EFFECT OF LONG-TERM APPLICATION OF ANIMAL SLURRIES TO GRASSLAND ON SILAGE QUALITY ASSESSED IN LABORATORY SILOS

The effect on silage quality of slurry type (pig or cow), rate of application of slurry (50, 100 or 200 m(3) ha(-1) year(-1)) and use of a bacterial silage inoculant, was assessed on grass from a long-term slurry experiment ensiled in laboratory silos. There was no significant effect of slurry type on the quality of silage made from grass regrowths. However, on the basis of ammonia-N, lactate and volatile fatty acid contents, spring (first cut) grass treated with cow slurry in both years of the study produced significantly poorer fermentation (P < 0.001) than silage from grass treated with pig slurry. The quality of silage made from slurry-treated swards compared favourably with that from swards treated with granular fertiliser. Although increasing the rate of slurry application was shown to reduce fermentation quality in most treatments, this was seen as an effect of increasing the total-N content of the herbage rather than of slurry application per se. From a study, in selected treatments, of the bacterial flora at harvest, it was also observed that slurry application had little impact on either the composition or diversity of herbage enterobacteria at harvest, and therefore probably upon subsequent fermentation. No evidence was found for the occurrence of clostridia on herbage from slurry-treated swards. Use of a bacterial inoculant (Ecosyl; ICI plc) improved fermentation quality significantly (P < 0.001) even where high rates of slurry (200 m(3) ha(-1) year(-1)) had been applied to swards. The high acetate and butyrate contents typical of laboratory silages untreated with additive, were not seen in the inoculated silages.