Second-cut silage has been a smash-and-grab effort so far, with some yet to be harvested.

While dry matters of harvested grass in May and June had been high and posed a low risk for effluent production, recent wet weather and shorter wilting periods have meant that the dry matter of recently harvested grass is much lower.

A tonne fresh weight of harvested grass can produce from 0 to 350 litres of effluent.

Risks of effluent

Silage effluent is highly pollutant and can cause major pollution to groundwater and aquatic life in watercourses.

The first step to managing silage effluent is to try to limit its production through harvesting dry grass.

Generally, harvested grass of a 25% dry matter or higher will produce little to no effluent.

A 24- to 48-hour wilt with good drying conditions will usually achieve this, but current dry matter of fresh grass is 12% to 14%, which will make this more challenging.

Where harvested grass is of a lower dry matter, a 75mm corrugated drainage pipe should be installed in effluent channels to help prevent blockages of channels.

Channels should be 75mm x 75mm to ensure adequate capacity. Silage covers should extend past this channel to prevent rainwater entering the effluent channel and tank.

The majority of effluent will be drained from the pit in the first two weeks post-harvesting, so attention must be paid to the effluent tank, so that overflowing does not occur.

Any cracks on the pit floor that is due to be soon filled will need to be repaired immediately to prevent seepage of effluent. Hot bitumen, similar to that used in expansion joints, will likely offer the quickest repair, although seriously degraded slab floors should be extensively repaired or replaced.

Silage effluent should be spread at a 1:1 ratio with water or slurry; 5m buffer zones along watercourses should be adhered to, and no effluent should be spread within 48 hours of forecast rainfall.

When silage pits are open, the floor of the pit should be kept clean as silage is removed from the pit. At the point where farmers are feeding silage, all effluent will have drained from the pit and it will be diverted to a clean water runoff.

Silage or soil from vehicle tyres on the pit floor have the potential to pollute the rainwater being drained in to this clean water runoff.

Storage of bales

New rules have come in to play this year for the storage of bales, mainly due to effluent production from stacked bales. Baled silage is generally higher in dry matter due to longer wilting periods, but the common stacking of bales can create issues. Single stacked bales can emit up to 24l of effluent per tonne of silage, with this rising to 41l for double stacked bales.

Where ther is no means of collecting and storing effluent, silage bales can not be stacked greater than two high.

The new rules, signed into law last year and effective from this year, dictate that silage bales should not be stored greater than two high unless there is appropriate means of collecting and storing effluent.

Silage made last year that is stored greater than two high will not incur penalties, but on-farm inspections are being carried out by the Department regarding bales made this year.

Farmers must also be aware of cross-compliance rules that dictate that bales can not be stored within 20m of a waterbody. This includes dry drains; if it has the capacity to carry water then it is classed as a waterbody.