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NPB10 — Negative Phosphorus Balance 10% (Negativ fosforbalance 10%)

Summary

Targeted under-fertilization with phosphorus, reducing soil P content over time and thereby reducing P losses from all three pathways (erosion, macropore, matrix). The "10" refers to the intensity of the under-fertilization applied. Under-fertilizing by 10 kg P/ha/yr over 10 years reduces the soil P pool, which reduces all P transport mechanisms proportionally.

Eligibility

PotV(i,"NPB10") = Countcy(i) × IniPotV(i) / 5

N Effect

None as a standalone. Has N effects only in the combined measures NPB10_BZ10 and NPB10_BZ20.

P Effect

P_Effects_matrix(i,"NPB10")    = PotV(i,"NPB10") × matrix_ha(i) × 0.05
P_Effects_macropore(i,"NPB10") = macropore_field(i) × 0.05   [if PotV > 0]
P_Effects_erosion(i,"NPB10")   = erosion_field(i) × 0.05     [if PotV > 0]
P_Effects_Total = sum of above
The 0.05 factor reflects the 10% buffer covering ~5% of total P flux (accounting for landscape position and interception efficiency). ⚠️ The mapping from 10% coverage to 0.05 P reduction factor needs clarification.

Cost

CostM(i,"NPB10") = 50 DKK/ha/yr — very low. One of the cheapest P measures.

Mutual exclusions

Member of mem(j), pho(j). Mutually exclusive with NPB20 (can only choose one buffer intensity per field).

Notes

  • NPB10 vs NPB20: NPB20 has 4× the P effect (0.20 vs 0.05) but only 2× the cost (100 vs 50). NPB20 is typically more cost-effective per kg P.
  • The matrix P effect uses PotV as a multiplier (total ha), while macropore and erosion effects use field-total loss parameters. This asymmetry is intentional (matrix loss is per ha, while macropore/erosion are total field losses).
  • The 0.05 factor (5% reduction in each pathway) is a simplification of the catalog's quantity-based approach. The catalog quantifies effects as very small absolute numbers (0.1 kg P/ha/yr for erosion under 10 kg/ha underfertilization over 10 years), but the model expresses them as a fraction of the field's current P loss.

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 (0.05), cost: hard-coded in TargetEcon 2026.gms

Catalog source

SR379 — DCE Scientific Report no. 379 (Andersen et al., 2020): Chapter "Negativ fosforbalance (målrettet undergødskning med fosfor)" (p. 40–46). Authors: Gitte Holton Rubæk, Goswin Heckrath et al.

Mechanism: Reducing P application below crop offtake gradually depletes soil P content. Lower soil P reduces the driving force for P losses via all transport pathways (erosion, macropore, matrix). The measure addresses the source (soil P pool) rather than any specific transport route.

Target areas: Mineral (højbund) soils with risk of P loss — either erosion-prone or macropore/drain-loss areas with elevated soil P content. NOT suited for organic/lavbund soils (those are covered by Paludikultur and biomass removal).

Catalog effect (high-risk areas, 10 kg P/ha/yr underfertilization over 10 years): - Erosion pathway: 0.10 kg P/ha/yr - Macropore pathway: 0.05 kg P/ha/yr - Welfare-economic CE: 640 kr/kg P (erosion), 1,280 kr/kg P (macropore)

Larger dose (20 kg P/ha/yr, 20 years), high-risk areas: - Erosion: 0.44 kg P/ha/yr - Macropore: 0.22 kg P/ha/yr - Budget CE: 227 kr/kg P (erosion), 455 kr/kg P (macropore)

Model vs catalog mismatch: The catalog treats NPB as an absolute reduction in kg P/ha/yr dependent on the soil P starting level and duration. The model uses 0.05/0.20 as a proportional factor on existing P losses — a simplification that allows field-level targeting without requiring explicit soil P status data.

Cost in catalog: 5 kr/kg P in reduced P input (=50 kr/ha/yr for 10 kg P/ha underfertilization). This matches the model's 50 DKK/ha/yr cost for NPB10 almost exactly. ✅

Confidence: Not explicitly stated; the catalog notes weak Danish empirical data for dose-response and flags international evidence as the main basis. Implicit confidence ≈ *.

  • NPB20 — 20% under-fertilization; 4× P effect, 2× cost; usually more cost-effective
  • PPC — combined with NPB in PPC_NPB10 and PPC_NPB20 (synergy discount)
  • OT — combined with NPB in NPB10_OT and NPB20_OT
  • Combined measures
  • P loss pathways — NPB10 reduces all three pathways
  • P Reduction — equations for matrix, macropore, erosion effects
  • Cost concepts — fixed cost only (50 DKK/ha/yr)