Pollution problems caused by silage are mainly odour and effluent production.

Odour can be virtually eliminated by ensuring a satisfactory silage fermentation, i.e. a low pH and a low ammonia concentration in the total nitrogen. This can be achieved by following the basic rules of good silage making, including the correct use of an effective acid additive.

Effluent is the major problem, particularly when it enters drains and water courses. This is because a typical effluent will have a pH of approximately 4.0 and a high 5-day biological oxygen demand (BOD5) up to 90 000 mg O2, per 1. This compares with BOD5, values of 5000 and 500 mg O2 per 1 in cow slurry and untreated domestic sewage respectively. Thus silage effluent in water courses removes the dissolved oxygen and will kill fish and other aquatic fauna. Effluent from a silo containing 300 t of low dry matter (DM) silage is equivalent in BOD5 to the daily sewage from a town of 80 000 people.