CHEMICAL-REGULATION OF GROWTH, YIELD, AND DIGESTIBILITY OF ALFALFA AND SMOOTH BROMEGRASS

In addition to enabling manipulation of plant growth and development, growth regulators have potential for increasing forage digestibility. This study focuses on the use of gibberellic acid (GA3), alpha-naphtha lene acetic acid (NAA), 6-benzylaminopurine (BA), o-benzylhydroxylamin e (OBHA), and monocetyl phosphate (C16P) to alter growth, dry weight ( DW) yield, and in vitro digestible dry matter (IVDDM) of forage grasse s and legumes grown in a greenhouse. Screening experiments revealed th at GA3, NAA, and OBHA at rates of 1.6, 160, and 0.51g a.i. ha(-1), res pectively, were more effective in altering regrowth of potted alfalfa (Medicago sativa L.) and orchardgrass (Dactylis glomerata L.) compared with other treatments. Subsequent experiments with increasing dosages of GA3, NAA, and OBHA on alfalfa and smooth bromegrass (Bromus inermi s Leyss.) confirmed that these regulators can be used to manipulate fo rage growth. Increasing concentrations of GA3 increased growth and DW yield but decreased IVDDM, whereas high concentrations of NAA decrease d growth and DW yield but increased IVDDM. OBHA treatments resulted in little or negative change in IVDDM. Results generally showed that pla nt growth regulators can be used to manipulate forage growth, but that there is a trade-off between herbage yield and digestibility of forag e tissues.