ALBERT

Description: SUMMARYTiller weight, lamina length, lamina growth rate, appearance interval and lamina utilization were examined in Lolium perenne, Agrostis stolonifera, Holcus lanatus and Poa trivialis. Marked tillers were measured in situ over 14–21 day periods in a continuously grazed permanent pasture under steady state management in Devon, UK, in 1985, 1986 and 1987 on plots receiving either zero (0N) or 400 kg nitrogen (400N) fertilizer/ha per annum.L. perenne was incapable of reducing its individual tiller weight or lamina length to the same extent as in the other three species during the grazing season. Lamina appearance interval was longer in L. perenne than in the other three species in most of the observation periods in both the 400N and 0N plots. Overall the lamina appearance intervals were similar between A. stolonifera, H. lanatus and P. trivialis. Lamina extension rates were greater in L. perenne than in either A. stolonifera or P. trivialis in most observation periods in both plots. H. lanatus had lower lamina extension rates than L. perenne in c. 50% of the observation periods in both plots, at other times the extension rates of the two species were similar, with one exception in early spring in the 400N plot when H. lanatus had a higher extension rate. There was no clear pattern in seasonality as to when H. lanatus had a lower extension rate than L. perenne. H. lanatusachieved either similar or higher lamina extension rates than either A. stoloniferaor P. trivialis in c. 50% of the observation periods, respectively; the periods when higher rates were observed in H. lanatus in the 400N plot occurred mainly in the spring and early summer. A. stolonifera and P. trivialis achieved similar lamina extension rates in most observation periods in both the ON and 400N plots. The specific differences observed in the lamina extension rates were emphasised when converted to growth rates by multiplying the length increments by the average weight per unit length of the expanded lamina for each species.Lamina utilization, in terms of percentage of lamina length removed by grazing, was similar between the four grass species in most observation periods in the ON plot. A. stolonifera lost more lamina length than either L. perenne or P. trivialis in May and June and H. lanatus lost a greater percentage of lamina length than either L. perenne or P. trivialis in May in the ON plot. In the 400N plot L. perenne lost a greater percentage of lamina length than any of the other species in June and more than P. trivialis in May. A. stolonifera lost a greater percentage of lamina length than any of the other species in July, and more than either L. perenne or P. trivialis in May. This greater severity of grazing in A. stolonifera was associated with a high incidence of tillers being grazed to stubble. H. lanatus lost more lamina length than L. perenne in May. When the loss of lamina length through grazing was converted to losses in terms of weight of tissue removed, then L. perenne consistently lost more than either A. stolonifera or P. trivialis in both the 400N and 0N plots.The implications of these differences in tissue production and utilization on competitive interactions between L. perenne and the other three species are discussed.

Description: SUMMARYThe response of an old, unimproved mixed-species pasture to fertilizer nitrogen was examined under 4-weekly cutting or continuous grazing with young beef cattle. Five N fertilizer rates were applied: zero, 100, 200, 400 or 800 kg/ha per year. The investigation was carried out in Devon, on a heavy clay soil in a region of high winter rainfall in 1984, 1985 and 1986.Annual total herbage dry-matter (DM) production, live weight gain (LWG) and utilized metabolizable energy (UME) output all increased with successive increments of fertilizer N up to 400 kg N/ha per year. Under 4-weekly cutting, the response per kg applied N fell below 10 kg DM at an application rate of 268 kg N/ha per year, giving a yield of 10·6 t/ha per year. Under grazing, the overall response during the grazing season per kg applied N fell below 300 kg live weight carried per ha at a fertilizer rate of 248 kg/ha per year, giving a UME output of 78 GJ/ha over the grazing season. High available soil N contributed to the high productivity from these swards. Animal output at moderate (200 kg N/ha per year) N application rates did not appear to be constrained by the initial botanical composition of this unimproved sward. Repeated high N applications in the 400 kg N/ha per year treatment reduced output in 1986 under grazing and cutting, compared with treatments which had received the lower N applications.The DM yield from the 4-weekly cutting study gave a satisfactory prediction of UME output from this pasture. Climatic conditions, particularly high rainfall, appeared to be an important constraint on animal performance at pasture.The high UME output achieved from this pasture at 200 kg applied N/ha was well above the average UME for commercial farms.

Description: SUMMARYThe concentration of nitrogen (N) within the emerging, youngest fully expanded and the youngest dead leaf laminae were examined in the grasses Lolium perenne, Agrostis stolonifera, Holcus lanatus and Poa trivialis in Devon, UK, in 1986 and 1987. Lamina growth, appearance interval and lamina utilization were also examined in each species. Marked tillers were measured in situ over 14–21 day periods in a continuously grazed permanent pasture under steady state management on plots receiving either zero (ON) or 400 kg nitrogen (400N) fertilizer/ha per annum. The concentration of N tended to be greatest in the distal half and least in the basal part of each lamina in each species. Total mass showed an opposite trend due in part to the shape of the lamina. Less than 40 % of the lamina N was lost through grazing either in the ON or 400N plots in the four species, except once in H. lanatus when more was lost. In absolute terms, because L. perenne and H. lanatus maintained larger and longer laminae than either A. stolonifera or P. trivialis, they lost more N through grazing. The four grass species recycled N from the senescing lamina with the same apparent efficiency; this meant that differences in lamina N concentration and carbon: nitrogen ratios were present in the dead laminae of the four species. L. perenne achieved the highest tissue growth rate per unit of N in the lamina in the ON plot, not only in comparison with the three other grasses but also compared with the 400N plot. This high N-use efficiency in L. perenne was not translated into an ability to either expand or maintain its population in the ON plot. L. perenne had a lower leaf appearance rate than the other species in both the 400N and ON plots, but this inherent characteristic of the species was particularly pronounced in the ON plot. A slower leaf appearance rate would limit the potential tillering capacity of L. perenne compared with the other species. A reduced tillering capacity, exacerbated by N deficiency, was probably the principal factor limiting the ability of L. perenne to exploit available niches in the ON pasture.