Tall Fescue Sward Response to Mefluidide and Nitrogen1

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Abstract
Introduction of legumes into grass‐dominant pastures often requires destruction or suppression of existing vegetation to minimize competition for light, soil water, and plant nutrients. Mefluidide (N‐[2,4‐dimethyl‐5‐ [[(trifluoromethyl)sulfonyl]amino]phenyl]acetamide) has been used as a growth retardant of cool‐season turf grasses but has not been evaluated as an aid to legume establishment in pasture renovation. Three field experiments conducted at the Kentucky Agric. Exp. Stn., Lexington, Ky. in 1979 and 1980 examined responses of tall fescue (Festuca arundinacea Schreb.) to mefluidide [0.56 kg (a.i.)ha−1] applied in March and/or May under different levels of fertilization on a Maury silt loam (mixed, montmorillinitic, mesic Typic Paleudult). Mefluidide, applied 2 to 4 weeks after spring growth was initiated, reduced tiller weight, leaf weight/tiller, leaf area/tiller, and tiller populations. Mefluidide had no effect on the rate of leaf appearance and increased leaf/stem ratio from 1.38 to 2.34. Fertilizer N increased tiller populations, leaf dry weights, and leaf area/tiller. March applications of mefluidide reduced canopy leaf area index (LAI), but 65 days later LAI values of these plots were 50% higher than LAI's of untreated plots. Mefluidide application in May reduced LAI more severely than March applications and it did not lead to an increase in LAI later in the season. Application of N tended to offset the reduction of LA1 by mefluidide. Annual dry matter yields of tall fescue were reduced 12, 21, and 40% by March, May, and March plus May applications of mefluidide. Mefluidide broadcast in March reduced dry matter yields harvested on 7 May by 54%, but yield obtained at the next harvest was 23% higher than on untreated plots. Mefluidide applied in May reduced dry matter yields at the next harvest by 60% but subsequent yields were similar to those of untreated plots. At the third harvest on 1 August, dry matter yields of plots receiving 80 kg N haΨ1 were 22, 27, and 49% higher when mefluidide was applied on 29 March, 15 May, or on both dates, respectively. While mefluidide suppressed grass growth for 6 to 8 weeks after application, subsequent stimulation of grass growth may increase competition from grasses. Fertilizer N stimulated grass growth even when treated with mefluidide, and would increase competitiveness of established species.