Skip to content

NPB20 — Negative Phosphorus Balance 20% (Negativ fosforbalance 20%)

Summary

A more intensive version of NPB10: stronger under-fertilization, depleting soil P more rapidly and achieving 4× the P effect at 2× the cost. Corresponds to approximately 20 kg P/ha/yr under-fertilization sustained over 20 years.

Eligibility

PotV(i,"NPB20") = Countcy(i) × IniPotV(i) / 5

P Effect

All factors are 0.20 (vs 0.05 for NPB10): 

P_Effects_matrix(i,"NPB20")    = PotV × matrix_ha(i) × 0.20
P_Effects_macropore(i,"NPB20") = macropore_field(i) × 0.20
P_Effects_erosion(i,"NPB20")   = erosion_field(i) × 0.20

Cost

CostM(i,"NPB20") = 100 DKK/ha/yr

Notes

NPB20 is more cost-effective than NPB10 per kg P reduced (4× effect, 2× cost). The model will typically prefer NPB20 unless NPB10 is in a combined measure with BZ that makes the package cheaper.

Data sources

  • Erosion P loss (erosion_field(i)): erosion_field.inc
  • Macropore P loss (macropore_field(i)): macropore_field.inc
  • Matrix P loss per ha (matrix_ha(i)): matrix_ha.inc
  • P effect factors (0.20), cost: hard-coded in TargetEcon 2026.gms

Catalog source

SR379 (Andersen et al., 2020): Same chapter as NPB10 — "Negativ fosforbalance" (p. 40–46). The catalog presents two scenarios: - 10 kg P/ha/yr under-fertilization × 10 years → corresponds to NPB10 - 20 kg P/ha/yr under-fertilization × 20 years → corresponds to NPB20 (0.44 kg P/ha/yr erosion, 0.22 kg P/ha/yr macropore in high-risk areas)

The non-linear relationship (4× effect for 2× intensity × 2× duration) reflects both the dose and the time needed to reduce soil P to where losses are materially lower. Model cost (100 DKK/ha/yr) matches 5 kr/kg P × 20 kg/ha. ✅

See NPB10 for full catalog discussion.

  • NPB10 — 10% variant; see for full catalog notes; 5% reduction factor
  • PPC — erosion-targeting companion; combined as PPC_NPB20
  • OT — tillage-based companion; combined as NPB20_OT
  • Combined measures
  • P loss pathways — NPB20 reduces all three pathways
  • P Reduction — equations for all three NPB20 effects
  • Cost concepts — fixed cost only (100 DKK/ha/yr)