Tips for grain pits

Brett Littler - Senior Land Services Officer, Livestock

We have been running some silage, hay workshops over the last few weeks. One question that I am starting to get regularly is about grain pits and what tips I recommend.

Grain Pits are a great way to store grain for short or for long periods (one grain pit opened in 2018 was put down in 1982) and is a cheap easy way if done properly. So how do you do it properly and what grain is suitable to put in a pit?

There are several tips to ensure your grain pit is a success:

LOCATION:

• Preferable hillsides - this allows for a sloping pit floor.
• Avoid stony areas- water moves more freely and stones can puncture plastic.
• Relatively flat areas are successful providing soils are clayey and joins in plastic overlap well.

CONSTRUCTION:

• Pits should not be greater that 3 m wide at the top. This allows soil covering and removal with a front end loader without driving on the grain. Grain also keeps cooler, which aids in safe storage.
• Pits should be wider at the top, to prevent cave-ins whilst filling and emptying.
• Depth of pits are usually around 2 m, but can be deeper.
• Pits sizes ideally match silo capacity. When emptying, grain can be immediately transferred to reduce risk of weather damage on the open pit.
• Pits should be dug in spring, as soon a estimates of crop yields are feasible, and moist soil allows easier digging.
• Floor of pit should be level as "bumps and hollows" can trap water when filling.

FILLING:

• Cereal grain should be less than 12% moisture.
• Be careful of collapsing walls if grain is being tipped in.
• Use 200 micron plastic.
• Sides of the pit are lined, just ahead of the grain, as filling occurs.
• The plastic wall lining should overlap well at the centre of the top of the pit.
• Lining the bottom of pits eliminates wastage when emptying.
• If using old grain pits, apply "clean up" insecticides to the pit. Weevils that may be present can cause considerable damage in the newly filled pit before oxygen is finally depleted.
• In freshly dug pits treating with an insecticide is not necessary, providing uncontaminated grain is used.
• During the filling of the pit, if rain occurs before the grain can be covered, water will shed, if the grain is peaked. Ensure the grain in the pit is completely dry (less than 12% moisture for cereals) before continuing filling.
• Floor surface should be dry also. Soil sub surface moisture however will only damage a thin layer of grain.
• Pits, when full, should have grain peaked above the soil surface. This assists drainage, as grain does not "settle".
• It is a good idea to have a few old motor tyres on site, to keep the plastic from blowing about.
• Take care not to puncture the plastic when rolling out….stones, thistles "stumps" etc.

COVERING:

• Plastic used for the walls must overlap the centre of the top of the pit by approximately 1 m.
• A top sheet of plastic is placed over the pit, extending one metre each side of the pit.
• A 10 to 15 cm layer of straw is placed on the plastic, before covering with soil. This is helpful when the pit is uncovered:
  • alerts operator that the plastic is close
  • prevents soil sticking to the plastic
  • For long term storage use a thin layer of sand).
• Cover with 0.5 metres of soil, making sure the soil is slightly hilled/peaked.
• Any joins in the plastic should overlap by at least 150 mm. Ducting tape can be used for a perfect seal. Where tape is not used on sloping sites overlap by at least 300 mm and ensure the overlap sheds any water onto the adjoining layer.