CCS — Catch Crops (Spring / Efterafgrøder, forår)¶

Summary¶

Sowing of catch crops after a spring main crop (e.g. spring barley). The catch crop takes up residual soil nitrogen over autumn and winter, reducing N leaching to groundwater and streams.

Eligibility / Potential area¶

PotV(i,"CCS") = Sum(cy, sc(i,cy)) / 5

Where sc(i,cy) = IniPotV(i) if the crop in year cy is a spring crop (crop codes 10, 22, 24), else 0. Average over 5 crop years. Fields with no spring crops in the rotation have PotV = 0.

N Effect¶

NEffM(i,"CCS"):
  livestock ≥ 0.8, soil < 5 (sandy):  45 kg N/ha/yr
  livestock ≥ 0.8, soil ≥ 5 (clay):   24 kg N/ha/yr
  livestock < 0.8, soil < 5 (sandy):   32 kg N/ha/yr
  livestock < 0.8, soil ≥ 5 (clay):    12 kg N/ha/yr

Higher livestock → higher N application → higher residual N → higher catch crop effect. Sandy soils → higher leaching → higher catch crop effect.

P Effect¶

None. CCS is not in the P effects matrices.

Cost¶

CostM(i,"CCS"):
  soil < 5, livestock < 0.8:   384 DKK/ha/yr
  soil < 5, livestock ≥ 0.8:   315 DKK/ha/yr
  soil ≥ 5, livestock < 0.8:   396 DKK/ha/yr
  soil ≥ 5, livestock ≥ 0.8:   288 DKK/ha/yr

Pure implementation cost — no opportunity cost component (catch crops are sown after harvest).

Retention type¶

TR (Total retention) — the N reduction passes through the full landscape retention factor (1 − TotRet(i)/100) before reaching the coast.

Mutual exclusions¶

Member of mem(j) — cannot be combined with any other mem measure on the same field.

Data sources¶

Cost and N effect values: hard-coded in TargetEcon 2026.gms
Spring crop identification (MarkAccess(i,cy)): MarkAccess2.inc

Catalog source¶

DCA Rapport nr. 174 (Eriksen et al., 2020): "Virkemidler til reduktion af kvælstofbelastningen af vandmiljøet", Chapter "Efterafgrøder" (p. 33–58).

The catalog confirms all four NEffM values from the model (Table 2, p.40):

Soil type	Organic N input	N effect (kg N/ha/yr)
Sandy (JB1–4)	< 80 kg N/ha	32
Sandy (JB1–4)	≥ 80 kg N/ha	45
Clay (JB5+)	< 80 kg N/ha	12
Clay (JB5+)	≥ 80 kg N/ha	24

Confidence level: *** (high — based on ~112 paired field experiments and lysimeter data)

Budget cost from catalog: 7–167 DKK/kg N reduced; welfare economic: 9–214 DKK/kg N. The wide range reflects variation in soil type, crop rotation, and leaching potential.

Mechanism: Catch crops absorb residual soil N after harvest of the main crop, preventing leaching during the autumn–winter period. Effect assumes spring ploughing on sandy soils, autumn ploughing on clay soils (consistent with regulations).

No timing advantage: Effects cannot be directed to specific months of the year.

Overlap note: Catch crops overlap with other field-level measures — the catalog explicitly states effects are not additive when combined with drain measures such as IBZ or wetlands (as less N reaches the drain).

Notes & open questions¶

CCW (winter catch crops) has the same N effect values but very different costs — CCW is much more expensive because it replaces a winter cash crop.
No P effect for CCS. It is a purely N-targeted measure.
The CCS/CCW distinction is not explicit in the catalog (both are "efterafgrøder"); the cost difference in the model reflects the opportunity cost of replacing a winter crop with a catch crop.

Scenario appearances¶

To be filled as scenarios are documented.

CCW — winter counterpart; same N effect, higher cost (replaces cash crop)
Retention types — CCS uses TR (total retention)
Cost concepts — fixed cost only; no prodcost component
N Reduction — CCS appears in TR set in core equation