Compost Application Rate – N Release

Only part of compost nitrogen feeds the first crop — the mineralization or utilization rule. Standard planning assumes about 50% of total N is available in year one for manure-based composts, with the remainder releasing over 2–3 years. Worked example: compost testing 1.5% total N (15 kg/t) against a vegetable crop needing 120 kg N/ha: at 50% availability each tonne supplies 7.5 kg N, so the rate is 120 ÷ 7.5 = 16 t/ha (6.5 t/acre ≈ 7.2 short tons). Phosphate and potash ride along: the same compost at 0.9% P₂O₅ and 1.0% K₂O adds 144 kg P₂O₅ and 160 kg K₂O — usually enough for the rotation, so credit them against future fertilizer.

1. 1

   Step 1

   Enter the crop’s N requirement (kg/ha or lb/acre).

2. 2

   Step 2

   Enter compost total N % from the analysis sheet.

3. 3

   Step 3

   Set year-1 availability (default 50%).

4. 4

   Step 4

   Read t/ha and tons/acre plus P-K carried by the compost.

• 1

  Ask suppliers for an analysis: N-P-K, moisture, C:N, salts

• 2

  Year-2 residual credit ≈ 15–20% of total N

• 3

  Surface-apply and water in; incorporation loses less NH₃ from manure

• 4

  Heavy rates build P — track soil tests to avoid runoff

• Counting 100% of compost N in year one and shorting the crop

• Ignoring salinity above 30–40 t/ha rates

• Spreading fresh manure where compost was budgeted — different availability

• Not crediting residual N in years 2–3 after repeated applications