N20 — Nitrogen Norm Reduction 20% (N-normsreduktion 20%)¶

Summary¶

A 20% reduction in N fertilization norm. Double the effect of N10, with proportionally higher cost.

Eligibility¶

PotV(i,"N20") = Countcy(i) × IniPotV(i) / 5

N Effect¶

NEffM(i,"N20") = 0.2 × 0.18 × Nhan(i) — exactly double N10.

P Effect¶

None.

Cost¶

CostM(i,"N20") = 178 DKK/ha/yr — exactly 4× the N10 cost (non-linear: doubling the reduction costs 4× as much, reflecting yield response curves).

Retention type¶

TR (Total retention)

Mutual exclusions¶

Member of mem(j). Mutually exclusive with N10.

Data sources¶

N application norm (Nhan(i)): Nhan_i2.inc
Leaching coefficient (0.18), cost, eligibility: hard-coded in TargetEcon 2026.gms

Catalog source¶

See N10 — same chapter: DCA Rapport nr. 174, Chapter "Reduceret tilførsel af mineralsk kvælstofgødning" (p. 221–241).

N effect for 20% reduction: The catalog confirms that the marginal leaching rate applies to the full 20% reduction — so the N effect is approximately double N10 (consistent with the model). At 10% reduction, the economic loss for winter wheat (Tabel 4, p. 233) is 59 DKK/ha; at 20% reduction it is 234 DKK/ha — reflecting a non-linear yield response curve (more than 4× cost for 2× N reduction).

Budget cost from catalog: 3–138 DKK/kg N for 20% norm reduction; welfare: 4–177 DKK/kg N. The high upper end reflects intensive farms where 20% reduction severely impacts yields.

Notes¶

Cost per kg N (before retention) is approximately 178 / (0.2×0.18×Nhan) vs 44.5 / (0.1×0.18×Nhan) = 2× as expensive per kg N as N10. The non-linearity in costs reflects the non-linear yield response curve confirmed by the catalog: reducing N by 20% costs approximately 4× as much as 10% (not 2×), because yields drop non-linearly as N is cut.
The catalog uses NREMO (N Response Model) — a sophisticated yield-response model calibrated on Landsforsøg data from 1992–2018.

N10 — 10% reduction; half the effect, quarter the cost
Retention types — N20 uses TR (total retention)
Cost concepts — fixed cost only (178 DKK/ha/yr); non-linear cost vs N10
N Reduction — N20 in TR set