Calculating 5 month slurry production
How cow production levels may be used to achieve the 5 month storage capacity requirement.
This is an idea that a fieldsman had when he was facing a situation where there was nearly but not quite 5 months slurry storage on the farm. Most people, as he did, use the herd average to calculate the slurry production per cow. For the sake of the example, the herd average was 6,300 litre and this meant the store was a few cubic metres short of 5 months capacity.
Realising that an average is made up of a range of individual production levels he and the farmer separated the herd into the NVZ calculation categories:
| Dairy Cows up to 6,000 l | slurry = 1.26 m3/month | e.g. 50 cows |
| Dairy Cows 6,000 - 9,000 l | slurry = 1.59 m3/month | 150 cows |
| Dairy Cows over 9,000 l | slurry = 1.92 m3/month | none of the herd |
A reduction of 50 cows * 0.33 m3/mth * 5 = 82.5 m3 over the 5 month storage period.
Enough to lower the slurry production value below the 5 month capacity of the slurry store. Everyone was happy.
A similar approach may also be taken to help drop below the N farm limit for organic Nitrogen.
A couple of provisos for the adviser:
Do the simple calculation first and if the herd average is middle of the range (7-8k litres) it is unlikely to significantly affect the outcome.
The calculation may look good but in an inspection the herd records may be asked for as supporting evidence. Do not start with the outcome and work backwards.
If the calculation is within a few cubes of capacity it does not leave much scope for herd production improvements. Though this solution will provide some thinking and planning time.
Additional note: Feedback from original publication suggested that some EA inspectors will accept these calculations, others will insist on a herd average calculation.
