Two 2×2 factorial experiments are described in which a bacterial inoculant being developed as a silage additive and containing a strain of Lacto‐bacillus plantarum (Ecosyl, ICI plc) was evaluated at two harvests (18 July and 30 September 1985) of two swards (perennial ryegrass and permanent pasture) in difficult ensiling conditions. On each occasion erbage was ensiled with and without inoculant using two 0·5–t capacity steel tower silos per treatment. The contents of the two replicate silos per treatment were combined for feeding to cross‐bred wethers in digestibility and metabolizable energy (ME) partition studies. Overall, inoculated herbage declined in pH post‐harvest at a faster rate than control herbage (p<0·001) and three out of the four inoculated silages had lower pH, ammonia‐N, acetate and alcohol and higher residual soluble carbohydrate content (p<0·001) than control. Significantly higher digestibility of nutrients (P<0·05) was found in three of the inoculant‐treated silages and these also had significantly higher ME values than control (P<0·001), (10·58 and 8·77 MJ kg tol DM−1 for the treated and untreated silages respectively). The use of inoculant on herbage of only moderate ensiling potential therefore, produced significant improvements in fermentation quality and feeding value over control.

Two 2x3 factorial design experiments were conducted during 1985 to compare the effect of treating grass at ensiling with a silage inoculant (Imperial Chemical Industries pic) or formic acid with an untreated control, on fermentation, insilo losses, intake and performance of finishing cattle.In experiment 1, three covered concrete-walled silos were each filled with approximately 70 t of primary growth, unwilted herbage at each of two cutting dates, 20-21 May (early harvest) and 3 June 1985 (late harvest). In experiment 2, the above procedure was repeated for second regrowth grass with two cutting dates, 30 September-1 October (early harvest) and 16-21 October 1985 (late harvest). The water-soluble carbohydrate (WSC) contents of the herbage were low in both, being 130-160 and 121-137 g kg-' DM for the first and second experiments respectively. In both experiments the formic acidtreated silages attained lower temperatures than Correspondence: Dr S, J, Kennedy, Experimental Husbandry Department, Greenmount College of Agriculture and Horticulture, Antrim BT41 4PU, Northern Ireland, UK, the inoculant-treated and untreated silages. At both harvests in experiment 1 the pH, ammonia nitrogen CNH3N) and volatile fatty acid (VFA) contents of the inoculant-treated and formic acidtreated silages were significantly lower than those in the untreated silage. However, at the early harvest in experiment 2 the pH and NH3N contents of the inoculant-treated silage were significantly higher than those in the two other silages. At the late harvest in experiment 2 the inoculant-treated and the formic acid-treated silages had significantly lower pH and VFA contents than the untreated silage.After 126 d and 98 d storage periods in experiments 1 and 2 respectively, each of the six silages was offered to twelve 475 kg steers throughout a 70-d period (experiment I) and a 63-d period (experiment 2). In exf>eriment 1 there were no significant effects of additive on silage DM intake, liveweight gain or carcass gain with the mean carcass gains being 0 49, 0-51 and 0 52±0 024kgd-' for the untreated, formic acidtreated and inoculant-treated silages respectively. In experiment 2 the mean silage DM intakes were 634, 7 33 and 660±0151 kg d"' and carcass gains were 0 27, 0 35 and 0 26±0 026 kg d"' for the untreated, formic acid-treated and inoculanttreated silages respectively, formic acid treatment thus gave the most consistent results.

Eight field-plot experiments were carried out on established grassland swards between 1984 and 1988 to examine the effects of date and rate of application of calcium ammonium nitrate (CAN) on herbage dry matter (DM) yield and apparent efficiency of nitrogen (N) use at firstcut silage.CAN application significantly increased (P<0-001) the mean yields of herbage and N uptakes by herbage in all experiments. Herbage yields were similar (P>0-05) with N rates of 100 kg ha"', 125 kg ha"' or 150 kg ha"' in five experiments but in the other three there were increases above 100 kg ha''. Date of N application had a'significant effect on DM yield in three experiments; this effect was inconsistent for both single and split dressings. Lower production was associated with reduced uptake of N, a trend that primarily refiected lower DM yields and not wide herbage N content variation.It is concluded that selection of the date on which to apply fertilizer N in early spring to obtain optimum herbage yields at first-cut silage often required little precision. The use of fertilizer N rates >100 kg ha'' should be questioned where there are likely to be appreciable quantities of available N derived from non-fertilizer sources.

S U M M A R YField plot experiments were carried out for 3 years at four sites to study the effect of date of application of ammonium nitrate/calcium carbonate (CAN) and urea (U) on perennial ryegrass production in spring. Fertilizer (70 kg N/ha) was applied at weekly intervals for 10 weeks from 1 February. Herbage was cut on the same day at all sites, 3-4 weeks after the last N application. CAN and U at 50 kg N/ha were immediately re-applied and a second cut of herbage was taken after 4-5 weeks. From meteorological data, the dates after 1 February when soil temperature at 100 mm depth increased to 5-5 °C and the dates when cumulative average daily air temperatures > 0 °C from 1 January reached 200 °C were calculated for each site and year.The date of application for maximum dry matter (D.M.) yield at the first cut differed with site and year, but for 11 of the 12 site/years was in February. The number of dates of application resulting in optimum yield (i.e. at least 90% of the average maximum yield response to CAN or U) varied also with site and year from one to six. Soil and air temperature predictive systems implied a precision in choice of application date that was unjustified and were no more successful at predicting the optimum application date than a simple date range. The first fertilizer application had a pronounced positive residual effect on D.M. yields at the second cut. Less precision on date of the first application was required to obtain optimum cumulative yields over both cuts than optimum yield at the first cut only.Differences in performance between CAN and U were only significant for three of the 120 fertilizer applications at the first cut. On these occasions, all in one year at two sites, U gave higher yields than CAN. Correlations were sought between D.M. yield response and growth period, air temperature, long-term rainfall and short-term rainfall for CAN and U separately. Factors relating to rainfall had no significant effect on response to U but response to CAN showed a significant negative correlation with short-term rainfall. The short-term weather forecast may therefore be another criterion to be considered in deciding when to apply N in early spring.

No abstract