INTEGRATION OF IRON AND TRINEXAPAC-ETHYL INTO NITROGEN FERTILIZATION REGIMENTS FOR MANAGING FERTILIZER AND WATER REQUIREMENTS OF PENN A-SERIES CREEPING BENTGRASS (<i>Agrostis stolonifera</i> L.) PUTTING GREENS
Open Access
- Author:
- Dai , Jing
- Graduate Program:
- Agronomy
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 21, 2010
- Committee Members:
- Alfred J Turgeon, Dissertation Advisor/Co-Advisor
Alfred J Turgeon, Committee Chair/Co-Chair
James Landis Rosenberger, Committee Member
Maxim J Schlossberg, Committee Member
David Robert Huff, Committee Member
John Matthew Schmidt, Committee Member - Keywords:
- trinexapac-ethyl
nitrogen
iron
creeping bentgrass - Abstract:
- Creeping bentgrass (<i>Agrostis stolonifera</i> L.), the most commonly used cool-season turfgrass for surfacing putting greens in temperate and subtropical regions, requires regular nitrogen (N) inputs to maintain visual quality and replenish nutrients removed under daily mowing regiments. Nitrogen fertilizers, especially those applied to porous sand-based putting green root zones; pose a threat to groundwater quality due to leachate NO<sub>3</sub><sup>-</sup> pollution. Meanwhile, liberally applied N is associated with excessive clipping production, reduced putting green speed, decline in root growth, and exacerbated summer stresses. Research indicated that some N requirements can be substituted by iron (Fe) fertilization with equivalent visual quality and that lower N inputs are directly associated with lower evapotranspiration and consequently less water requirements. Trinexapac-ethyl (TE), a gibberellic acid inhibitor, is known to reduce clipping yield and promote turfgrass tolerance to environmental stresses. We thus hypothesize that N and water fertilizer requirements of creeping bentgrass putting greens can be reduced by TE and Fe treatments and that better rooting, fewer clippings, faster putting green speed, and more drought resistance may also be obtained with reduced N fertilization and concurrently applied Fe and TE. Field experiments in 2007 and 2008 were conducted simultaneously on Penn A-series creeping bentgrass putting greens based on United States Golf Association (USGA) specified sand and on a Hagerstown silt loam. Field experiments conducted in 2007 investigated the partial substitution of N by Fe in the fertility programs of ‘Penn A-4’ creeping bentgrass putting greens. Both sand- and soil-based putting greens were treated with combinations of Fe rates ranging from 0 to 4.9 kg ha<sup>-1</sup> mo<sup>-1</sup> (as FeSO<sub>4</sub>∙7H<sub>2</sub>O) and N from 15.5 to 43.1 kg ha<sup>-1</sup> mo<sup>-1</sup> (as NH<sub>4</sub>NO<sub>3</sub>), every 6 or 12 d, from May to October. Fertilizer rate combinations were arranged in a response surface design while application frequencies in a strip design, with a total of 144 experimental plots. Turfgrass color, canopy density, clipping yield, tissue nutrients/carbohydrates, and rooting parameters were measured to evaluate growth and visual quality. Field experiments conducted in 2008 investigated the effects of combined N, Fe and TE treatments on turfgrass quality and N requirements of ‘Penn A-1/A-4’ creeping bentgrass putting greens. Both sand- and soil-based putting greens were treated with factorial combinations of three NH<sub>4</sub>NO<sub>3</sub> rates (15, 30, or 45 kg N ha<sup>-1</sup> mo<sup>-1</sup>), three FeSO<sub>4</sub>∙7H<sub>2</sub>O rates (2.5, 5, or 7.5 kg Fe ha<sup>-1</sup> mo<sup>-1</sup>), and three TE application frequencies (every 5, 10, or 15 d, at the rate of 0.102 kg ha<sup>-1</sup> mo<sup>-1</sup>), from May to October. Fertilizer treatments were applied every 10 d. These experiments were arranged in an incomplete block design with a total of 120 experimental plots. Irrigation was largely suspended in two extended periods and practiced only to prevent severe dehydration. Turfgrass color, canopy density, clipping yield, leaf water content, ball roll distance, rooting parameters, tissue nutrients, and carbohydrates were measured to evaluate growth, visual quality, and stress tolerance. Nitrogen was the major driver for shoot growth and leaf carbohydrate accumulation in both years but significantly inhibited root growth at higher rates in 2007. Greener turfgrass color was observed at the combination of high Fe and N rates. Iron rates higher than 2.5 kg ha<sup>-1</sup> mo<sup>-1</sup> are more likely to produce synergistic effects on turfgrass color with N applications. Iron had generally limited effects on clipping yield but appeared to reduce shoot growth at higher N rates. Iron reduced canopy density regardless of N rate in both years. The root growth inhibition observed at higher N rates appeared to be relieved with Fe fertilization in 2007, which was probably related to the shoot growth regulation effects of Fe. Nitrogen and Fe fertilizers applied every 6 d produced more stable responses in turfgrass color and canopy density than when applied every 12 d in 2007. The three TE application frequencies did not affect most of turfgrass growth and quality parameters in 2008. The difference among the closely spaced TE reapplication intervals may have been too subtle to detect under field conditions. According to our field studies in 2007 and 2008, we recommend to substitute part of the N requirements of Penn A-series creeping bentgrass putting greens with 4 to 6 kg Fe ha<sup>-1</sup> mo<sup>-1</sup> to manage N inputs around 25 to 35 kg ha<sup>-1</sup> mo<sup>-1</sup> for less shoot growth, greener turfgrass color, better rooting, and less water requirements. Reduced canopy density may occur with reduced rates of N and more input of Fe but canopy density should stay in the acceptable range with moderate N inputs, as observed in our field studies. Our research suggests that the partial substitution of N with Fe minimizes the negative impact associated with intensive N fertilization while maintaining optimum turf quality.