Date of Award

5-2008

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Plant and Environmental Science

Advisor

Liu, Haibo

Committee Member

McCarty , Lambert B

Committee Member

Toler , Joe E

Abstract

Potassium (K) is an essential plant nutrient commonly applied to increase creeping bentgrass tolerance to environmental stresses and maintain overall turfgrass stand health. Limited research defining the K requirement of creeping bentgrass under heat and drought stress exists. Furthermore, research investigating K, calcium (Ca), and magnesium (Mg) recovery under abiotic stress has been inconsistent. To build on previous research and investigate the differences between liquid and granular K fertilization, experiments were conducted to evaluate the performance of liquid and granular K carriers in conjunction with liquid calcium and magnesium on their ability to suppress summer bentgrass decline of creeping bentgrass (Agrostis stolonifera L.) grown in the transition zone of the United States.
A field experiment was conducted from May 2006 to October 2007 to investigate liquid and granular K fertilization on turfgrass quality, clipping yield, chlorophyll, root weight, volumetric soil water content and leaf and root nutrient concentrations of 'Crenshaw' creeping bentgrass. Treatments consisted of two annual potassium rates, 0 and 195 kg K ha-1 yr-1, in liquid and granular forms, with either liquid calcium (49 kg ha-1 yr-1), liquid magnesium (49 kg ha-1 yr-1), or both. Liquid K applications significantly reduced visual quality of bentgrass during 2006. Turfgrass quality in 2007 was unacceptable (<7) for the months of June, August, and September, while only plots receiving Ca without K produced acceptable turf. Clipping yield was also significantly decreased under liquid K in August and November 2006, while calcium produced the greatest yield in July and August 2006 and September and October 2007. 'Crenshaw' creeping bentgrass treated with liquid K produced 8 and 16% greater clipping K concentration in August and November 2006 and 11 and 21% greater tissue K content by June and October 2007 compared to untreated.
Another two year field study was conducted from May 2006 to October 2007 to determine the performance of two K carriers (liquid and granular) under rates of 0, 98 and 195 kg ha-1 annually and a wetting agent (WA) at 19.09 L WA ha-1 monthly. Data concerning visual turf quality, clipping yield, root weight, soil moisture, soil hydrophobicity, and leaf and root tissue nutrient concentrations were recorded. Turf quality was improved by the high rate of granular K; however, quality significantly declined for turf receiving the higher liquid K rate throughout 2006 from phototoxic effects of foliar K fertilizers. Wetting agent decreased turf quality in 2006 partially due to excess soil water retention but creeping bentgrass quality was improved under drought conditions in 2007 with the addition of WA. In August and November 2006 and June and October 2007, liquid K at 195.29 kg ha-1 produced greater leaf tissue K concentrations compared to untreated. Liquid K at the 195.29 kg ha-1 rate adversely affected root weight in August 2006 and October 2007 by 36% and 20%, respectively, while yearly declines in root weight of all treatments were noted. Soil hydrophobicity decreased by 19.92 and 7.16 units at 1.5 cm in 2006 and 2007, respectively, and declined by 8.86 and 6.64 units at 3.0 cm in 2006 and 2007, respectively, with the addition of the WA.
A third field study was conducted from November 2006 to February 2008 to examine the interactive effects of nitrogen (N) and iron (Fe) fertilization on rough bluegrass (Poa trivialis L.) overseed stands under reduced light environments. Treatments included three annual N rates of 49, 98, and 147 kg N ha-1 yr-1 split between 4 applications during the winter months. Fe was supplied simultaneously at 10.8 kg a.i. ha-1 per season. Shade treatments included full sunlight and 55% shade and were applied daily. Data collection included turf quality, clipping yield, chlorophyll, and clipping nutrient concentrations. In this experiment, turf quality was improved with increased N rate and shade treatments in year 1; however visual quality declined greatly for turf under reduced light irradiances and higher N rates by year 2. Rough bluegrass clipping yield and chlorophyll content generally increased linearly with increasing N rates; while shade increased clipping yield by 28% in December 2006 and reduced yield by 38 and 33% in December and February 2007, respectively. Leaf tissue N concentrations were greatest under the highest N rates until February of year 2 when the 98 kg K ha-1 yr-1 rate produced 16% greater tissue N concentration compared to the 147 kg K ha-1 yr-1 rate. Rough bluegrass treated with foliar applications of Fe generally exhibited minimal and inconsistent effects on leaf N, Fe and chlorophyll content compared to non-Fe treated turf.

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