Question 1

What is the difference between total N and available N in manure?

Accepted Answer

Total N is all the nitrogen in the manure. Available N (readily available N) is the fraction the crop can use in the year of application — typically 20–30% of total N for cattle FYM surface spread. The remainder is slowly released over subsequent seasons as organic matter breaks down. RB209 available N values are credited against manufactured fertiliser requirements.

Question 2

How much nitrogen is in 1 tonne of cattle FYM?

Accepted Answer

Cattle FYM typically contains around 6 kg total N per tonne, with approximately 1.5 kg available N per tonne (around 25% availability for surface-spread solid manure). Actual content varies significantly with feed ration, straw bedding rate, storage conditions and manure age. Laboratory analysis gives the most reliable figures for precise planning.

Question 3

Does FYM nitrogen count towards the NVZ 170 kg N/ha limit?

Accepted Answer

Yes. Under the UK Nitrates Regulations, the 170 kg N/ha limit applies to total nitrogen from all organic manure sources — FYM, slurry, compost, digestate and poultry litter. It is the total N figure (not the available fraction) that counts towards this limit. Manufactured fertiliser N is not included in the 170 kg organic manure cap.

Question 4

What is the nitrogen content of poultry litter?

Accepted Answer

Broiler litter is one of the richest manures: typically 28–35 kg total N per tonne with 60–70% available in the year of application. Layer manure (solid) runs around 15–20 kg total N/t. High nutrient content means application rates need careful calculation to avoid exceeding crop N requirements or the NVZ limit.

Question 5

How do I convert manure application from m³ to tonnes?

Accepted Answer

Multiply the volume (m³) by the bulk density (t/m³). Cattle FYM typically has a bulk density of 0.7–0.9 t/m³, so 50 m³ at 0.85 t/m³ = 42.5 tonnes. The calculator handles this automatically — enter m³ in the Total Application field and set your bulk density in the Manure Type section above.

Question 6

When should I apply FYM for the best nitrogen benefit?

Accepted Answer

Late winter or early spring applications (February–March on growing crops) maximise nitrogen availability by minimising leaching and volatilisation losses. Autumn applications to bare soil in NVZ areas are restricted or prohibited for most solid manures under the Nitrates Action Programme. Always check your NVZ closed period rules before spreading.

Question 7

Can I reduce my fertiliser application if I have spread manure?

Accepted Answer

Yes — the available N from manure is credited against the crop N requirement. For example, cattle FYM at 25 t/ha delivering 1.5 kg available N/t = 37.5 kg available N/ha, which can be deducted from your manufactured N. Use the AgriOps Crop Nitrogen Calculator and enter your available organic N to see the adjusted fertiliser requirement.

Question 8

How accurate are the RB209 average manure N values?

Accepted Answer

RB209 values are population averages — individual batches can vary considerably, particularly for poultry litter and pig slurry where diet and management have a large effect. AHDB recommend laboratory analysis for high-value decisions or if you are applying close to the NVZ limit. Quick-test ammonia kits are also available for field estimation of ammonium-N.

Manure Type	Total N	Avail N	Total P₂O₅	Total K₂O
Cattle FYM	6	1.5	3.5	8
Pig FYM	7	2.5	7	5
Sheep FYM	6.5	2	3	5
Horse Manure	7	1.5	3.5	5
Broiler Litter	30	18	25	18
Layer Manure (solid)	16	10	15	9
Mushroom Compost	10	4	10	10

Manure Nutrient Calculator

Manure Type & Nutrients

RB209 Manure Nutrient Reference

Frequently Asked Questions