Effects of year, season, plant species, grazing intensity and nitrogen levels on phytomass variations in grazing grasslands: A use of analysis of variance
2004
Yiruhan. (Jinan Univ., Guangzhou (China)) | Shiyomi, M. | Takahashi, S. | Okubo, T. | Akiyama, T. | Koyama, N. | Tsuiki, M.
Between 1974 and 1989, two 8-year-long grazing experiments were conducted at the National Grassland Research Institute (Nishinasuno, Tochigi, Japan) to determine the effects of grazing intensity and nitrogen levels, respectively, on the pasture ecosystem. Large temporal and spatial variations in phytomass were observed in both experiments. To clarify the cause of the phytomass variations, the present study re-examined the data obtained in these two experiments to determine the effects of four factors and their interactions : Year, Season, Plant species and Treatment (two different grazing intensities or two different nitrogen levels). Although these experiments were not based on any statistical experimental design, we were able to examine these factors using analysis of variance for single-replication experiments. In the analyses. Year was treated as a random effect factor, and Season, Plant species and Treatment were treated as fixed effect factors. The 4-factor interaction was assumed as the experimental error. Based on variance-component values calculated from the analysis of variance, the degrees of contribution of main effects, 2- and 3-factor interactions and error to the whole phytomass variation, were numerically calculated. In these two experiments, the effects of Plant species and 2- and 3-factor interactions containing Plant species made the greatest contributions to the phytomass variations.
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