Ensiling of Manured Crops—Does Repeated Spreading of Slurry Increase the Hygienic Risk?

Abstract

The influence of cattle slurry applied to a silage crop was studied in three successive years. Each year, 40 t slurry ha-1 were applied in two equal applications. Unfertilised and mineral-fertilised field plots were used as controls. Before spreading, the slurry was contaminated with spores of Clostridium tyrobutyricum (103–104 g-1 FM). The fields were harvested two times a year, the yields were measured and the chemical composition and bacterial content of the crop were determined. The fresh material was chopped, ensiled without additives, and stored for 100 days before opening. The bacterial content of the soil surface and available N, P and K in soil were measured. Slurry did not seem to have any significance in a short-term perspective. Yield increase as an effect of slurry application was slight and inconsistent in comparison with the yield from unfertilised plots. The number of Clostridium or Bacillus spores in the soil surface was not significantly affected by the slurry application, nor was the number of detrimental organisms in harvested crop at ensiling. Nonetheless, in three of the four silages in which clostridial spores were estimated, numbers were higher in silage made from slurry-treated crops. © 1997 SCI.