NZ regenerative/permaculture vegetable irrigation requirement (2026 web synthesis)
Resolves RT_259 — the food↔water coupling figure
Applied irrigation (what the grower must supply = crop demand − effective rainfall, reduced by water-conserving practice), NOT total crop ET. Lands ~2.0 ML/ha/yr (200 mm/yr) national default ≈ 45% of the conventional 4.5 ML/ha that D_001 forbids — but the figure is regionally dominated (wet-west <1.0; dry-east 2.5–3.0) and low–medium confidence (a built-up estimate; no NZ peer-reviewed permaculture-irrigation figure exists). AI-prepared (WebSearch + Consensus) → data_quality medium.
Summary
The model’s food domain is regenerative-only (D_001), so the conventional ~4.5 ML/ha/yr market-garden irrigation figure cannot be used. There is no NZ-specific peer-reviewed “permaculture applied-irrigation” figure — so the defensible number is built up from conventional NZ vegetable irrigation depths, minus the quantified reductions water-conserving practices deliver, with a floor set by the NZ summer soil-moisture deficit. Stacking those gives ~1.5–3.0 ML/ha/yr (150–300 mm), point estimate ~2.0 ML/ha/yr (≈45% of conventional). The reduction is real but bounded: it comes from cutting evaporative and convenience losses (mulch, high SOM, ground cover, swales), not from reducing the plants’ transpiration, which is fixed by yield and climate. The single biggest driver is the wet-west/dry-east gradient — and, awkwardly, the regenerative saving is largest where the climate is already kind and smallest exactly where the garden actually needs water (the dry east, where a 300–500 mm summer PED dominates). Two popular over-claims are corrected: mulch’s “70% saving” is a cut to the evaporation slice (~15–30% off seasonal irrigation in practice), and GROW BIOINTENSIVE’s “88% less water” is per-pound-of-food advocacy data, not area-based, and cannot be transferred to ML/ha.
Key claims
- claim: "Applied-irrigation figure for a regenerative/permaculture NZ vegetable system (RT_259). No NZ-specific peer-reviewed figure exists; the defensible number is BUILT UP from conventional NZ veg irrigation depths (potatoes ~300–400 mm/season, onions ~350–400 mm; general veg ~25–30 mm/week → ~500–600 mm seasonal DEMAND of which rain meets part) minus the quantified regenerative reductions. Result: ~1.5–3.0 ML/ha/yr (150–300 mm applied), POINT ESTIMATE ~2.0 ML/ha/yr (200 mm ≈ 200 L/m²/yr) ≈ 45% of the conventional 4.5 ML/ha. LOW–MEDIUM confidence. It is region-dominated: wet-west (Westland/Taranaki) <1.0 ML/ha/yr (may approach rain-fed); dry-east (Canterbury/Marlborough/Hawke's Bay/Central Otago) 2.5–3.0. Suggested model treatment: 2.0 national default with a regional PED multiplier (~0.4× wet-west, ~1.4× dry-east) — a modelling SUGGESTION, not a measured value."
source_location: "Watercare garden guidance (25–30 mm/wk); Tasmania DNRE annual-crops factsheet (potato/onion mm); Agronomy Society NZ (potato PAW); built-up estimate"
- claim: "Water-conserving mechanisms — what they actually reduce, and two over-claims corrected. MULCH (best-evidenced) cuts the SOIL-EVAPORATION slice only: peer-reviewed straw-mulch field data show daily soil evaporation down 25–41% (Wang 2018) and the effect concentrates in early crop stages, diminishing after canopy closure (Ramos 2024, 58-study review); the popular NZ '~70% evaporation reduction' (Watercare) therefore translates to only ~15–30% off SEASONAL IRRIGATION, not 70% (interpretation, not a cited figure). HIGH SOIL ORGANIC MATTER adds ~15–20 mm plant-available water per metre depth per +1% SOM (~150,000 L/ha; texture-dependent) — it buffers between events / reduces irrigation FREQUENCY, not total seasonal demand. SWALES/keyline/contour raise EFFECTIVE RAINFALL (better modelled as extra rainwater capture than as an irrigation discount). GROW BIOINTENSIVE's '3–8× less water / 88% less per pound of vegetable' (Jeavons/Ecology Action) is PER-UNIT-OF-FOOD advocacy driven by yield density, self-reported, no independent peer-reviewed replication — it CANNOT be transferred to an area-based ML/ha figure."
source_location: "Wang et al. 2018 Field Crops Research; Ramos et al. 2024 Irrigation Science; Bekele et al. 2023 Hydrology; EDIS/Univ. Florida + NFU (SOM); EcoFarming Daily Jeavons interview + Wikipedia biointensive (critique)"
- claim: "NZ reality check — permaculture reduces but cannot eliminate summer irrigation in the dry east. NIWA's Potential Evapotranspiration Deficit (PED, the water rain/irrigation must supply to keep growth unconstrained) averages ~300–500 mm/yr in the driest NZ areas (NIWA/MfE); the Nelson/Tasman summer soil-moisture deficit ~317 mm sits mid-band, with Marlborough/Canterbury/Hawke's Bay/Central Otago drier and severe droughts projected to increase. The wet-west/dry-east gradient is the single biggest driver of the irrigation figure, and the regenerative reduction is largest where irrigation matters least (wet-west) and smallest where it matters most (dry-east) — practice trims evaporative/convenience losses but cannot remove the climatic deficit. A national model should scale the figure by regional PED, not apply 2.0 everywhere."
source_location: "NIWA/MfE Climate Change Projections (PED 300–500 mm); NIWA VCSN; project file (Nelson/Tasman SMD 317 mm, OT_030)"Neobiome Intelligence relevance
Resolves RT_259 — supplies the veg→water coupling figure (food slice). The food garden draws irrigation water on top of household demand: veg_irrigation_yr ≈ food_land_ha × permaculture_irrigation_ML_ha_yr, which adds to the water-domain demand the D22 cascade must meet (and so can push a community toward a water backstop). Under D_001 the conventional 4.5 ML/ha (CR_018) is explicitly not used; CR_033 supplies the regenerative figure ~2.0 ML/ha/yr.
Design implication: the figure is region-dominated, so a flat national 2.0 understates dry-east draw and overstates wet-west. The honest wiring is a national default × regional PED multiplier (or a regional irrigation column like rainfall_mm), so veg-garden water tracks the wet-west/dry-east gradient. The figure is low–medium confidence — flag every output that depends on it, and prefer the regional treatment.
Retrieval provenance
Values AI-extracted / built-up, unverified until spot-checked. Compiled by an agent using WebSearch + Consensus (Perplexity MCP unavailable). The headline 2.0 ML/ha/yr is a derived build-up, not a measured value; the supporting mechanism evidence (mulch/SOM/PED) is peer-reviewed and sourced. The “~15–30% off seasonal irrigation” and the regional multipliers (0.4×/1.4×) are interpretations/modelling suggestions, not cited figures. Exact brief in the _retrieval.md sidecar.
Research targets
Documents to retrieve
- A primary NZ measurement — metered tank/bore draw per bed-area per season from a regenerative grower — or an IrriCalc/Aqualinc run parameterised for a mulched, high-SOM bed in a target region. Would lift the figure from built-up/low–med to a measured anchor (RT_263).
Research gaps
- A regional PED / irrigation-multiplier layer (NIWA VCSN PED by region) to drive the wet-west/dry-east scaling the figure demands — the data behind a regional
irrigation_mmcolumn (RT_264).
Connections
Links to
Sources (1): CR_018
Referenced by
Sources (3): OT_108 · OT_112 · OT_191
EDT domains (2): D02: Smart Food Systems & Agriculture · D03: Water, Waste & Circular Systems