Arizona's golf and sod industry generates $280 M year-1 in revenue and surpasses the vegetable, cotton and dairy industries. Despite the economic worth of turf, a need still exists to conserve the limited supply of potable water in this harsh Sonoran Desert environment. Mandatory water conservation programs have been developed for many sectors of the Arizona economy. To meet this challenge, the turfgrass industry and government bodies have begun to contribute to the development of research programs which reduce turfgrass water requirements and dependence upon potable water. Current research includes a) determining the minimum water requirements of higher quality turf under conditions of high temperatures and vapor pressure deficits; b) the turfgrass potential of grasses with lower water requirements than bermudagrass; c) the development of a statewide weather station network to predict daily turfgrass water use; and d) determine management strategies for turfgrass irrigated with wastewater effluent. The overall goal of these programs is to produce high quality and functional turf with 20 to 50 percent less water.
Many biotypes of annual bluegrass (Poa annua L.) are found on golf course putting greens. Although normally considered an invasive weed, annual bluegrass can provide as good a putting surface as creeping bentgrass (Agrostis palustris Huds.). The most desirable biotypes of annual bluegrass are primarily vegetative and have a low flowering frequency. Whether the nutritional requirements of annual bluegrass biotypes differ from one another or from creeping bentgrass is unknown. The response of three flowering (FAB, high seedhead production) and three vegetative (VAB, low seedhead production) biotypes of annual bluegrass (AB), and the three parents of `Penncross' creeping bentgrass (CB) to varying levels of iron (Fe) in greenhouse sand culture was investigated. After establishment, clones were grown for 3 weeks and irrigated with a half-strength Hoagland's solution containing 0, 2, 4, 6, and 8 mg·L-1 Fe in citrate-Fe. Shoot and root responses to Fe were similar for the VAB and FAB biotypes. However, VAB had higher color ratings (darker green leaf color) with Fe treatment level at 4 mg·L-1 than did FAB or CB, which required 6 mg·L-1 Fe for acceptable color. Growth of creeping bentgrass was greater than that of annual bluegrass at every Fe level tested. Shoot dry weights of CB increased significantly with Fe treatment level up to 6 mg·L-1. Shoot dry weight of AB increased up to 4 mg·L-1 Fe and then declined at ≥6 mg·L-1. Root growth of CB increased up to 6 mg·L-1 Fe, but then decreased significantly at 8 mg·L-1 Fe. Root growth of AB increased slightly up to 4 mg·L-1 Fe and then declined at 6 and 8 mg·L-1. Shoot tissue concentrations of Fe were similar for AB and CB at each Fe rate tested except at 8 mg·L-1 Fe, where Fe levels in CB were significantly lower. Based on this work, creeping bentgrass and annual bluegrass respond differently to Fe nutrition, but different biotypes of annual bluegrass appear to respond similarly.
Annual bluegrass (Poa annua L.) is becoming an important component of golf course putting greens. A greenhouse sand culture experiment was conducted to study the zinc (Zn) requirements of three genotypes of flowering annual bluegrass (FAB) and three genotypes of vegetative annual bluegrass (VAB), which were compared with the three parents of `Penncross' creeping bentgrass [Agrostis stolonifera L. (CB)]. Clonally propagated plants were grown in sand culture without Zn for 6 weeks prior to the initiation of the Zn treatments. The plants were then irrigated for 3 weeks with half-strength Hoagland's nutrient solution containing 0, 2.5, 5.0, or 40 mg·L-1 Zn from ZnSO4. Color was the only parameter affected by genotype; each genotype showed a significant quadratic response to increasing levels of Zn, with highest color ratings occurring at 2.5 mg·L-1. No genotypic differences were observed among CB, VAB, and FAB for shoot fresh and dry weight, root dry weight, or shoot tissue Zn concentrations. Shoot dry weight of all genotypes increased quadratically with Zn levels. Root dry weights of both VAB and FAB increased, while that of CB remained unchanged, as Zn level increased. Zinc concentrations in shoot tissue increased linearly as Zn level increased. Shoot Zn concentrations were higher in both VAB and FAB than in CB at each Zn level, but differences between VAB and FAB were insignificant. Maintaining shoot Zn concentrations below 109 mg·kg-1 in CB and 200 mg·kg-1 in VAB or FAB prevented Zn phytotoxicity from occurring.
This study was conducted to determine: 1) if the Minolta CR-310 Chroma Meter can detect color differences among bentgrass (Agrostis stolonifera L., A. capillaris L.) cultivars maintained as a turf; 2) how the CR-310 parameters of hue angle, lightness, and chroma compare with visual color assessments; and 3) if the CR-310 can provide consistent color measurements among evaluators. Differences were detected among cultivars with respect to hue angle, lightness, and chroma. Hue angle and chroma were significantly correlated with visual color assessments when data were averaged across all evaluators. Lightness was not strongly associated with visual color assessment. Differences were found among evaluators for visual color assessment, lightness, and chroma, but not for hue angle measurements. Thus, hue angle appears to be the most consistent CR-310 parameter for measuring color of bentgrass turf. These results indicate that the CR-310 can be used to evaluate the color of bentgrass cultivars maintained as a turf and provides consistent hue angle measurements among evaluators, regardless of experience in rating turf color. The CR-310 is probably best used for measuring relative color differences and may be useful if cultivars of similar color are desired in blended turfs.
Combining frequent N applications and irrigations for turfgrasses grown in sandy soils is a common occurrence on golf course putting greens. A greenhouse study was conducted to determine leaching losses of nitrate and ammonium nitrogen from `Penncross' creeping bentgrass (Agrostis palustris L.) growing on an 80 sand:20 peat soil mixture following frequent, moderately heavy irrigations and light or moderate N fertilizer applications. Nitrogen sources included calcium nitrate, ammonium nitrate, ammonium sulfate, urea, urea formaldehyde and isobutylediene diurea. Application levels were 9.76 kg N/ha per 7 days and 19.52 kg N/ha per 14 days for 10 weeks. Irrigation equivalent to 38 mm·week-1 was applied in three equal applications. Overall, 46% of the applied water leached. Total leaching losses were <0.5% of the applied N. Nitrate represented the major portion of the leached N, with ammonium losses being negligible. There were no differences between sources when applied at these levels. In a second study, a single 48.8 kg N/ha application resulted in higher leaching losses of N, but only calcium nitrate and ammonium nitrate had total losses > 2% (2.80% and 4.13%, respectively, over an n-day period). Nitrate concentrations were found to exceed 45 mg·liter-1 for ammonium nitrate.
The loss of fertilizer granules collected in turf clippings during routine putting green mowing has not been determined. The objective of this study was to quantify the amounts of greens-grade granular potassium (K) and nitrogen (N) fertilizers collected during the routine mowing of a `Pennlinks' creeping bentgrass (Agrostis palustris Huds.) putting green. In the first study, five K-containing granular fertilizers were applied at K rates of 2.43 and 4.86 g·m-2. A second study was also performed with six granular Ncontaining fertilizers and one liquid N fertilizer applied at an N rate of 4.86 g·m-2. Both studies were performed twice. Irrigation (6.4 mm) was applied immediately after each fertilizer application and again on the following day. These two irrigations, plus additional irrigation and rain, resulted in each study receiving about 2.54 cm of water over each nineday study period. Mowing and clipping collection using a walk-behind greens mower set to cut at 3.96 mm began two days after treatment (2 DAT) and continued until 9 DAT. The clippings were oven-dried and separated from the fertilizer using a small pneumatic seed cleaner. Collected fertilizer was weighed and expressed as a percentage of the fertilizer applied. Liquid N fertilizer loss was estimated to be the difference between clipping N content of treated plots and untreated controls. Total K fertilizer loss was: UHS Signature 15-0-30 (15.3% to 22.9%) > Lebanon Isotek 11-3-22 (8.7% to 10.7%) > Scott's Contec 13-2-26 (4.9% to 7.4%) > Lesco Matrix 12-0-22 (0.1% to 0.4%) = Lesco Matrix 5-0-28 (0.1% to 0.5%). Signature was the only fertilizer significantly affected by rate and a greater percentage of loss occurred at the lower K application rate. Most loss occurred during the first and second mowing events with small amounts of fertilizer found in clippings from later mowings. The two Lesco materials were not found in clippings after the first mowing. Nitrogen fertilizer granule loss was also greatest with the first and second mowings. Total percentage of losses were IBDU 31-0-0 (75.4%) > Polyon 41-0-0 (70.8%)> Milorganite 6-2-0 (55.7%) > Nutralene 40-0-0 (47.0%) > UHS Signature (19.3%) > Isotek 11-3-22 (9.5%) > N-Sure Pro 30-0-0 (1.9%). In both studies, fertilizer loss appeared to be most related to water-solubility of the fertilizer, but size and density might also be factors.
This study examined the numbers of specific soil and thatch microbial populations in a U.S. Golf Association (USGA) specification sand-peat putting green of creeping bentgrass (Agrostis palustris Huds.) over 17 months. Changes caused by adding a water-soluble or bio-organic (water-insoluble, contains microbial inoculum) N source were examined. Thatch was found to contain 40 to 1600 times as many bacteria as the soil, 500 to 600 times as many fungi, and up to 100 times as many actinomycetes. Soil populations of nitrate- and nitrite-reducing anaerobes were similar and ranged from 103 to 105 per gram of dry soil. Adding the bio-organic N source increased soil fungal counts and thatch thickness when compared with the control (no N applied), but not as much as the water-soluble N source. The amendments had no effect on soil respiration, total organic carbon. or total N content.