The effect of artificially applied urine on clover performance in a perennial ryegrasswhite clover sward grazed by sheep was examined during summer. Sheep urine or deionized water (5 1/m 2 ) was applied to areas (2-70 x 1-25 m) which were protected from subsequent excretal return by graze-through cages. Grass and clover populations, nitrogen-fixing activity, soil nitrogen and soil pH were monitored over the following 90-day period.Urine reduced clover population density, stolon length and dry weight but had little effect on number of grass tillers. Nitrogen-fixing activity of clover was reduced initially to less than 30% of control values, perhaps owing to high levels of soil inorganic nitrogen inhibiting fixation, although osmotic effects due to the high salt concentration in urine cannot be discounted. The lower levels of activity at later dates were due largely to reduced clover in urine-treated areas. Soil pH (0-5 cm) was increased by about 0-5 units 3 days after urine application, with a smaller increase in the 5-10 cm horizon. Recovery of urine nitrogen in the soil mineral N pool was at best 27% of the added nitrogen.The results are discussed in terms of the significance of urine-affected areas in determining a patchy distribution of clover in grazed swards; the role of animals in the transfer of fixed N from clover to grass is considered. a n d nitrogen-fixing activity of white clover (Ledg a r d g t e e l e & S a u n d e r 8 1982 ) have been studied In upland areas of the U.K. white clover can make previously, mostly in cutting or rotationally grazed an important contribution to the nitrogen economy experiments, under better climatic conditions than of mixed swards and increase the quality of herbage those in upland areas of the U.K. In this paper the for grazing animals (Newbould, 1979). However, the short-term effects of urine on clover performance in unpredictability of performance of mixed swards a continuously grazed upland sward stocked with and the difficulty in maintaining a high clover sheep are reported, content partly explain a reluctance amongst farmers to adopt clover-based systems (Frame & Newbould, MATERIALS AND METHODS 1984). Information is required from grazing experiments to elucidate the reasons for these problems, Site so that clear guidelines for the management ofThe experimental site was a poorly drained, nongrass-clover swards can be established.calcareous gley of the Rowanhill Series, at an altitude Grazing animals influence pasture production via o f 220 m. Perennial ryegrass (Lolium perenne cv. defoliation, treading and excretion of faeces and Perma) was sown in 1982, and white clover (Triurine. Most of the nutrients ingested by animals are folium repens cv. Huia) was slot seeded into the returned to the pasture; about 80% of ingested N is sward in 1983. The sward received no nitrogen excreted, mainly as urine (70-75% of the total fertilizer in 1984 or 1985 and was maintained at a excreted N). The urine-affected areas of a sward m e a n s w a r d surface height of 3-5 cm by adj...
The fate of marked sections of stolons of white clover (Trifolium repens) over a 50-week period from May 1987 was followed in grazed grass/clover swards maintained at 5-cm sward surface height with and without N fertiliser. There was little effect of N treatment on the pattern of survival of stolon sections. The proportion of live stolons recovered decreased during the experiment, and in May 1988 on average only 29% of the marked sections remained alive. At all harvests only a small percentage of stolon sections showed signs of senescence; the maximum percentage, on average 20% of those marked, occurred in autumn, 15-20 weeks after marking. Following this period, i.e. in late autumn/winter, the most rapid increase in percentage of decomposed stolons was measured. Over 50% of stolon sections were buried within the 5-week period following marking and nearly all were buried after 20 weeks; generally a much smaller proportion of stolon tips was buried. Nutrient concentrations of N, P and K fell to their lowest levels in autumn, before increasing in the following spring. Results are discussed in relation to the cycling of nutrients via stolon senescence.
The growth of tree lupins was investigated in two experiments. In the first, two ages of plant, 4-wk-old seedlings and l-year-old plants, were transplanted into a ryegrass sward in an upland environment. Growth, in terms of leaf production, branching and stem elongation, was measured over two successive growing seasons. Plant dry matter and nutrient contents were determined at the beginning and end of each growing season. In the first summer, the rate of production of new leaves on the main stem of seedling plants averaged 1.8 leaves per wk and main stem length increased from 5 to 67 cm. On older plants, where floral apices had been initiated on main and primary stems, there was a 3-10 fold increase in secondary branch length. In the second season, there was no effect of plant age on rates of leaf appearance or stem extension; dry matter production was higher than in the first season.In the second experiment, the effect of removal of 0%, 50% or 100% of fully expanded leaves on the subsequent growth of 23-wk-old plants was investigated. During the 7-wk growth period, defoliation promoted the rate of production of mature leaves, and area and dry weight of new laminae were slightly higher in defoliated plants. Defoliation did not affect the concentrations of N, P or K in the new laminae, but P and K concentrations in petioles of defoliated plants were significantly higher than those in intact plants.The results from the experiments are discussed in relation to the potential use of tree lupins as nurse species and biomass crops in hill and upland environments of the UK.
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