Chemical Dwarfing and the Response of Cool-Season Grass Seed Crops to Spring-Applied Nitrogen
- William C. Young ,
- David O. Chilcote and
- Harold W. Youngberg
Seed yield response of cool-season grasses to spring-applied N is usually limited because of lodging. This study investigated whether chemical dwarfing of these crops improves their seed yield response to spring-applied N. Chewing's fescue [Festuca rubra L. subsp.fallax (Thuill.) Nyman; syn. F. rubra var. commutata Gaudin], tall fescue (Festuca arundinacea Schreb.), and orchardgrass (Dactylis glomerata L.) were established in September 1983 near Corvallis, OR. Treatments were all combinations of 90,120,150,180, and 210 kg N ha−1 applied at the double-ridge stage of development, followed by paclobutrazol [(2RS,3RS)-l-(4-chlorophenyl)-4,4-dimethyl-2-(1H1,2,4-triazol-l-yl)-pentan-3-ol] at 0, 0.25, 0.5, and 1 kg a.i. ha−1 applied at floret initiation stage in 1985 and 1986. Averaged across years and N rates, the 1 kg ha−1 rate reduced Chewing's fescue height by 23% and tall fescue and orchardgrass heights by 30%. In the absence of paclobutrazol, Chewing's fescue and tall fescue seed yields were the greatest at 90 kg N ha−1. Paclobutrazol did not affect seed yield response of Chewing's fescue to N rates, but tall fescue seed yield in 1986 was the greatest at 150 kg N ha−1 when only 0.25 kg a.i. paclobutrazol ha−1 was applied. Averaged across N rates, the 0.5 kg ha−1 rate increased Chewing's fescue seed yield by 32% in 1985 and 18% in 1986, and also increased tall fescue seed yield by 32% in 1985 and 23% in 1986. Orchardgass seed yield was the greatest at 180 kg N ha−1 in both years. Paclobutrazol did not affect orchardgrass seed yield in 1985, and the 1 kg ha−1 rate decreased seed yield in 1986. We concluded that in western Oregon paclobutrazol application at floret initiation does not improve seed yield response of these crops to spring-applied N, but it would significantly improve Chewing's fescue and tall fescue seed yield, regardless of the N rate applied. Results did not indicate any advantage for applying paclobutrazol on orchardgrass seed crop.
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