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Y.L. Qian and J.D. Fry

Textbook recommendations suggest that turf should be watered deeply and infrequently to encourage drought resistance. Data supporting this recommendation are lacking, however. Studies were done to determine the influence of irrigation frequency on `Meyer' zoysiagrass (Zoysia japonica Steud.) rooting and drought resistance. Turf was established on a silt loam soil in 27-cm-diameter by 92-cm-deep containers in the greenhouse. Irrigation was performed daily or at the onset of wilt with a water volume equal to daily or cumulative evapotranspiration of well-watered turf in small weighing lysimeters. After 90 days of irrigation treatments, a dry-down was imposed during which no additional water was applied for >50 days. Compared to turf irrigated daily, turf watered at the onset of wilt exhibited: i) lower (more-negative) leaf water and osmotic potentials prior to the onset of drought; ii) higher leaf water potential and better turf quality at the end of dry-down; and iii) deeper rooting as indicated by lower soil moisture content at 50- and 70-cm depths at the end of dry down.

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Y.L. Qian and J.D. Fry

`Meyer' zoysiagrass (Zoysia japonica Steud.) was established on a silt loam soil in 27-cm-diameter × 92-cm-deep containers in a greenhouse to investigate the influence of irrigation frequency on turfgrass rooting and drought tolerance. Turf was irrigated daily or at the onset of leaf rolling with a water volume equal to the cumulative evapotranspiration of well-watered turf in small weighing lysimeters. After >90 days of irrigation treatments, a dry-down was imposed during which no additional water was applied for 55 days. A recovery period followed during which time turf was watered to maintain soil matric potential at greater than –30 kPa. Compared to turf irrigated daily, that watered at the onset of leaf rolling exhibited 1) 32% to 36% lower leaf water potential and 14% to 22% lower osmotic potential before the onset of drought; 2) 13% higher leaf water potential ≈40 days into dry-down; 3) more extensive rooting at 55- and 75-cm soil depths as indicated by 11% to 19% lower volumetric soil moisture content at the end of dry-down; 4) 25% to 40% lower shoot growth rate during irrigation and 13% to 33% higher shoot growth rate during dry-down; and 5) higher quality ratings during dry-down and recovery. Thus, deep, infrequent irrigation better prepares zoysiagrass for an oncoming drought than light, frequent irrigation.

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Y.L. Qian and J.M. Fu

Salt problems in turfgrass sites are becoming more common. The effects of mowing height on salinity tolerance and associated mechanisms are not well understood. The objective of this study was to examine the effects of mowing height and the level of salinity on turf quality, canopy photosynthetic rate (Pn), total nonstructure carbohydrate (TNC) content, shoot reducing sugar content (RSC), Na+ and K+ content in shoots and roots of creeping bentgrass (Agrostis palustris Huds.). Sod pieces of `L-93' were grown in a greenhouse for over 7 months. Plants were subjected to three mowing heights: 6.4, 12.7, and 25.4 mm, and to four salinity levels of irrigation water: control, 5 dS·m–1, 10 dS·m–1, and 15 dS·m–1 prepared using ocean salts. Increasing salinity resulted in reduced turf quality, increased shoot Na+, reduced K+, and reduced K to Na ratio, to a greater extent for bentgrass mowed at 6.4 mm mowing height. Reducing sugar content in shoot increased with increasing salinity level except at 15 dS·m–1 and 6.4 mm mowing regime where RSC declined. Compared to the 25.4 mm mowing height, mowing height at 6.4 mm caused 32-39% reduction in TNC, a 25% to 37% increase in Na+ content, and 45% to 51% decrease in K content in shoots, which resulted in substantial decrease in K/Na ratio. These results demonstrated that the reduction of creeping bentgrass salt tolerance under low mowing height was associated with carbohydrate depletion that reduced the plant's genetic abilities to generate osmo-protectants (such as reducing sugar), to reduce Na+ accumulation in shoots, and to selectively uptake and transport K+. Therefore, a moderate increase in mowing height could improve salinity tolerance of creeping bentgrass.

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Z.G. Tan and Y.L. Qian

Turfgrasses grown under low light conditions generally exhibit increased shoot elongation. Gibberellic acids (GAs), GA1 in particular, promote stem elongation in grass species. GA20 is the immediate precursor of GA1. However, a direct quantitative measurement of GA1 and GA20 has not been reported for turfgrass under different light intensities. This study was conducted in a greenhouse to quantify the endogenous levels of GA1 and GA20 of `KenblueTimes', `Livingston', and `NuGlade' Kentucky bluegrass (Poa pratensis L.) under two light intensities with and without trinexapacethyl (TE) application. GA1 and GA20 content in leaf tissue were analyzed using gas chromatography-mass spectrometry with deuterium-labeled GA1 and GA20 as internal standards. Light reduction of 73% under greenhouse conditions increased GA1 by 44% to 47% and GA20 by 16% to 50%. `NuGlade' had a GA1 content 20% lower than that of `Kenblue', suggesting that the dwarf characteristics of `NuGlade' may be related to its low GA1 content. The application of TE (0.1 kg·ha-1) reduced GA1 concentration by 47%, but increased GA20 concentration by 146%, supporting the contention that TE inhibited GA1 biosynthesis by blocking the conversion of GA20 to GA1. Chemical names used: 4-(cyclopropyl- -hydroxy-methylene)-3,5-dioxo-cyclohexanecarboxylic acid ethyl ester (trinexapac-ethyl); gibberellic acid (GA).

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Y.L. Qian and M.C. Engelke

Determining the appropriate level of irrigation for turfgrasses is vital to the health of the turfgrass and the conservation of water. The linear gradient irrigation system (LGIS) allows long-term assessment of turf performance under continuous irrigation gradients from excess to no irrigation. The objectives of this study were to: 1) evaluate the minimum irrigation requirements and relative drought resistance of `Rebel II' tall fescue (Festuca arundinacea Schreb.), `Meyer' zoysiagrass (Zoysia japonica Steud.), `Tifway' bermudagrass [Cynodon dactylon (L.) Pers.], `Prairie' buffalograss [Buchloe dactyloides (Nutt.) Engelm], and `Nortam' St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze]; and 2) evaluate the long-term effects of irrigation levels on turf persistence, weed invasion, and disease incidence for the five selected turfgrasses under field conditions. Turf was sodded under LGIS with an irrigation gradient ranging from 120% Class A pan evaporation (Ep) to natural precipitation, along a 20-m turf area. Evaluation during the summers of 1993–96 indicated that grasses differed in drought resistance and persistence under variable irrigation regimes. Irrigation (Ep) required to maintain acceptable turf quality for respective grasses was `Rebel II' (67%), `Meyer' (68%), `Nortam' (44%), `Tifway' (35%), and `Prairie' (26%). Higher dollar spot (Sclerotinia homoeocarpa Bennett) infection was observed at 115% Ep irrigation regime in `Tifway' bermudagrass, whereas gray leaf spot [Pyricularia grisea (Hebert) Barr] was observed only at 10% Ep irrigation regime in St. Augustinegrass plots. An outbreak of brown patch (Rhizoctonia solani Kuehn.) occurred in Sept. 1996 in St. Augustinegrass plots receiving irrigation at >80% Ep.

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S. Ball, Y.L. Qian, and C. Stushnoff

No information is available regarding endogenous soluble carbohydrate accumulation in buffalograss [Buchloe dactyloides (Nutt.) Engelm.] during cold acclimation. The objective of this study was to determine composition of soluble carbohydrates and their relationship to freezing tolerance in two buffalograss cultivars, 609 and NE 91-118, with different freezing tolerances. The experiment was conducted under natural cold acclimation conditions in two consecutive years in Fort Collins, Colo. Based upon average LT50 (subfreezing temperature resulting in 50% mortality) from seven sampling intervals in 1998-99 and six sampling intervals in 1999-2000, `NE 91-118' survived 4.5 °C and 4.9 °C colder temperatures than `609', during the 1998-1999 and 1999-2000 winter seasons, respectively. Glucose, fructose, sucrose, and raffinose were found in both cultivars in both years, and were generally higher in acclimated than pre- and post-acclimated stolons. Stachyose was not present in sufficient quantities for quantification. Cultivar NE 91-118 contained 63% to 77% more glucose and 41% to 51% more raffinose than `609' in the 1998-99 and 1999-2000 winter seasons, respectively. In 1999-2000, fructose content in `NE 91-118' was significantly higher than that of `609'. A significant negative correlation was found between LT50 vs. all carbohydrates in 1999-2000, and LT50 vs. sucrose and raffinose in 1998-99. Results suggest that soluble carbohydrates are important in freezing tolerance of buffalograss.

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Y.L. Qian, A.J. Koski, and R. Welton

Understanding the possible influence of inorganic soil amendments on salt leaching and deposition is helpful in selecting soil amendments when salinity is a problem. Greenhouse experiments were conducted to: 1) evaluate the effects of isolite and zeolite on turf quality of Kentucky bluegrass (Poa pratensis L.) under three salinity levels; and 2) determine if soil amendments affected leachate composition, salt deposition, and soil sodium absorption ratio (SAR). `Challenger' Kentucky bluegrass was grown in columns filled with 100% sand, 50 sand: 50 isolite, and 50 sand: 50 zeolite (v/v). Irrigation waters with three levels of salinity [0.25 (control), 3.5, or 6.5 dS·m-1] were applied daily for 3 months in Study I and for 6 months in Study II. Saline water reduced turf quality compared with control. Amendment of sand with isolite increased turf quality only during the third month of treatment with the most saline water in Study I. However, zeolite increased turf quality during both the second and third months at both salinity levels in both studies. The beneficial effects of zeolite on turf quality diminished 5 and 6 months after salinity treatments. Amending sand with zeolite reduced leaching of Na+ and K+, but increased the leaching of Ca2+ and Mg2+. Amending sand with zeolite increased SAR values by 0.9, 1.6, and 6.3 units in Study I and 0.9, 3.6, and 10.9 units in Study II, under control, 3.5, and 6.5 dS·m-1 salinity treatments, respectively. Isolite increased SAR by 1.1-1.6 units with 3.5 dS·m-1 and by 2.5-3.5 units with 6.5 dS·m-1 salinity treatments. Results indicate that amending with zeolite may buffer soil solution Na+ concentration in the short-term. In the long-term, however, a substantial amount of Na+ may be retained concurrent with Ca2+ and Mg2+ exchange, thereby increasing sodicity and salinity problems.

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J.M. Fu, A.J. Koski, and Y.L. Qian

Salt problems in turfgrass sites are becoming more common. The effects of mowing management on salinity tolerance are not well understood. The objective of this study was to examine the effects of three mowing regimes on turf quality and growth responses of `L-93' creeping bentgrass (Agrostis palustris L.) to salinity stress. Sods of `L-93' creeping bentgrass were grown in containers (45 cm long and 10 cm in diameter) in a greenhouse. Treatments included three mowing regimes (clipping three times weekly at 25.4 mm, four times at 12.7 mm, and daily at 6.4 mm) and four levels of irrigation water salinity (control, 5, 10, and 15 dS·m-1). The relationship of increasing soil salinity with increasing irrigation water salinity was linear in each soil layer. Increasing salinity reduced turf quality and clipping yield more severely and rapidly when mowed at 6.4 mm than at 12.7 or 25.4 mm. Regression analysis of soil salinity and turf quality suggested that turf quality of creeping bentgrass mowed to 6.4, 12.7, and 25.4 mm fell to an unacceptable level when soil salinity reached 4.1, 12.5, and 13.9 dS·m-1, respectively. Data on turf quality, clipping yield, and verdure indicated that salinity damage becomes more severe under close mowing conditions and that a moderate increase in mowing height could improve salinity tolerance of creeping bentgrass.

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Saad Alshammary, Y.L. Qian, and S.J. Wallner

The need for salinity-tolerant turfgrasses is increasing because of increased use of effluent water for turfgrass irrigation. Greenhouse studies were conducted to determine the relative salt tolerance and salt tolerance mechanisms of `Challenger' Kentucky bluegrass (Poa pratensis), `Arid' tall fescue (Festuca arundinacea), `Fults' alkaligrass (Puccinellia distans.), and a saltgrass (Distichlis spicata) collection. Kentucky bluegrass and tall fescue were irrigated with saline solutions at 0.2,1.7, 4.8, or 9.9 dS/m, whereas alkaligrass and saltgrass were irrigated with saline solutions at 0.2, 28.1, 32.8, or 37.5 dS/m prepared using a mixture of NaCl and CaCl2. The salinity levels that caused 50% shoot growth reduction were 9.0, 10.4, 20.0, and 28.5 dS/m for Kentucky bluegrass, tall fescue, saltgrass, and alkaligrass, respectively. Concentrations of proline, a proposed cytoplasmic compatible solute, were 25.8, 30.4, 68.1, and 17.7 μmol/g shoot fw in Kentucky bluegrass, tall Fescue, alkaligrass, and saltgrass, respectively, at the highest salinity level imposed. Bicellular, salt-secreting glands were only observed by scanning electron microscopy on leaves of saltgrass, indicating salt secretion is one of the important salt tolerance mechanisms adopted by saltgrass. Ion contents (Na, Cl, and Ca) in both shoots and roots of all grasses increased with increasing salinity levels. However, alkaligrass maintained a much lower Na, Ca, and Cl contents in roots and shoots than other grasses, suggesting that ion exclusion is one of the major salt tolerance mechanisms in alkaligrass. Tall fescue did not appear to restrict the uptake and translocation of salt in shoot tissues, but maintained a higher K/Na ratio than all other grasses under saline conditions.

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J.D. Fry, P.H. Dernoeden, W.S. Upham, and Y.L. Qian

Field studies were conducted in Kansas and Maryland to compare the safety and efficacy of halosulfuron-methyl (HM) and bentazon for topkill of yellow nutsedge (Cyperus esculentus L.). Kentucky bluegrass (Poa pratensis L.) and creeping bentgrass (Agrostis palustris Huds.) treated with single (in Kansas) or sequential (in Maryland) HM (35 to 140 g·ha–1) or bentazon (1120 or 1680 g·ha–1) applications exhibited little injury, and treated turf had acceptable quality in all studies. Bentazon caused an unacceptable reduction in perennial ryegrass (Lolium perenne L.) quality at ≥5 weeks after treatment in four of five tests. Perennial ryegrass quality declined linearly with increasing HM rates (between 35 and 140 g·ha–1). In Maryland, HM (≥70 g·ha–1) elicited unacceptable perennial ryegrass quality for 2 or 3 weeks; however, in Kansas, quality was unacceptable for ≈1 week. In Kansas, yellow nutsedge topkill by HM (70 kg·ha–1) ranged from 52% to 97%. A single HM application (35, 70, or 140 kg·ha–1) provided > 97% topkill in Maryland. Yellow nutsedge topkill by bentazon (1680 g·ha–1) generally was inferior to that by HM (70 g·ha–1). Chemical names used: 3-(1-methylethyl)-1H-2,1,3-benzothiadiazin-4 (3H)-one 2,2-dioxide (bentazon), methyl 3-chloro-5-(4,6-dimethoxypyrimidin-2-ylcarbamoylsulfamoyl)-1-methylpyrazole-4-carboxylate (halosulfuron-methyl).