize spring growth and tiller height characteristics of switchgrass (Panicum virgatum L.). Three cultivars (Cave-in-Rock (C), Pathfinder (P), and Blackwell (B)) were grown with 0 or 90 kg N ha−1. Tillers were harvested to a 10-mm stubble height on three dates at 1-wk intervals beginning in late May. Significant differences in spring growth and tiller characteristics were observed among cultivars. Tiller densities were lower for C (667 m−2) than for P (1141 m−2) and B (1180 m−2), but individual C tillers were larger because of greater leaf blade (406 vs. 238 and 230 mg for P and B, respectively) and stem (354 vs. 180 and 158 mg) weights per tiller. Mean stem yield per square metre for C (249 g m−2) was greater than for P (207 g m−2) and B (195 g m−2), indicating more rapid developmental growth and stem elongation of C, but no forage quality disadvantage for C when utilized for pasture because leaf blade yield per square metre was similar among cultivars and livestock graze selectively. Fertilization with N increased tiller density (B > P > C), leaf blade yield per square metre (+ 27%), and stem yield per square metre (+ 35%), the last because of hastened developmental growth and stem elongation. A linear increase in growth rate of leaf blade (18.0 g m−2 d−1 in 1980 and 8.9 g in 1981) and stem (23.7 g m−2 d−1 in 1980 and 10.4 g in 1981) was observed, the smaller rates in 1981 presumably because of cooler and drier growing conditions. Leaf tip, upper leaf collar, and apical meristem heights for C were always greater than for P and B, indicating that early or close defoliation would be more serious for C. Mean heights were increased from 23 to 31% by N fertilization. Daily rates of change were 2.12, 1.24 and 1.09 cm in 1980 and 0.78, 0.44 and 0.40 cm in 1981 for leaf tip, upper collar, and apical meristem heights, respectively.Key words: Switchgrass, Panicum virgatum L., stand density, dry matter yield, tiller characteristics, spring growth
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