Preemergence herbicides have been used extensively on turf in recent years to prevent annual weed development. Applications of these herbicides have been suspected of causing reduced turfgrass quality. The purpose of this study was to determine whether repeated use of preemergence herbicides resulted in thatch development and other effects associated with turfgrass deterioration. Six preemergence herbicides were applied annually for 4 years to ‘Kenblue’‐type Kentucky bluegrass (Poa pratensis L.) growing on an Aquic Argiudoll (Flanagan silt loam). Calcium arsenate and bandane (polychlorodicyclopentadiene) applications were associated with increased leaf spot (Helminthosporium vagans Drechel.) disease, higher wilting tendency, reduced shoot and root growth, and substantial thatch development. The thatching tendency was associated with a complete lack of earthworm (Lumbricus terrestris Linn.) activity in the underlying soil. Bandane residue was largely confined to thatch while calcium arsenate was more generally distributed throughout the upper thatch‐soil profile. Verdure was significantly reduced in plots treated with bensulide [0,0‐diisopropyl phosphorodithioate S‐ester with N‐(2‐mercaptoethyl)benzenesulfonamide] while benefin (N‐butyl‐N‐ethyl‐α,α,α,‐trifluro‐2,6‐dinitro‐p‐toluidine) D C P A (dimethyl tetrachloroterephthalate) and siduron [l‐(2‐methylcyclohexyl)‐3‐phenylurea] treatments, produced no measurable effects.

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Slow-release N fertilizers are used in turfgrass fertilization programs to reduce foliar burn and N losses, and to extend the response period between applications. In this study, oxamide (31% N), an amide of oxalic acid, and a 7:3 N ratio of oxamide and urea were evaluated as slow release N sources on Kentucky bluegrass (Poa pratensis L.) at West Lafayette, IN, on a Toronto silt loam soil (finesilty, mixed mesic, Udollic Ochraqualfs). Two particle sizes of oxamide, C (1-2.8 mm) and F ( <0.85 mm), were applied as a granular and liquid suspension treatment, respectively. Additional treatments consisted of applying isobutylidene diurea (IBDU), sulfur-coated urea (SCU), and urea. Two and four applications were made, with a total annual application rate of 196 kg N ha~• yr~•. Recovery of N in the tissue from applications of oxamide C was 51% compared to 41, 39, and 38% for IBDU, oxamide F, and SCU, respectively, averaged over 3 yr. Initial change in visual turf quality and clipping yields in response to oxamide C was slow, similar to that of IBDU; however, residual N release was equal to that of IBDU and greater than that of SCU. Adding urea to oxamide C increased initial yields and turf quality but reduced the duration of turf response as compared to applications of oxamide C alone. At two applications of 98 kg N ha~ 1 , oxamide proved to be a good, slow-release source of N. At four applications per year, initial clipping yields resulting from spring oxamide F applications were lower than those from urea, but turf quality in response to residual N tended to be greater than that of urea. Late fall applications of oxamide F reduced soil N03 concentrations shortly after application and in early spring as compared to fall applications of urea. Oxamide F at four applications generally produced a more desirable turf response than did similar applications of urea.Additional index words: Isobutylidene diurea, Sulfur-coated urea, Nitrogen recovery, Soil inorganic nitrogen, Poa pratensis L. Agron. J. 79:720-725 (1987). Published in

Dicyandiamide (DCD), a nitrification inhibitor, is a 67% N compound of low volatility that can be incorporated into fertilizer granules. Urea, ammonium sulfate (AS), and a complete fertilizer (COMP), all amended with DCD so that I 0% of the N was derived from DCD, were evaluated in field studies at West Lafayette, IN, on 'Wabash' Kentucky bluegrass (Poa pratensis L.) grown on Toronto silt loam (fine-silty, mixed, mesic Udollic Ochraqualfs). Urea, AS, sulfur-coated urea (SCU), and isobutylidene diurea (IBDU) were included for comparison. Equal treatments were applied two or four times per season to provide 196 kg N ha-•yr-•. Clipping yields in response to DCDamended fertilizers were similar to those of urea and AS at both N regimes. Initial response to DCD-amended fertilizers was rapid and response to residual N shorter than that of IBDU and SCU; however, recovery of applied N in the tissue was similar between DCD fertilizers and IBDU, and SCU. Averaged over 3-yr, recovery of N ranged from 41.1% for IBDU to 36.4% for AS at 2 X 98 kg N ha-•, and 39.0% for COMP + DCD to 32.6% for AS at 4 X 49 kg N ha-1 , respectively. Turf quality of plots receiving IBDU was superior to all N sources. Measurements 24 days after a 15 November application in 1984 indicated DCD inhibited N0.3 formation at the 2 X 98 kg N ha-• rate (14.6 kg DCD ha-1 ). Fall-applied DCD did not influence soil NHt and N03 concentrations at 0 to 0.20 m the next spring. The short period of effectiveness of DCD would seldom warrant its use as a nitrification inhibitor in turf.Additional index words: Isobutylidene diurea, Sulfur-coated urea, Soil inorganic N, Nitrogen recovery, Poa pratensis L. W ITH the ~ncreasing cost of N fertilizers and the potential for N03 pollution of lakes and groundwater, efficiency inN management is extremely important. Applications of slow-release N tend to minimize leaching losses by reducing concentration of NO) in the soil solution. Bredakis and Steckal (1963) reported N03 release in this order: (NH 4 hS0 4 = urea > sewage sludge > ureaformaldehyde (UF). Residual N was found to be greater with sulfur-coated urea (SCU) applications, however, leaching losses of N03 were less than 11% of a 400 kg N ha-1 application for all soluble and insoluble N sources (Allen et al., 1978). Others have reported higher residual N with SCU than isobutylidene diurea (IBDU); however, split applications of these materials were necessary to produce 1