Impacts of Environmental and Management Factors on Gibberellin Production in Turfgrass.

Many different environmental and management factors impact shoot growth in turfgrasses. Fertilizer, water, temperature, humidity, and pesticides can affect the rate at which the leaf elongates, which is likely the result of changes in gibberellin production. The goal of our research is to create gibberellin production models to increase fertilization precision and manage turfgrass clipping production.

Growth rate of three species of turfgrasses, ‘T1’ creeping bentgrass (Agrostis stolonifera Hud.), ‘NuDestiny’ Kentucky bluegrass (Poa pratensis L.), and ‘7-Iron’ perennial ryegrass (Lolium perenne L.), were evaluated in two growth chambers. The day/night air temperatures in the cool growth was 23/17C and 33/27C in the hot growth chamber. Other conditions were similar in both chambers including a 14-h photoperiod (600 μmol PAR m^-2 s^-1) and 70% relative humidity. Plugs from each species were taken from the East Campus Turf Plots and split between the hot and cold chambers. The 5 cm diameter plugs were fertilized with urea at 5 kg N ha^-1 -28d, -21d, and -14d before treatments were initiated. Four nitrogen fertilizer rates were applied weekly each species within the hot or cold chambers. Fertilizer rates included 0, 6, 12, 24 kg N ha^-1 from urea for the duration of the study. Treatments and species were replicated four times. Weekly clipping collection began day 14 after the first fertilizer treatment and continued for five weeks. After five weeks, the canopy of all the plugs was harvested for GA extractions.

Perennial ryegrass in the cool chamber had three times greater clipping yield than in the hot chamber. Conversely, creeping bentgrass yield was not affected by chamber temperature. Kentucky bluegrass and bentgrass both had a greater N rate responses than perennial ryegrass. Among all species, the fertilizer rate responses were greater in the cool chamber. These results will help direct summer fertilization programs.