Efficient Irrigation for Recreational Turf In the Cool-Humid Northeast: II. Effects of Nitrogen and Height of Cut On Rooting, ET and Kc Values.

Crop coefficients (Kc) are used in association with weather station reference evapotranspiration (ET0) to predict actual ET rates (ETa). Efficient scheduling of irrigation requires reliable Kc values. Practices such as height of cut (HOC) and nitrogen (N) fertility can alter ETa and rooting thus influencing Kc values (calculated as ETa/ ET0) and irrigation scheduling. The objective of this study was to compare the effects of N and HOC on ETa, rooting and Kc values for creeping bentgrass (Agrostis stolonifera L., CBG) maintained as green and fairway turf, and Kentucky bluegrass (Poa pratensis L., KBG) and perennial ryegrass (Lolium perenne L., PRG) maintained as sports turf. Species main plots were arranged as a complete factorial with two N levels, 98 and 196 kg N ha-1 yr-1, using four replicates arranged as a RCB design. All species by N main plots were split according to two HOC with sports turf maintained at 31.25 and 62.5 mm HOC and golf turf maintained at 3.125 and 9.375 mm HOC. Twenty-three daily ETa (using weighing lysimeters), ET0 (using FAO 56 equation), Kc values, and leaf extension rates were measured during the summer months beginning 21 June and ending 31 August, 2010. Root dry weights were also measured in July and August at four depths (0 to 10 cm, 10 to 25 cm, 25 to 45 cm and 45 to 65 cm). HOC was the single most important practice affecting ET and rooting across the three species but not within the species. Relative ranking of rooting at depths greater than 10 cm were PRG > KBG = CBG, while ranking of ETa (and Kc) and leaf growth rates were KBG = PRG > CBG. Fertilizer N (82% as slow release N) had little to no effect on any measured variables in summer.