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This article in AJ

  1. Vol. 76 No. 1, p. 65-71
    Received: Jan 10, 1983
    Published: Jan, 1984



Effects of Sulfur and Nitrogen Levels and Clipping on Competitive Interference Between Two Annual Grass Species

  1. D. M. Center,
  2. M. B. Jones and
  3. C. E. Vaughn1



Annual ryegrass (Lolium multiflorum Lam.) and soft chess (Bromus mollis L.) are often seeded for increased forage production and erosion control on California annual rangelands. Observations in grazed pastures and small plots indicate that the relative proportions of these two species in the community can be influenced by the application of S and N fertilizers. The purpose of this study was to further define the effects of S, N, and clipping on yield response and interference between these two important annual grassland species. Plants were grown in a greenhouse in unleached pots filled with Josephine loam (fine-loamy, mixed, mesic Typic Haploxerults). Both species were seeded in monoculture and in a 5050 mixture at a total density of 2000 viable seed m−2. Treatments were factorial combinations of 0, 10, 20, 30, 40, or 80 mg S kg−1 soil at the time of planting and N applied at 10 or 30 mg kg−1 soil every 14 days. Onehalf of the pots were clipped to a height of 3 cm every 28 days and the other half were clipped only at the termination of the experiment. Dry matter yield and percent S were measured for all clippings and percent N for the last clipping on the repeatedly clipped pots. Only dry matter production was measured on the pots clipped once at the end of the experiment. Yield and response to S and N of ryegrass was greater than that of brome in all treatments. Yield per plant of ryegrass was greater when grown with brome than in monoculture in both the clipped and unclipped pots. In the clipped pots there was little difference in the yield of brome per plant whether grown in mixture or in monoculture, but under unclipped conditions brome yielded more per plant in monoculture than in mixture. Based on analysis of relative yield totals and relative crowding coefficients no significant competitive interference could be detected in the clipped pots at any S or N level. In the unclipped pots the two species were competing and ryegrass was the better competitor. The nature of the interference was not changed with the addition of S or N. From this it was concluded that at the rates used in this study, the major factor influencing competitive interaction between these two species was light, and S and N levels were not major influencing factors.

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