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The following abstracts were extracted from publications over the past year. They include a number of papers of interest that would not normally be reviewed by turf and landscape professionals.

Treating the Cause, Not the Symptoms. Irrigation water treatment for better infiltration. R. N. Carrow, R. R. Duncan, and M. Huck, USGA Green Section Record. Vol. 37, No. 6, November/December 1999, p. 11-15.

Some constituents found in irrigation water can influence water infiltration into the soil. Whether chemical treatment of the irrigation water is required depends on the specific problem. There are conditions where soil-applied treatments can be equally or more effective. The type of chemical treatment also is dependent on the nature of the problem. Four situations can occur that limit water infiltration into soils:

High Na, Low HCO³/CO³: Irrigation water treatment is not necessary, but amendments to alleviate sodic conditions can be delivered through an irrigation system or they can also be directly applied to the turfgrass. Possible amendments for water treatment include gypsum, soluble Ca materials, or a S-based acid to combine with soil-applied lime to form gypsum.

High to Moderate Na, High H CO³/ CO³: Acidification of the irrigation water to remove excess H CO³ is strongly preferred.

Ultra-Pure Water: Gypsum injection is an option, and other soluble salts could be added to the irrigation water to raise ECW. Or, salts can be directly applied to the soil. If soil application is the chosen method of treatment, a light and frequent approach is suggested to avoid leaching all the amendment beyond the surface and into the soil a few centimeters. This could result in the infiltration problem recurring at the surface.

High Ca/Mg, High H CO³/ CO³: If sufficient calcite forms at the surface to decrease infiltration rates, acidification of the irrigation water is an option. Cultivation, use of acid fertilizers, and direct S application to the turf can produce similar results.

Pros: Water treatment eliminates dust associated with granular soil applications of amendments such as lime, gypsum, or sulfur. This can be an important consideration where strict air quality regulations exist or residential developments surround a golf course.

Water treatment can reduce labor requirements and eliminate course downtime when compared to granular soil applications. Water acidification can reduce the burn potential associated with soil sulfur applications, especially on low-CEC soils such as sands, lava rock, or decomposed granite. Cons: Pound-for-pound of active ingredient, liquid amendments generally cost more than dry products. Equipment for water treatment can be an expensive investment costing from $8,000 to $30,000, depending on the type of equipment and treatment necessary. Where acidification is required, products must be evaluated and selected carefully, as some options are dangerous to handle until diluted in the irrigation water. Application uniformity of water treatments is only as good as the distribution uniformity of the irrigation system.

Lolium perenne grasslands may function as a sink for atmospheric carbon dioxide. van Ginkel, J. H.;; Whitmore, A. P.; Gorissen, A. Journal of Environmental Quality. Vol. 28, No. 5, September/October 1999, p. 1580-1584. Model calculations and scenario studies suggest the existence of a considerable positive feedback between temperature and carbon dioxide (CO²) levels in the atmosphere. Rising temperatures are supposed to increase decomposition of soil organic C leading to an increased production of CO² and this extra CO² induces a positive feedback by raising the temperature still further. Evidence was found that negative feedback mechanisms also exist: more primary production is allocated to roots as atmospheric CO² rises and these roots decompose more slowly than roots grown at ambient CO² levels.

Experimental data partly obtained with 4C-techniques were applied in a grassland carbon (C) model. The model results show that at an atmospheric CO² concentration of 700ML L- increased below ground C storage will be more than sufficient to balance the increased decomposition of soil organic C in a ryegrass (Lolium perenne L.) grassland soil. Once a doubling of the present atmospheric CO² concentration has been reached, C equivalent to 55% of the annual CO² increase above 1 ha ryegrass can be withdrawn from the atmosphere. This indicates that grassland soils represent a significant sink for rising atmospheric CO² .

Temporal shade on creeping bentgrass turf. Bell, G. E.; Danneberger, T. K. Crop Science. Vol. 39, No. 4, July/August 1999, p. 1142-1146.

Creeping bentgrass (Agrostis palustris Huds.) turf exposed to shade during morning hours may decline more readily than similar turf exposed to afternoon shade. This study compared the quality and physiological responses of creeping bentgrass turf exposed to morning shade with turf exposed to afternoon shade and evaluated responses of the same species exposed to varying shade densities during the same period. Semipermanent shade structures were placed on a creeping bentgrass range maintained at a 6.4-mm height. Structures provided 6 h of morning shade or 6 h of afternoon shade during the summer solstice. Each structure was covered with either 80 or 100% shade cloth and replicated three times. Control treatments of full sun and perpetual shade were also included. Treated turf was evaluated monthly for color, density, root mass, pigment concentrations, and total nonstructural carbohydrates (TNC). Regardless of response tested, no significant variation was found between plots receiving morning shade and afternoon shade or between plots in 80 and 100% shade. Canopy temperature, in comparison with air temperature, was 7% greater in morning shade than in afternoon shade, but the relationship between canopy temperatures in full sun and shade did not change during the day. Perpetual shade caused a 38% decrease in color and a 33% decline in density but treatments receiving 6 h of shade did not vary from the full sun treatment. Concentrations of chlorophyll a (46%) and b (50%), neoxanthin (31%), violaxanthin (44%), and lutein (34%) declined in perpetual shade compared with full sun. Violaxanthin concentration was influenced by photosynthetic photon flux, suggesting its potential use as a shade stress indicator.

Growth responses and performance of Kentucky bluegrass under summer stress. Bonos, Stacy A.; Murphy, James A. Crop Science. Vol. 39, No. 3, May/June 1999, p. 770-774.

Cultivars and selections of Kentucky bluegrass (Poa pratensis L.) exhibit varying degrees of summer stress tolerance. Understanding the factors associated with performance under summer stress is important for identifying stress tolerant germplasm. The objective of this field study was to evaluate shoot and root growth responses of 10 Kentucky bluegrass genotypes subjectedto high temperature and drought stress conditions in New Jersey. Turf canopy characteristics, shoot and root growth responses, and soil water depletion patterns were evaluated on a Nixon Loam (fine-loamy, mixed mesic TypicHapludult) and used to characterize Kentucky bluegrass selections having variable summer stress tolerance. Tolerant entries maintained 19% more roots at the 15- to 30-cm depth in 1995 and 65% more roots at the 30- to 45-cm depth than intolerant entries. Gravimetric soil water contents of tolerant plants were significantly lower at the 15- to 30-cm depth than intolerant entries for both years. Tolerant Kentucky bluegrass, able to exploit deep soil moisture under heat and drought conditions, exhibited significantly fewer summer stress symptoms, had significantly lower stomatal resistance (based on subset of cultivars), and maintained canopy temperature 5 degrees C cooler than intolerant entries at the end of stress periods. This indicated that maintenance of transpirational cooling was an important factor associated with better summer stress performance of turf plots under high termperature and drought conditions in New Jersey.

Reprinted courtesy of the GTI Advisor, Vol. 5, No. 1, January 4, 2000

The GTI Advisor is published by the Guelph Turfgrass Institute,
University of Guelph, Guelph, Ontario Canada N1G 2W1
Telephone (519) 767-5009 Fax (519) 766-1704
Editor: Rob Witherspoon
© 2000, Guelph Turfgrass Institute

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Turf Line News June/July 2000

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