Ensuring adequate slurry storage and straw requirements this winter

A greater focus on slurry storage has been taken by farmers in the past year due to spiralling chemical fertiliser prices.

Farmers are keener now more than ever to utilise the valuable nutrients in slurry.

This means only spreading organic manures when grass is growing and can take the nutrients from the soil. While the closed period for organic manure application finishes in mid-January, farmers should seek to hold off on spreading slurry or dung further into the spring.

Table 1 charts the slurry and straw requirements for different types of livestock throughout the winter months.

For a dairy cow, a minimum of 0.33m³ is required, the equivalent of 74 gallons. A typical 100-cow herd requiring 16 weeks’ minimum storage will therefore need 528m³ of storage (116,143 gallons).

However, having 528m³ of storage is not enough. Some 200mm of freeboard, a gap between the top of the slurry and the bottom of slats, is required to allow for agitation and to prevent animal welfare issues. The recommendation is to have 20% of a buffer for dairy farms and a 10% buffer for drystock past the minimum requirement.

All the above space requirements are based on internal tanks. Outdoor tanks have a requirement greatly in excess of this due to the volume of rain.

Mean rainfall for the closed period months should be calculated and the volume added to the minimum slurry storage. As is good practice, farmers should prevent water from gutters or runoff from yards entering slurry stores.

When clean/dirty water enters a slurry store, it is then classed as slurry and must be held over for the closed period.

Many farmers who found themselves short on slurry storage used outwintering as a means of lessening their requirements. However, maximum stocking rates over the closed period have now been applied to farms seeking to outwinter stock.

Drystock farms with a stocking rate less than 130kg N/ha and dairy farms with a stocking rate not exceeding 85kg N/ha can avail of outwintering, with the storage requirements reduced in proportion to the percentage of stock outwintered.

Where stocking rates are above these thresholds, storage facilities are required for all stock on the farm, regardless if they are utilised.

Reports from tillage farmers are that straw is slow to leave yards, pointing to many farmers yet to purchase their winter straw requirements.

Table 1 charts the requirement of straw for each livestock type, as recommended by the Department of Agriculture, although many farmers will use significantly more than this.

Using a good-quality, chopped straw will have a greater absorption and will reduce straw requirements. A typical 4x4 round bale of straw weighs 150kg.

Sloping floors towards effluent channels to remove excess urine will also aid in keeping bedding drier for longer. Bedding should be topped up as necessary, with high traffic areas, such as along feed barriers, most prone to wetting. This can cause a buildup of bacteria, leading to scours in calves or foot ailments in sheep.