Nitrogen (N) is the nutrient used in greatest quantity by plants and, consequently, is the element around which most turfgrass fertility programs are centered. Nitrogen is a component of many of the biochemical constituents of plants, including chlorophyll, amino acids, proteins, enzymes, vitamins, and many other materials critical to their function (Christians, 1998). When conditions are favorable, N applications to turfgrass result in stimulated shoot growth. It has been reported in some previous studies that turfgrass evapotranspiration rates increase with increasing N fertilization, a relationship often attributed to changes in leaf elongation rate and/or the amount of transpiring leaf area exposed to the atmosphere between mowings (Ebdon et al., 1999; Feldhake et al., 1983; Green et al., 1990; Krogman, 1966; Mantell, 1966; Shearman and Beard, 1973). The grass species used in these previous studies have usually been mowed on a weekly basis at heights exceeding 25 mm.
One approach to counter high evapotranspiration rates of well-growing, highly maintained turfgrass may be the application trinexapac-ethyl (TE), a plant growth regulator (Watschke et al., 1992). TE interferes with gibberellin biosynthesis and reduces laminar cell elongation, thereby decreasing the need for frequent mowing (Adams et al., 1992). Also, TE application induces production of shorter, thicker cells (Ervin and Koski, 2001b), increased specific leaf weight (Gaussoin et al., 1997; Heckman et al., 2001), increased tillering (Beasely et al., 2005; Ervin and Koski, 1998; Fagerness and Yelverton, 2000; Goss et al., 2002), and changes in total root length and surface area (Beasely et al., 2005). By decreasing canopy height through suppression of vertical shoot elongation, one consequence may be a decrease in evapotranspiration rates. TE is reportedly capable of reducing turfgrass water use by up to 25% (Syngenta Professional Products, 2008).
Although there have been some previous studies concerning the influence of TE on turfgrass evapotranspiration rates, these have mainly involved higher-cut, upright-growing grass species. Furthermore, results have been somewhat contradictory. TE applications were found to decrease evapotranspiration rates by 11% in a 6-week greenhouse study with tall fescue (Festuca arundinacea Schreb.) (Marcum and Jiang, 1997) and by 20% in a mixed stand of kentucky bluegrass (Poa pratensis L.) and tall fescue (King et al., 1997). However, when averaging an entire 3-year field study, Ervin and Koski (2001a) determined that TE applications (applied every 6 weeks) were ineffective at decreasing kentucky bluegrass evapotranspiration rates, only reducing evapotranspiration on 5 of the 34 weeks of the study. Furthermore, correlation analysis did not show any relationship between clipping dry weight and evapotranspiration rates.
More recently, pretreatment with TE (applied 14 d before imposition of stress) was found to enhance quality of creeping bentgrass during combined drought and heat stress (McCann and Huang, 2007). However, the effects of TE on evapotranspiration in the study were not clear. Although TE-treated and nontreated turf had similar rates of evapotranspiration under nonstressed conditions, TE-treated plants had lower evapotranspiration rates 10 d after imposition of drought and heat stress (24 d after TE application) but higher evapotranspiration rates 11 d later (35 d after TE application). The timing of TE pretreatment and associated postsuppression rebound growth effects (which often occur 4 to 6 weeks after application) likely coincided with the stress period in the study, making it difficult to sort out the actual effects of TE.
Resolution of the effects of N rate and TE on evapotranspiration rates of prostrate grass species, specifically creeping bentgrass and bermudagrass, maintained at lower heights of cut (less than 10 mm) has not been explored. The height and growth habit of a turfgrass may confound the influence of these cultural factors on evapotranspiration because lateral-growing, prostrate species are not exposed to as turbulent airflow as might be experienced by grasses with a more upright growth habit such as tall fescue and kentucky bluegrass (Huang, 2008; Kim, 1983). As a result of their prostrate growth pattern, these species may not benefit as greatly from cultural factors aimed at reducing vertical leaf elongation. The objective of this study was to investigate the individual and interactive effects of TE application and N rate on growth and evapotranspiration of ‘Penncross’ creeping bentgrass (Agrostis stolonifera L.) and ‘Tifdwarf’ bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davy].
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Syngenta Professional Products 2008 Primo MAxx® pgr linked to fuel and labor savings 2 Sept. 2008 <http://syngentaprofessionalproducts.com/news_releases/news.aspx?id=80783>.
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