In many countries, environmental regulations are in place to control the management of effluent on-farm. Local and national regulations must always be adhered.
Effluent production by forage is a combined result of:
- Dry Matter (DM) of forage
- Forage type
- Nitrogen fertilizer application
- Conditioning of forage at harvest
- Chop length of forage
- Compaction of forage
- Treatment of forage
As the DM of the forage rises then the amount of effluent that will be produced per ton of forage drops. Quite simply, there is less liquid present that can be squeezed out of the forage. Equally, if the forage is ‘conditioned’ when mowed, or chopped very short, potentially effluent can be produced until a forage DM is reached where no effluent can be produced.
Historically, accepted wisdom was that once we reached 30% DM effluent will no longer be produced. This logic was based on bunkers and drive over piles, and the reality is that with bales and AgBags we can produce silage at lower DM without an issue with effluent.
Since the turn of the 2010’s equipment for compaction has significantly improved, meaning when ‘train-wheel compactors’ are used the potential density that can be achieved is higher than previously encountered, and that effluent can be produced at DM up to 32%.
The chart to the right indicates the volume of effluent that can be produced in bunkers and drive over piles at different ensiling DM, with the recommended packing density for the different DM).
What is Effluent?
Silage effluent is a high nutrient liquid waste product from low DM silage. Typically it has a pH of between 3.5 – 5, making it highly corrosive to both metal and concrete and capable of damaging the silage storage structure. In addition, it is highly poisonous to watercourses with 1 liter of silage effluent containing sufficient organics to reduce the dissolved oxygen in 10,000 liters of water below critical levels for fish survival (Gebrehanna, 2014; Cropper and DuPoldt, 1995; Mason 1988). In essence, silage effluent is 100 times more environmentally potent than raw sewage meaning that effluent is a potentially disastrous contaminator of fresh water courses.
The nitrogen, phosphorous, and potassium concentration of silage effluent is similar to that of liquid slurry, making it a useful fertilizer but one that should be carefully managed if being mixed with slurry for field application due to the potential production of hazardous gases such as hydrogen sulfide.
Different forages will produce different levels of effluent under similar conditions. The use of any kind of inoculant or additive will raise the volume of effluent produced, with acid additions leading to a greater production of effluent than inoculant application.
Equally, use of nitrogen fertilizer, short chop, conditioning, and high compaction will elevate the level of effluent production.
*Figures are subject to variability (Adapted from Jones)
(19% DM Ryegrass. Jones)
Bales are generally made at high dry matter levels and as such are often not prone to effluent production, however, when bales are made at lower DM levels they are subject to the same issues as bunker or drive over pile silage. Bales generally should not be stacked as the plastic and net around the bale is only meant for the weight of bale and slippage of plastic occurs leading to air penetration into the bale (molding, increased DM and feed value losses), but when the bales are at a lower DM the volume of effluent that generated elevates with stacking.
Effluent adversely effects the fermentation of forage and can encourage the formation of undesirable acids and ammonia. In anticipation of the effluent production from forage and its dissemination in the environment, it’s important to install an effluent collector at the silo entrance.
Then, the only true way of managing effluent is to stop its production by harvesting at a sufficiently high DM, though the amount of effluent produced can be mitigated by boosting the length of the forage chop at ensiling, reducing the level of compaction of the forage or by including layers of adsorbent material such as straw. We also advise farmers to install an effluent collector at the silo entrance to avoid any environmental contamination.