/api/v1/fertiliser

`GET /api/v1/fertiliser` — latest estimate per product with track record. Mounted by [`crate::gb`].

/api/v1/fertiliser/divergence

`GET /api/v1/fertiliser/divergence`: per-day forward-error time series for one or all grades. Shows how far the daily estimate was from the next weekly market print.

• product (query) — Product code to filter by: AN_UK, AN_IMPORT, UREA_GRANULAR, UAN, NITRATE_SULPHUR, DAP, TSP, MOP, POLYSULPHATE. Omit for every grade.
• days (query) — Lookback window in days, default 90. Clamped to the range 1 to 365; a larger value returns 365 days rather than an error.

/api/v1/fertiliser/estimates/history

`GET /api/v1/fertiliser/estimates/history?product=X` — recent estimate history for one product (the "nowcast line"), newest-first, capped at 400 rows (covers 13+ months at daily cadence; was 70, sized for the old weekly-only cadence). Mounted by [`crate::gb`].

• product (query, required) — Product code: AN_UK, AN_IMPORT, UREA_GRANULAR, UAN, NITRATE_SULPHUR, DAP, TSP, MOP, POLYSULPHATE

/api/v1/fertiliser/narrative

`GET /api/v1/fertiliser/narrative?product=AN_UK` - ranked market facts for the product's SEO narrative and authoritative display range. Both are COMPUTED here (`fertiliser_facts`); the marketplace only renders them. Empty `facts` and a null `display_range` are returned for an unknown/data-less product.

• product (query, required) — Product code: AN_UK, AN_IMPORT, UREA_GRANULAR, UAN, NITRATE_SULPHUR, DAP, TSP, MOP, POLYSULPHATE

/api/v1/fertiliser/official-index-comparison

`GET /api/v1/fertiliser/official-index-comparison?product=AN_UK`: rebased overlay of the daily forecast vs the official DEFRA index. Consistency + lead-time only; no accuracy percentage (spec R1). Mounted by [`crate::gb`].

• product (query, required) — Product code: AN_UK, AN_IMPORT, UREA_GRANULAR, UAN, NITRATE_SULPHUR, DAP, TSP, MOP, POLYSULPHATE

/api/v1/fertiliser/overview

`GET /api/v1/fertiliser/overview` - the market-wide weekly aggregate for the hub page (how many grades rose, the biggest mover). Aggregate market claim, computed here.

/api/v1/fertiliser/series

`GET /api/v1/fertiliser/series?product=AN_UK&cadence=weekly` — that product's curated AHDB price series (date + price + cadence), newest-first, capped at 70 prints (≈16 months of weekly — enough for a 1-year window plus a 1-year-ago comparison). `cadence` defaults to `weekly`; only `weekly` and `monthly` are accepted (any other value is a 400). Mounted by [`crate::gb`].

• product (query, required) — Product code: AN_UK, AN_IMPORT, UREA_GRANULAR, UAN, NITRATE_SULPHUR, DAP, TSP, MOP, POLYSULPHATE
• cadence (query) — Print cadence, `weekly` (default) or `monthly`. Any other value returns 400.