Yield Accumulation, Leaf Area Index, and Light Interception of Smooth Bromegrass1

Abstract

Smooth bromegrass (Bromus inermis Leyss.) is a cool‐season grass used extensively in the midwestern USA for spring and fall grazing. Smooth bromegrass has limited production in this region during the summer. This study was conducted to document the growth characteristics and yield accumulation of smooth bromegrass under various levels of N fertilizer. Live yield (dry matter yield of living herbage), leaf area index (LAI), light interception (LI), and crop growth rate (CGR) were determined on an established stand of ‘Lincoln’ smooth bromegrass grown on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudolls) in eastern Nebraska. Zero, medium, and high N levels were maintained at each growth period. Irrigated spring, summer, and fall growths of smooth bromegrass were sampled at 1‐ or 2‐week intervals in 1981 and 1982 depending on growth rate. Live yield, LAI, and CGR were all highest in the spring. Live yield reached a maximum of 10.3 Mg ha−1, CGR reached a maximum of 190 kg ha−1 day−1, and LAI reached a maximum of 6.8, which intercepted up to 99% of the incoming photosynthetic photon flux density during the spring growth period. Summer values for maximum live yield, LAI, and LI were 3.2 Mg ha−1, 4.1, and 73%, respectively. Maximum values of live yield, LAI, and LI for the fall growth period were 2.8 Mg ha−1, 5.2, and 97%, respectively. Smooth bromegrass has different growth and canopy characteristics at different seasons of the year. Growth models should consider seasonal differences in canopy characteristics as well as environmental parameters.