Manure Storage Calculator: Slurry Pit and Manure Pad Sizing

Slurry pit and manure pad: storage needed for your herd

Pit volume = slurry produced per month × months of storage + rain falling on the uncovered area, plus a 10% freeboard. In French nitrate vulnerable zones, the order of 19 December 2011 requires 4 to 7.5 months of storage depending on species, time spent outdoors and zone. For 65 dairy cows and 30 heifers over 6 months, the tool finds about 895 m³ of pit and 130 m² of manure pad.

How the tool works

• Monthly output per head: dairy cow 2.2 m³ of slurry or 1.8 m³ of solid manure, suckler cow 1.5 and 1.5, heifer or young cattle 0.9 and 0.9, fattening pig 0.18 and 0.12, sow with piglets 0.55 and 0.35, ewe or goat 0.10 and 0.15.
• The slurry share you choose applies to slurry, the remainder to solid manure.
• Rain = annual rainfall ÷ 12 × months × uncovered area ÷ 1,000.
• Pit = (slurry × months + rain) × 1.10; manure pad = manure × months ÷ 2 m heap height.
• Nitrogen, phosphate (P₂O₅) and potash (K₂O) produced per year: for example 105, 42 and 110 kg per dairy cow, 45, 20 and 50 kg per heifer.

Worked example

65 dairy cows and 30 heifers, 6 months, 70% slurry, 250 m² uncovered, 800 mm of rain: slurry 119 m³/month, i.e. 714 m³ + 100 m³ of rain = 814 m³, 895 m³ with freeboard. Manure: 43.2 m³/month, 259 m³ over 6 months, 130 m² of pad. Nitrogen produced: 8,175 kg a year, so at least 48 ha of spreading land to stay within 170 kg of organic nitrogen per hectare.

Limits

Storage duration is an input: check the one that applies to your farm. Sows and ewes or goats each have their own head-count field. Some nitrogen references in the tool exceed the spreadable nitrogen set by the French order (68 kg for a suckler cow without calf, 17.4 kg for a sow on slats), and seepage from the manure pad is not counted. Any building project should be sized with an agricultural adviser.

Sources and dates: minimum storage periods (annex I) and the cap of 170 kg of livestock nitrogen per hectare of farmland: French order of 19 December 2011 on the national nitrates action programme, version in force since 10/02/2023, implementing Directive 91/676/EEC; per-head manure volumes and NPK contents in the tool are indicative values, not verified (checked 14/10/2026).

Frequently Asked Questions

How many months of slurry storage are required in a French nitrate vulnerable zone?

Annex I of the order of 19 December 2011 (version in force since 10/02/2023) sets periods by species, zone and time spent outdoors: 4 to 7 months for cattle, 7.5 months for pig slurry (type II fertiliser) and 7 months for pig solid manure. Enter the period that applies to your farm in the tool.

What pit volume do 65 dairy cows need?

With 70% of excreta as slurry, 30 heifers, 6 months of storage, 250 m² uncovered and 800 mm of rain a year, the tool calculates 895 m³ of usable volume, including 100 m³ of rainwater and a 10% freeboard.

What is the 170 kg of nitrogen per hectare cap?

In nitrate vulnerable zones, nitrogen from livestock manure spread each year must not exceed 170 kg per hectare of farmland, under the Nitrates Directive 91/676/EEC. Divide the nitrogen produced by 170 to estimate the minimum area: 8,175 kg require at least 48 ha.

Should rainwater be included in the pit volume?

Yes, for an uncovered pit. The tool adds annual rainfall ÷ 12 × months × open area: 800 mm on 250 m² over 6 months amounts to 100 m³. Covering the pit removes that volume.

Is this tool really free?

Yes, all tools on Kristools are 100% free and accessible without registration.

Is my data protected?

Yes. All processing is performed directly and securely inside your browser. No personal data is sent to our servers.