Natural Resources Extension Program

1. Calculate amount of organic N in manure per ton:

lb total N – (lb ammonium N + lb nitrate N) = lb organic N

21 – (8 + 0) = 13 lb organic N/ton

2. Calculate amount of organic N in manure available first year:

lb organic N/ton x mineralization factor* = available organic N/ton 
(* solid with bedding, see table)

13 x 0.25 = 3.25 lb available organic N/ton first year

3. Calculate amount of plant-available N in manure:

Surface application of manure (assumes 1/3 of ammonium N lost by volatilization)

Available organic N + (Ammonium N x 0.66) + Nitrate N = lb plant-available N/ton

3.25 + (8 x 0.66) + 0 = 8.53 lb available N/ton

4. Account for residual manure application if available.

No manure has been applied previously.

5. Annual manure applications if based on amount of N required by crop:

Adjusted N required divided by Available N/ton

160 divided by 8.53 lb available N/ton = 18.8 tons/ac to meet N crop need

6. Annual manure application if based on amount of P₂O₅ required by crop:

P₂O₅ required by crop divided by lb P₂O₅ = tons of manure/ac

50 lb divided by 18 = 2.8 tons of manure/ac to meet P₂O₅ crop need

7. Annual manure application if based on amount of K₂O required by crop:

K₂O required by crop divided by lb K₂O = tons of manure/ac

75 lb divided by 26 = 2.9 tons of manure/ac to meet K₂O crop need