Cutting Height and Heat Stress Affect Orchardgrass (Dactylis glomerata L.) Regrowth Vigor.

Producers of orchardgrass hay in the Mid-Atlantic U.S. have observed a reduction in regrowth vigor and a decline in the persistence of their swards.  Cutting height and temperature are important determinants of cool-season grass regrowth.  We hypothesize that high temperature and low cutting height will interact to limit regrowth rate.  Orchardgrass plants were cut to either 2.5 or 7.5 cm and then placed into environmentally-controlled chambers with constant temperature of 20 or 35 degrees C (n = 3).  Stubble was harvested on days 0, 1, 3, and 11 following cutting and analyzed for water- and ethanol-soluble carbohydrates, starch, chlorophyll, protein, free amino acids, ammonium, and nitrate.  Photosynthesis, transpiration, stomatal conductance, and chlorophyll fluorescence were measured on the regrown leaves on days 3 and 11, and regrowth biomass was measured on day 11.  Ethanol- and water-soluble carbohydrate concentrations declined following cutting, and photosynthesis was reduced by the high temperature treatment.  Both cutting height and temperature significantly affected regrowth biomass with control temperature and high cutting height resulting in the greatest regrowth and high temperature and low cutting height resulting the least.  The effects of low cutting height in orchardgrass are compounded by high temperature following harvest.  Slowed regrowth during summer may allow for further heat stress, tiller death, and the reduced persistence of orchardgrass swards.