Abstract:

The competition relationships among perennial ryegrass (Lolium perenne) and six other species (Trifolium repens, Dactylis glomerata, Imperata cylindrical, Miscanthus sinensis, Spiraea japonica var. nepalensis, and Sanguisorba officinalis) were studied in different conditions of stress and disturbance. The aim was to examine the mechanism of regressive succession of ryegrass community, in order to supply a basis for efficient management of this pasture.Two stress factors (water condition and soil fertility) and two disturbance factors (cutting frequency and cutting intensity) were included in the experiment. The water condition treatment included two levels, which were natural precipitation (about 1 800 mm) and precipitation + watering (about 2 300 mm). The soil fertility treatment included three levels at which fertilizer was applied: 0 kg·hm-2·a-1, 75 kg·hm-2·a-1 and 150 kg·hm-2·a-1. The cutting frequency treatment included three levels at which plants were cut: 1, 3 and 6 times per year. The cutting intensity treatment included two levels of stubble height, 2 cm and 3 cm. The plants were planted with the same density in monoculture and in mixture with ryegrass in a fixed device. After yields of plants in different treatments were measured, the plant relative crowding coefficient (RCC), which was quantified by de Wit, was estimated. Finally the competition relationships among ryegrass and six other species under different stress and disturbance conditions were determined. The experimental results showed that the competitive abilities of ryegrass were ordinal superior to T. repens, D. glomerata, S. officinalis, I. cylindrical, M. sinensis and S. japonica var. nepalensis. Moreover, the competitive ability of ryegrass increased when cutting frequency, moisture and soil fertility increased. Cutting frequency was the most important factor to affect competitive ability of ryegrass among the 4 factors studied. On the other hand, the experiment indicated that the growth rate, competitive ability and cutting disturbance tolerance of cultivated herbage (ryegrass, T. repens and D．glomerata) were higher than that of wild species. However, the stress resistance of cultivated plants was lower than that of wild species. When environmental stress increased, cultivated plant’s competitive ability relative to wild species would weaken, and wild species would predominate in the pasture. Meanwhile, the experiment implied that for ryegrass, S. japonica var. nepalensis was a plant of stress tolerance (S) in 6 studied species, T．repens and D．glomerata belonged to plants of disturbance tolerance (D), and the other species were intermediate in stress and disturbance tolerance.