Runoff of faecal microorganisms and nutrients from perennial grass ley after application of slurry and mineral fertiliser

Perennial grass was fertilised with cattle slurry either surface-spread or injected into the soil. Slurry was spread once (early summer) in 1996 and 1997 and twice (both summer and autumn) in 1998 and 1999. The control was mineral fertilisation in summer. Faecal microbial numbers in surface runoff water were very high in late June 1998 soon after very heavy rains even though the last slurry application had been made almost one year earlier. There was no clear difference between slurry spreading methods. Autumn spreading of slurry lead to high microbial levels in runoff waters and water hygiene was protected better by slurry injection than by surface spreading. In spring, after snow melt, some faecal microorganisms were found in surface runoff water and the numbers of faecal microorganisms were less from plots with slurry surface spreading than those with slurry-injection. Losses of total phosphorus (TP) and total nitrogen (TN) in surface runoff were 2.7 and 7.7 kg/ha respectively from grass with surface-spread slurry in winter 1998-1999. The injection of slurry decreased TP and TN runoff by an average of 81% and 73% respectively. In 1999 there was little runoff because the summer was sunny and dry.