Understanding the determinants of nitrate leaching should improve nitrogen uptake efficiency and reduce ground water contamination. This column lysimeter study examined the effect of root architecture on NO3 leaching from two genotypes of creeping bentgrass (Agrostis palustris Huds.) differing in rooting characteristics. Ammonium nitrate was applied (50 kg N ha−1) and the columns were irrigated with 1, 2 or 3 cm day−1 (Exp. 1) or irrigation was delayed 1, 3 or 5 d (Exp. 2). In Exp. 1, leachate NO3 concentrations and total N leached from the shallow‐rooted (SR) genotype were approximately twice those from the deep‐rooted (DR) genotype. An average of 38 and 18% of the applied N leached from the SR and DR genotypes, respectively. Cumulative leaching losses increased with irrigation depth. In Exp. 2, NO3 leaching was reduced 90% or more by increasing the time period for immobilization from 1 to 5 d. Recovery of applied 15N in the tissue averaged 87% after 2 mo. Absorption of NO3 and NH4 was measured in nutrient solution culture. The SR genotype had significantly higher uptake rates than DR for both forms of N, expressed on a root weight basis. Collectively these data indicate that a deep‐rooted turfgrass absorbs N more efficiently than a shallowrooted turf, reducing the concentration and total amount of NO3 leached. The effect is apparently not due to differences in N uptake, but rather to rooting patterns. Environmental conditions and management practices that affect rooting depth and density may thus affect N nutrition and NO3 leaching.

‘Diamond’ zoysiagrass [Zoysia matrella (L.) Merr.] has excellent shade tolerance when compared with other zoysiagrass cultivars. However, because of excessive shoot growth and carbohydrate depletion, turf stand declines with time when shade levels exceed 80%. Two separate studies were conducted to determine if the plant growth regulator trinexapac‐ethyl (TE), which suppresses shoot growth, could improve turf performance of Diamond zoysiagrass under shade conditions. Well‐established turf was subjected to a constant 86 and 88% shade in the greenhouse and polyhouse, respectively. Trinexapacethyl treatments included monthly applications at 0.048 kg a.i. ha−1 (MTE), bimonthly applications at 0.096 kg a.i. ha−1 (BTE), trimonthly applications at 0.192 kg a.i. ha−1 (TTE), and the untreated control. Treatments in 1997 were made from January through August for the greenhouse study and from April to September for the polyhouse study. Diamond receiving MTE and BTE maintained acceptable turf quality throughout the study, while turf quality of the control deteriorated to unacceptable levels <3 mo after shading. Diamond treated with TTE maintained better turf quality than that of the control, but was inferior to MTE and BTE treatments. Compared with control plots, turf receiving MTE and BTE had (i) 76 to 73% less shoot vertical growth and 77 to 75% less clippings, (ii) 40 to 38% higher total nonstructural carbohydrate content, (iii) 60 to 50% higher root mass and 51 to 46% higher root viability, and (iv) 48 to 42% higher photosynthesis. Results suggested that monthly or bimonthly repeated application of TE at 0.048 or 0.096 kg a.i. ha−1 greatly enhanced the shade tolerance of Diamond zoysiagrass.

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.

Need for salinity tolerant turfgrasses is increasing because of government mandates requiring use of low quality secondary water sources for turfgrass irrigation. This study was done to elucidate salinity tolerance mechanisms of the Zoysia genus (zoysiagrass), which includes a number of important turfgrasses. Research objectives were to (i) determine the range in salinity tolerance among and within five zoysiagrass species, (it) determine if salt secretion via leaf salt glands is an important salinity tolerance mechanism within the Zoysia genus, and (iii) determine if salinity tolerance is associated with the rate, efficiency of leaf salt gland secretion. Fifty‐seven zoysiagrass accessions and cultivars, representing five interfertile species, were grown in hydroponic tanks in a glasshouse. Salinity of treatment tanks was gradually raised prior to data collection to a final treatment level of 400 mM NaCI. Relative salinity tolerance was determined by changes in percent leaf firing and percent leaf dry weight relative to control plants. Relative percent leaf firing varied from 19 to 80% among entries, indicating a wide range in relative salinity tolerance. Bicellular leaf salt glands were observed in all species, lying recumbent to the leaf surface in parallel rows atop intercostal ridges. Relative salinity tolerance was negatively correlated with leaf sap Na+ concentration and positively correlated with leaf salt gland Na+ secretion rate and leaf gland density. This indicates that salinity tolerance in the Zoysia genus is associated with shoot saline ion exclusion via leaf salt gland secretion, which, in turn, is related to leaf salt gland density.

siagrass genotypes come from diverse origins and are classified as different species. At least five species of Salt tolerant turfgrasses are highly desirable in areas associated zoysiagrass [Zoysia japonica, Z. matrella (L.) Merr., Z. with saline soils and/or saline irrigation waters. To determine the salt tolerance of 29 zoysiagrass (Zoysia spp.) experimental lines and tenuifolia Trin., Z. sinica Hamce, and Z. macrostaycha cultivars, two greenhouse studies were conducted by means of a hy-Franch. & Sav.] and their hybrids have been introduced droponic culture system. Sodium chloride was gradually added to a for turfgrass breeding in the USA. Since all these species basic nutrient solution to obtain a final salinity level of 42.5 dS m Ϫ1 .appear to be sexually compatible and may hybridize, Relative salt injury, indicated by leaf firing percentage, was associatedPublished in Crop Sci. 40: 488-492 (2000).