Species and Nitrogen Effect on Growth Rate, Tiller Density, and Botanical Composition in Grass Hay Production.

Numerous studies have evaluated growth, stand dynamics, and botanical composition of grass swards separately, but little information is available on the interaction of these factors. The objectives of this study were to determine the response of growth rate, tiller density, and botanical composition in orchardgrass (Dactylis glomerata L.), smooth bromegrass (Bromus inermis Leyss.), and timothy (Phleum pratense L.) to different N levels. Growth rates ranged from 8.6 to 1.54, 9.14 to 0.67, and 4.19 to 0.29 g dry matter (DM) m(-2) d(-1) in orchardgrass, smooth bromegrass, and timothy. Orchardgrass growth rates responded to changes in abiotic conditions, while smooth bromegrass and timothy expressed less plasticity under favorable growth environments. All species exhibited temporal fluctuations in tiller density. Orchardgrass and smooth bromegrass tiller densities were not closely associated with yield, presumably because of compensation in tiller weight. Nitrogen did not affect tiller density during the first production year, but orchardgrass tiller density was influenced by N throughout the second production year, including the fall growth period, when tiller density in all species was affected. Aggressive growth rates in orchardgrass reduced species diversity by 65% by the end of the second production year. Total diversity in smooth bromegrass decreased from 7.2 to 3.5 species 0.25 m(-2) compared with an increase in timothy from 1.5 to 5.7 species 0.25 m(-2) due to a combination of slow growth and reduced tiller density. Orchardgrass and smooth bromegrass are superior to timothy in Northeast hay production systems because of greater DM production and less weed competition.