Measurements of rates of growth and senescence of leaf lamina per tiller and of changes in tiller population densities were made in three experiments designed to investigate the influence of sward state on leaf turnover and net production under continuous stocking.In each experiment initially uniform swards were fenced to provide four plots on which animal numbers were adjusted twice weekly to give a series of swards maintained as nearly as possible in a steady state with respect to sward surface height (range I1-6-4 cm) and herbage mass (range 440-2690 kg

A series of twenty-four swards containing different proportions of white clover (OOO-O55) and perennial ryegrass were created by using different seed mixtures, herbicide applications and previous cutting frequencies. These swards were used to study the diet of oesophagcally-fistulated wether sheep which grazed the various swards for a 30-min period after 1. 2 and 3 weeks of regrowth.The proporiion of white clover In the diet was generally greater than that in the sward. Fiftyseven percent ofthe variation in the proportion of white clover in the diet could be attributed to the proportion ofwhite clover in the sward. White clover and perennial ryegrass leaf and stem were grazed to the same height and the proportion of white clover in the grazed horizon of the sward explained 83% ofthe variation in the proportion of white clover in the diet. The proportion of white clover in the diet was greater than the proportion in the grazed horizon of the sward in week 3 of regrowth, but not in weeks 1 and 2. and greater when the proportion of white clover in the grazed horizon was lower than 0-40. Both these observations were interpreted as indicating selec-tion for white clover by the sheep within the grazed horizon.There was a positive and linear relationship between ,the depth of the grazed horizon and sward height which, together with the relationship between the proportion of white clover in the grazed horizon and in the diet, would allow the prediction ofthe proportion of white clover of the diet from the height and the white clover content of the grazed horizon of the sward.

Growth measurements were made on Lolium /jerenoe-dominant vegetative swards during 4-week regrowth periods following grazing or cutting.In the grazing study, the ryegrass (Lolium perenne) swards were grazed for 12-d periods with stock numbers set according to initial herbage allowances per animal of 16, 32 and 64 kg organic matter per sheep. One area was grazed in summer and another area in the autumn.In the cutting experiment four ryegrass swards growing in boxes were prepared by cutting to either 2 or 6 cm at either 14-or 28-d intervals. The swards were cut back in autumn to 2 or 6 cm. During the regrowth period half the boxes were retained in full light and half shaded to 48% of incident light.Herbage weight, rates of leaf extension, senescence, leaf appearance and tillering, water soluble carbohydrate reserve levels in tiller bases and, in the cutting experiment, sheath tube lengths and lamina lengths of leaves which had grown through the sheath tube were measured at intervals during Ihe regrowth period.Final herbage weights reflected management history but net herbage accumulation over the four-week regrowth period, though affected by season, pretreatment and light level, was similar on swards subjected to different grazing or cutting treatments.This result was partially explained by changes in the balance between growth and senescence per tiller as herbage weight increased with time during regrowth. and partially by the reduced production per tiller in harder-grazed swards being offset by a rapid increase in tiller numbers.There was a positive curvilinear relationship between lamina length and the length of the sheath tubes through which the laminae emerged.Carbohydrate reserve levels declined rapidly after grazing or cutting, the extent of the decline being related to the severity of the defoliation. Recovery commenced after four days in summer and was complete within 3 weeks but reserve levels remained low in plants grazed or cut in autumn.The need is discussed for more detailed descriptions of sward states in management studies and for more infonnation on component processes of growth, the factors affecting them and how these interact with different kinds of management systems.

Patterns of defoliation in perennial ryegrassdominaled swards were examined in two experiments. In Experiment I measurements were made on four swards after a single overnight grazing. In Experiment 2 observations were made repeatedly on marked tillers in two continuously stocked swards which were grazed down over a 24-d period. In both experiments the chance of defoliation was related to lamina height both within and between age classes. Lamina angle was measiired in Experiment 2 and within age classes the chance of defoliation was also independent of lamina angle. In Experiment 1 tillers most frequently had both of the two youngest laminae grazed; in Experiment 2 tillers with only lamina 1 grazed occurred most frequently, but defoliation of the two youngest laminae was again common.The difierent frequencies of grazing of the different cla.sses of laminae is interpreted as being a function of their frequency of occurrence within the grazed layer at the top of the sward, 'I'he pseudostem apparently restricted the depth of the grazed layer in the very short swards of Experiment 2.Grazing behaviour in relation to sward structure and the patterns of defoliation and their implications for herbage production are discussed.

The effects of sheep grazing on the development and production of heather swards were studied over a period of 3 years in an experiment in which sheep numbers were adjusted to remove 0, 40% or 80% by weight of the current season's shoots in summer and in autumn. The number of shoots grazed increased with the level of grazing but not in direct proportion. The length of shoot grazed was greater at the 80% level of grazing. Heavy autumn grazing was associated with frequent uprooting and breaking off of shoots and with a high incidence of shoots grazed down to the previous season's wood. The siting of new season's shoots was influenced by the amount of shoot length grazed in the previous season. Grazing behaviour of sheep within a plot was affected by variation in heather cover with the sheep showing a tendency to graze near bare areas. After 3 years of grazing, standing crop was reduced by both levels of grazing whether in summer or autumn. New shoot production was unaffected on plots which had had the 40% level of shoot removal but was reduced by half on plots which had had the 80% level of shoot removal whether in summer or autumn. A clipping experiment was also carried out where 0, 40% or 80% of the length of current shoots was removed in May, early July and Septeinber. Standing crop was unaffected by May clipping but was reduced on plants with a history of 80% shoot removal in July or September. New shoot production was only reduced on clipped plants which had been subjected to 80% removal in September. The role of overwintering green shoots and carbohydrate reserves in the support of new shoot growth was considered. The implications of the results in relation to heather management are discussed.