and sulphur-coated urea were evaluated from 1991 to 1993 on a creeping bentgrass (Agrostis palustris) green and a Kentucky bluegrass (Poa pratensis) lawn for their effects on soil bacterial and fungal populations and dollar spot disease incidence. Over the 3 yr, fertilizers were applied every 4 wk at recommended rates from early June to September, and once again in November. Application of Ringer fertilizers, ammonium nitrate and sulfur-coated urea gave rise to significantly higher microbial populations on turfgrass leaves and in thatch and soil than most other fertilizers. In most experiments, Ringer fertilizers also improved water retention in thatch compared to other treatments. Ringer Greens Super®, Ringer Turf Restore®, or ammonium nitrate on the creeping bentgrass green significantly suppressed dollar spot disease compared to the other amendments or the untreated control, but for most of the season, they did not control disease as well as the fungicide chlorothalonil. Nitrate leaching from inorganic nitrogen fertilizers has the potential to be a significant source of nitrate contamination of ground water in urban areas where turfgrass is the major living ground cover (17). Frequent application of inorganic fertilizers such as ammonium nitrate can change the soil pH and consequently may alter soil microbial populations and affect plant growth (19, 20, 22). Concerns regarding environmental quality are prompting the development and use of various kinds of organic amendments or fertilizers to reduce or replace inorganic fertilizer and synthetic pesticide use. Organic amendments have been reported to suppress soilborne plant pathogens (6, 15). Recently developed organic turf amendments, such as Ringer Lawn Restore®, Ringer Greens Super® and Ringer Turf Restore® are derived from hydrolysed poultry feather meal, blood meal, wheat germ, potassium sulfate and bone meal. These products contain microorganisms that may be very important in the biological control of diseases caused by species of Phytophthora, Pythium, Rhizoctonia, and Sclerotium (18). They may also directly or indirectly affect the decomposition of thatch and nutrient transformations in soil. Turfgrass thatch is a complex of dead and living roots, stems and organic debris (2). Excessive thatch accumulation can be detrimental to turf quality and is normally controlled through verticutting and top-dressing (2). High microbial activity is important to thatch decomposition and nutrient recycling in turf (3). Cole and Turgeon (5) reported that 1 g of dry soil or thatch from turf of Kentucky bluegrass (Poa pratensis L.) can contain up to 2.8 x 10 8 bacteria and up to 2.8 x 10 6 fungi. Berndt et al. (3) found that application of a range of organic amendments reduced thatch thickness of Kentucky bluegrass, whereas Mancino et al. (11) found that addition of organic amendments increased thatch thickness and soil fungal counts. Soil bacteria and fungi can increase the availability of plant nutrients in soil, form symbiotic associations with turfgrass roots, produc...

Nitrate (NO3−) can leach from golf greens, potentially causing the degradation of surface and ground water quality. A greenhouse experiment was conducted with 11 annual bluegrass (Poa annua var. reptans Hausskn.) ecotypes from eastern Canada (Quebec and Ontario) and the USA, and three bentgrass (Agrostis spp.) species to compare N uptake and potential for N leaching. Two‐month‐old grasses were established for a 6‐wk period in lysimeter columns simulating a golf‐green profile. An unplanted root zone control was included. Water‐soluble fertilizer was applied at 25 kg N ha−1 (NH4NO3) every 14 d for 57 d. Leachate samples were collected every second day and analyzed for NO3–N and ammonium N (NH4–N) content. Dry weight and N concentration were determined on clippings, shoots, and roots. Ammonium N leaching was negligible for all grasses. Less NO3–N leaching losses occurred under bentgrasses (6–11% of applied N) than under annual bluegrasses (28–71% of applied N). Differences in NO3–N leaching were also found within annual bluegrasses; Quebec P. annua > Ontario P. annua > USA P. annua Grasses with a greater aboveground biomass developed a larger and deeper root system and were associated with a greater N uptake (r = 0.94) and, therefore, a lower NO3–N leaching (r = −0.94). Breeding programs and management practices to improve turfgrass root development appear to be critical to reduce fertilizer N leaching under sand‐based putting greens.

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Under pot culture and field conditions, ethephon at rates up to 8 kg ha-t was more injurious to annual bluegrass than to Penncross creeping bentgrass. Ethephon significantly decreased the quality, spreading ability and shoot weight of annual bluegrass, whereas sward quality of the creeping bentgrass grown in pot culture was increased, spreading ability was unaffected and shoot dry weight decreased. Increasing the number of applications at all concentrations increased injury to annual bluegrass and a single application at I kg ha ' reduced annual bluegrass seedhead production. Mots cl6s: Poa annua, Agrostis palustris,6th6phon, qualit6 du gazon

Nitrate (NO3−) leached from golf greens has the potential to impair water quality. Dissolved organic N (DON) is also increasingly recognized as a form leached from fertilized soils. A controlled experiment was conducted to determine (i) the significance of DON in total N leaching losses under simulated golf‐green profiles and (ii) the short‐term contribution of fertilizer to leaching of inorganic and organic N forms. Various turfgrasses were grown in lysimeter columns designed to simulate a golf‐green profile. Fertilizer was applied at 25 kg N ha−1 every 14 d for 55 d, and the last application was labeled with 15N. Leachates were analyzed for NO3−‐N, NH4+‐N, and DON. The 15N recovery was assessed in plant, soil, and leachates. In the presence of plants, 10 to 70% (average 40%) of total N leached was accounted for by DON. Application of 15N revealed that one‐half to two‐thirds of NO3−‐N leached in the following 14 d was derived from the fertilizer, whereas the majority of leached DON was derived from soil residual N. Nevertheless, DO15N was present in most leachate samples collected for 14 d after fertilizer application, indicating that only a few days were required to convert mineral fertilizer to leachable organic forms. We conclude that DON may be a significant component of total N leaching losses from putting greens and would account for part of the N losses traditionally attributed to volatilization and denitrification.