PhD Oral Examination: Miyuan Xiao


Interested Members of the University Community are invited to attend the Final Oral Examination for the Degree of Doctor of Philosophy of Miyuan Xiao of the Department of Plant Agriculture

Date: Monday, November 25, 2019 
Time: 9:30am 
Location: CRSC202

Thesis Title: Turfgrass Water Use and Growth under Low Mowing Heights and Different Nitrogen, Phosphorous, and Drought Conditions

Advisory Committee   
Dr. Eric Lyons, Advisor 
Dr. Hugh Earl
Dr. Katerina Jordan
Dr. Youbin Zheng

Examination Committee
Dr. Gale Bozzo
Dr. Guillaume Grégoire (External - Université Laval)
Dr. Eric Lyons
Dr. Hugh Earl
Dr. Bernard Grodzinski                                   


Water use of low-cut turfgrass at different heights of cut (HOC) or different fertility levels is not known, and information on turfgrass performance during different water deficit conditions is limited. The effects of HOC (3 vs. 5 mm), nitrogen (N) levels prior to drought (0.8, 4.0, 8.0, and 1.6 g total N m-2for 60 d), phosphorus (P) level (1.1 g total P m-2vs. no P), and turfgrass variety (‘L93’ and ‘Penncross’ creeping bentgrasses, annual bluegrass, and ‘SR7200’ velvet bentgrass) under three drought conditions (no drought, periodic drought, and prolonged drought, including a drought recovery phase) on turfgrass growth, net carbon exchange rate (Pn rate), and root parameters were measured through three separate experiments. Real-time water consumption using mini-lysimeter load cell arrays under three drought conditions was also measured. The novel mini-lysimeters were able to detect weight changes of 25.3 cmpots containing grass at 1-min intervals, and evapotranspiration (ET) differences between treatments at 1-h intervals. The 5 mm HOC resulted in ~8% more water use than the 3 mm HOC for full cover turfgrass with sufficient irrigation. Turfgrass at 5 mm HOC had higher color ratings, Pn rate, and water use efficiency than turfgrass at 3 mm HOC at the beginning phase of drought. Higher HOC resulted in a faster decrease of hourly ET than lower HOC under drought conditions due to greater water consumption and lower water availability. The 8 g m-2 total N level resulted in better turf performance and more water use than lower N rates. However, 16 g m-2total N did not improve turf growth from the 8 g m-2 total N level. Increasing N rates improved drought tolerance (measured through Pn rate) during drought and post-drought recovery periods. Turfgrass varieties respond differently to P levels under drought. Low P may improve drought tolerance for ‘Penncross’ creeping bentgrass, whereas high P may lead to better drought tolerance for ‘SR7200’ velvet bentgrass. These findings contribute to the understanding of turfgrass under periodic or prolonged drought conditions and couldlead to the use of better predictive models for managing water use by turfgrass managers.