The effect of sheep urine on clover performance in a grazed upland sward

Abstract

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...

Complex dynamics in a carbon-nitrogen model of a grass-legume pasture

“…This may explain why clover content may become low, but few accounts proceed to explain how co-existence is achieved; that is, how a range of mixtures of low clover content are nonetheless sustained. Studies of the dynamics and the cyc1ing and fate of N from urine patches (temporally and spatially heterogeneous environments) have been made (see Ryden, 1984;Bristow, Ryden and Whitehead, 1987;Marriott, Smith and Baird, 1987), and these c1early re1ate to the perturbation and alternation of species advantage explored here. However, the model predicts co-existence even with constant N inputs.…”

Senescence and decomposition of white clover stolons in grazed upland grass/clover swards

“…The relative importance of each route is determined by the quantity of N cycling, the losses associated with the pathway and also the timescale of recovery of N by plants. As regards excretal return, N in urine is rapidly recycled, but this is a relatively inefficient pathway, with very low recovery rates in herbage (Keeney and MacGregor, 1978;Ledgard and Saunders, 1982;Marriott et al, 1987;Thomas et al, 1988). Furthermore, urine return is patchy (Jackman, 1960;Petersen et al, 1956) and therefore recycled N will be unevenly distributed over the sward.…”

Structure and dynamics of grazed vegetation

“…There are effects on canopy structure; increased dry matter production in urine patches results from both increased size (weight and height) of individual grass tillers and N stimulation of tiller production [41]. Some aggregation in excretal distribution may occur; at a high sheep stocking density, the distribution of excreta followed a negative binomial distribution [46].…”