Summary Clonal growth and fragment regeneration of Rumex obtusifolius L. were analysed in two dif ferent studies. Clonal growth system was des cribed by a morphological study of underground structure of different‐aged individuals, using maximal branching order in the stem system as an age estimator. Glasshouse experiments were conducted, testing the regenerative capacity of different below‐ground parts and the estab lishment of above root‐collar fragments planted at different depths under contrasting water regimes. Results showed the presence of a ‘phalanx’ type clonal growth system in grassland populations of Rumex. The main structure in volved in clonal growth proved to be the stem system; the region above the root collar was also the only part able to regrow after damage. Stem fragment regeneration occurred to depths of 15 cm, but was prevented in soils maintained at waterlogging and field capacity. The significance of these results in relation to nonchemical con trol of Rumex populations in grasslands is discussed.

A preliminary field experiment on a sward cut six times during 1978 indicated that total grass herbage harvested was negatively related to the number of Rumex obtusifolius plants present; densities of five to ten plants m"^ resulted in reductions of up to 30%, although the total quantity of herbage harvested (including Rumex) may have remained constant. However, R. obtusifolius densities did not significantly affect grass yield during the first half of the growing season. A negative relationship between R. obtusifolius ground cover and grass yield, particularly from late July onwards, was shown in a second field experiment during 1979 and 1980 using a 3-cut management. It was estimated that to produce a 20% reduction in grass growth in Juty-August and October, R. obtusifolius ground covers of 30% and 20% respectively were needed. Sixty per cent of the total herbage harvested in 1980 consisted of ^. obtusifolius. These results indicate the damage that can be caused by this species and suggest that control measures should be taken before early summer.

To rectify the lack of comparative data on the productivity of some commonly occurring indigenous grasses, seasonal growth curves were obtained during the first year of a 3-year study by harvesting monoculture plots of Holcus lanatus, Agrostis stolonifera, Festuca rubra, Poa trivialis and Lolium perenne (cv. S23) at monthly intervals in a staggered sequence. Under conditions of high soil fertility (40 kg ha"' N per defoliation and frequent irrigation) the daily production of dry matter by P. trivialis followed the familiar two-peaked pattern of L. perenne, albeit at a lower level after flowering. By comparison, F. rubra and A. stolonifera grew more uniformly throughout the year; H. lanatus, like F. rubra, was noticeable for its high productivity after midsummer. With monthly cutting all four indigenous grasses had a higher mean nitrogen content compared with L. perenne; mean digestibilities were also comparable with the exception of F. rubra.During the second year, when inputs of nitrogen and moisture were lower, primary spring growth was most rapid with H, lanatus and F. rubra but the high digestibility of L. perenne meant that harvesting could be delayed to obtain the most forage of a given D-value. Regrowth, measured from cuts taken in" early August and September, was greatest with A. stolonifera and F. rubra respectively.Dry-matter responses to a total of 60 and 180 kg ha~' N, applied in three applications on a split-plot basis, were recorded during the last year. Apart from the early nitrogen application, the indigenous grasses Correspondence: Dr R. J. Haggar, ARC Weed Research Organization, Begbroke Hill, Yamton, Oxford. OX5 lPF. responded well, except for A. stolonifera, especially after flowering. Though the response of L. perenne was consistently high throughout the summer, at least 20 kg DM per kg N, it yielded least of all the grasses at the low nitrogen level.The agricultural significance of these results are discussed. It is concluded that whereas L. perenne performs well at high levels of nitrogen and moisture, the other species do better than L. perenne, especially during mid-season, when these factors are limiting.

The results are reported of the effects of fertilizer and grazii^ or cutting for hay over a period of 6 years on the composition of an Agrostisj Festuca permanent pasture on low-lying land at Beghroke Hill. Applications of N up to 264 nnits/ac each year associated with frequent defoliation every 21 days produced only smalt changes in sward composition; Agrostis spp. declined and Poa triviaiis increased. Lolium perenne did not increase from a small initial presence. Records of aniinal performance and hay yield showed that the mean output from the experiment as a whole was 530 Ih liveweight gain/ac and 0*5 ton hay/ac.