How Much Slurry Storage Do You Really Need for NVZ Rules in 2026?
Under NVZ regulations, most UK livestock farmers must have 5 months of slurry storage (October to March) if spreading is banned during the closed period. Getting this wrong can lead to heavy fines — but many tanks are either oversized or dangerously undersized.
This free calculator gives you accurate gross and available winter capacity in both m³ and UK gallons — automatically applying the 750 mm rainfall deduction for open tanks and standard 300 mm freeboard.
NVZ Slurry Storage Requirements — 2026
- Minimum storage period: 5 months for most farms in NVZs (6 months for pigs/poultry in some areas)
- Closed spreading period: 1 October to 1 March (grassland) or 1 April (tilled land)
- Rainfall deduction: 750 mm (0.75 m) must be subtracted from open tank capacity for winter availability
- Freeboard: Minimum 300 mm (0.3 m) below top of wall or 750 mm for earth-banked lagoons
- Covered tanks: No rainfall deduction required — increasing effective capacity significantly
Typical Slurry Production Rates
Dairy Cow
1.8–2.2 m³/month
Beef Cattle (>1yr)
1.0–1.4 m³/month
Pig (finishing)
0.2–0.3 m³/month
Laying Hen
0.015–0.02 m³/month
Example Calculations
- Rectangular lagoon: 30 m × 20 m × 4 m deep, uncovered, 0.3 m freeboard — Gross 2,400 m³ — Available ~1,900 m³ (after 500 m³ rainfall deduction)
- Circular steel store: 22 m diameter × 4.5 m deep, covered — Gross ~1,710 m³ — Available 1,710 m³ (no rainfall loss)
- 100 dairy cow herd: ~200 m³/month × 5 months = 1,000 m³ minimum required
Tips for NVZ Compliance & Cost Savings
- Cover existing tanks — eliminates rainfall deduction and can add 20–30% effective capacity
- Separate clean water — roof gutters and yard drainage prevent unnecessary dilution
- Accurate records — measure actual depths regularly to prove compliance
- Plan expansions carefully — slightly oversized stores save money long-term vs multiple small ones
- Check grants — Slurry Infrastructure Grant still available in many regions for new/upgraded storage
Frequently Asked Questions
- Do I need 5 or 6 months storage?
- Most cattle/sheep farms need 5 months. Pig/poultry farms often need 6 months — check your NVZ designation.
- Is the 750 mm rainfall deduction still required?
- Yes — for all uncovered stores. Covering removes this requirement completely.
- What about weeping wall stores?
- They count as uncovered — full rainfall deduction applies.
- Can I use this for SSAFO compliance too?
- Yes — the calculator includes standard freeboard requirements used in both NVZ and SSAFO regulations.