Nitrous oxide (N2O) and methane (CH4) emissions were measured from grassland following manure applications at three times of the year. Pig (Sus scrofa) slurry and dairy cow (Bos taurus) slurry were applied in April, at equal rates of ammoniacal‐N (NH+4‐N), and in July, at equal volumetric rates (50 m3 ha−1). I n October, five manure types were applied to grassland plots at typical application rates: pig slurry, dilute dairy cow effluent, pig farm yard manure (FYM), beef FYM and layer manure. Emissions were measured for 20, 22, and 24 d, respectively. In April, greater cumulative emissions of N2O‐N were measured following application of dairy cow slurry (1.51 kg ha−1) than pig slurry (0.77 kg ha−1). Cumulative CH4 emissions following application in April were significantly greater from the dairy cow slurry treatment (0.58 kg ha−1) than the pig slurry treatment (0.13 kg ha−1) (P < 0.05). In July, significantly greater N2O‐N emissions resulted from pig slurry‐treated plots (0.57 kg ha−1) than dairy cow slurry‐treated plots (0.34 kg ha−1). Cumulative net CH4 emissions were very low following July applications (<10 g ha−1). In October, the lowest N2O‐N emission resulted from application of dilute dairy effluent, 0.15 kg ha−1, with the greatest net emission from the application of pig slurry, 0.74 kg ha−1. Methane emissions were greatest from the plots that received pig FYM, resulting in a mean cumulative net emission of 2.39 kg ha−1.

Storage of cattle slurry is a significant source of ammonia (NH3) emissions. Emissions can be reduced by covering slurry stores, but this can incur significant costs, as well as practical and technical difficulties. In this pilot-scale study, slurry was stored in small tanks (500 L) and the effectiveness of natural crust development for reducing NH3 emissions was assessed in a series of experiments. Also, factors important in crust development were investigated. Measurements were made of crust thickness and specially adapted tank lids were used to measure NH3 emissions. Slurry dry matter (DM) content was the most important factor influencing crust formation, with no crust formation on slurries with a DM content of <1%. Generally, crusts began to form within the first 10 to 20 d of storage, at which time NH3 emission rates would decrease. The formation of a natural crust reduced NH3 emissions by approximately 50%. The type of bedding used in the free stall barn did not influence crust formation, nor did ambient temperature or air-flow rate across the slurry surface. There was a large difference in crust formation between slurries from cattle fed a corn (Zea mays L.) silage-based diet and those fed a grass silage-based diet, although dietary differences were confounded with bedding differences. The inclusion of a corn starch and glucose additive promoted crust formation and reduced NH3 emission. The maintenance of a manageable crust on cattle slurry stores is recommended as a cost-effective means of abating NH3 emissions from this phase of slurry management.

The absorbance at 280 nm was determined for samples of dirty water, and pig and cow slurry effluents collected annually over a period of 3 years. Regression analysis showed an exponential relationship between absorbance and biochemical oxygen demand (BODs). Well fitted regressions of absorbance (280 nm) on BOD5 were obtained for each year, especially for exponential regression analysis. Such regressions were then used to estimate BODs. Once a relationship is established between UV absorbance and BOD, UV absorbance measurements can be used to rapidly analyse large batches of samples, and also to improve the efficiency of the BOD~ test by indicating dilution ranges.

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.

S U M M A R YThe 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.iMTRnnTTTTTOM productive than sown species, such as Lolium perenne, I1N1KUUUL11U1N a t m o d e r a t e t Q h i g h N j n p u t s ( C h a r l e s et at 1 9 7 9 . Old permanent pastures, aged 20 years or more, cover Dibb 1985). However, recent studies by Hopkins et al. c. 3-7 million ha and occupy c.