N10 — Nitrogen Norm Reduction 10% (N-normsreduktion 10%)

Summary

A 10% mandatory reduction in the N fertilization norm. Farmers apply 10% less nitrogen than the current legal maximum. Reduces N leaching proportionally to the field's baseline N application.

Eligibility

PotV(i,"N10") = Countcy(i) × IniPotV(i) / 5 — applicable to all fields with eligible crops.

N Effect

NEffM(i,"N10") = 0.1 × 0.18 × Nhan(i)   [kg N/ha/yr]

- 0.1 = 10% norm reduction - 0.18 = fraction of applied N that leaches to water (18% leaching coefficient) - Nhan(i) = field-specific N application norm (kg N/ha/yr) from Nhan_i2.inc

Effect is field-specific and higher for intensively fertilized fields.

P Effect

None.

Cost

CostM(i,"N10") = 44.5 DKK/ha/yr — low flat rate. This represents compensation for reduced yield from lower N application.

Retention type

TR (Total retention)

Mutual exclusions

Member of mem(j). N10 and N20 are mutually exclusive (only one norm reduction level per field).

Data sources

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

Catalog source

DCA Rapport nr. 174 (Eriksen et al., 2020): Chapter "Reduceret tilførsel af mineralsk kvælstofgødning" (p. 221–241). Authors: Christen Duus Børgesen, Peter Sørensen, Gitte Blicher-Mathiesen et al.

N leaching model: The catalog uses the NLES5 empirical N leaching model to quantify marginal leaching — the fraction of each additional kg N/ha applied that reaches the root zone leachate. Key results (Tabel 2, p. 225):

Soil type	Marginal leaching (% of applied N)	Notes
JB7 (clay, wet)	21%	Wet climate conditions
JB7 (clay, avg)	17%	Average conditions
JB1 (sand, wet)	31%	Wet climate conditions
JB1 (sand, avg)	27%	Average conditions

The model uses a flat 18% leaching coefficient (0.18) — this is in the center of the catalog's clay-soil range and slightly below the sand range. The simplification is consistent with a national average but loses some spatial resolution.

Budget cost from catalog: 2–69 DKK/kg N for 10% norm reduction (very wide range; sand at low cost, clay at high cost). The model's flat 44.5 DKK/ha/yr maps to ~9–22 DKK/kg N at typical N-application rates — consistent with the catalog's lower range.

Note on the 18% coefficient: The catalog shows marginal leaching is crop- and soil-dependent and varies significantly by year (wet vs. dry). The 18% is a pragmatic simplification; actual marginal leaching ranges from ~14% (clay, winter wheat) to ~33% (sand, spring barley, wet year). This means the model may under-estimate effects on sandy soils and over-estimate on clay soils.

Notes

• N10 and N20 are among the cheapest measures per kg N reduction, but their effectiveness scales with Nhan(i) — most effective on highly-fertilized fields.
• Cost-effectiveness heavily dependent on TotRet(i) — low retention catchments benefit most.
• ✅ The 18% leaching coefficient is broadly consistent with the NLES5 model but is a national average simplification.

Related pages

• N20 — 20% reduction; double effect, ~4× cost (non-linear yield response)
• Retention types — N10 uses TR (total retention)
• Cost concepts — fixed cost only (44.5 DKK/ha/yr); among cheapest measures
• N Reduction — N10 in TR set; NEffM depends on Nhan(i)