[
  {
    "effect_size": 96.0,
    "effect_unit": "% (kg/m² per cycle vs FAO field mean)",
    "ci_lower": null,
    "ci_upper": null,
    "conditions": "121 papers, 979 observations, 29 countries. CEA mean 3.68 kg/m² vs FAO field 1.88 kg/m². Vertical stacked systems 6.88 kg/m². Greenhouse subset 5.11 kg/m² (n=415); indoor CEA rooms 2.65 kg/m² (n=508). Iceberg 7.45 kg/m² (n=41); looseleaf 2.58 kg/m² (n=266). Mean CEA cycle ~40 d vs field 60–120 d.",
    "study_count": 121,
    "comparison_count": 979,
    "source_url": "https://doi.org/10.3390/plants12142623",
    "potential_yield_effect": 96.0,
    "geography": "Global CEA vs FAO field benchmark",
    "intervention": "Greenhouse, polytunnel, or vertical/indoor CEA",
    "comparator": "FAO field lettuce yield 2009–2022",
    "dose": "",
    "dose_unit": "",
    "limitations": "Per-cycle kg/m², not annual and not profit. Vertical 6.88 kg/m² is stacked area; energy cost can erase the yield advantage.",
    "source_year": 2023,
    "doi": "10.3390/plants12142623",
    "baseline": "",
    "factor_id": "lettuce-cea-vs-field-meta",
    "crop_id": "lettuce",
    "factor": "Controlled-environment production versus field (system choice)",
    "factor_category": "Crop management",
    "direction": "positive",
    "effect_type": "yield_gain",
    "evidence_type": "meta_analysis",
    "evidence_strength": "High",
    "prairie_relevance": "moderate",
    "source_title": "Let-Us Investigate; A Meta-Analysis of Influencing Factors on Lettuce Crop Yields within Controlled-Environment Agriculture Systems (Gargaro, Murphy & Harris 2023)",
    "notes": "Dominant CEA yield factors in the meta-analysis: cultivar, season, nutrient-delivery method, lighting type. Faster cycles raise annual kg/m² more than the per-cycle ratio. Energy and GWP are higher in CEA (see Verteramo Chiu et al. 2024 J. Cleaner Prod. 10.1016/j.jclepro.2024.143142)."
  },
  {
    "effect_size": 0.9,
    "effect_unit": "% FW per 1% DLI ('Rex')",
    "ci_lower": null,
    "ci_upper": null,
    "conditions": "Indoor hydroponic lettuce 'Rex' and 'Rouxai'. DLI 6.9–15.6 mol m⁻² d⁻¹ via PPFD 120–270 µmol m⁻² s⁻¹ and photoperiods 16–24 h. Fresh and dry mass, leaf width and number, and chlorophyll increased with DLI. At 15.6 mol, lower PPFD + longer photoperiod beat higher PPFD + shorter day. ~0.9% ('Rex') and ~0.7% ('Rouxai') fresh-weight gain per 1% DLI increase.",
    "study_count": 1,
    "comparison_count": null,
    "source_url": "https://doi.org/10.1016/j.scienta.2020.109565",
    "potential_yield_effect": null,
    "geography": "Indoor hydroponic growth room (Michigan State)",
    "intervention": "Higher DLI (via PPFD and/or photoperiod)",
    "comparator": "Lower DLI in the same range",
    "dose": "",
    "dose_unit": "",
    "limitations": "Indoor sole-source lighting, not a glasshouse with sunlight. Tipburn risk rises with DLI unless airflow is managed.",
    "source_year": 2020,
    "doi": "10.1016/j.scienta.2020.109565",
    "baseline": "",
    "factor_id": "lettuce-dli-kelly-2020",
    "crop_id": "lettuce",
    "factor": "Daily light integral (DLI) 6.9 to 15.6 mol/m²/d",
    "factor_category": "Light",
    "direction": "positive",
    "effect_type": "dose_response",
    "evidence_type": "greenhouse_trial",
    "evidence_strength": "High",
    "prairie_relevance": "high",
    "source_title": "Promotion of lettuce growth under an increasing daily light integral depends on the combination of the photosynthetic photon flux density and photoperiod (Kelly, Choe, Meng & Runkle 2020)",
    "notes": "Prairie winter sunlight is often well below 12 mol/m²/d inside plastic houses, so this dose-response is the lighting investment case. Doubling DLI 10→20 mol can nearly double yield but raises tipburn and electricity (Produce Grower summary of the same lab)."
  },
  {
    "effect_size": 2.4,
    "effect_unit": "× edible g/kWh (LED/HPS, lowest of 3 harvests)",
    "ci_lower": null,
    "ci_upper": null,
    "conditions": "Greenhouse hydroponic lettuce, 13 cultivars, target DLI 17 mol m⁻² d⁻¹, LED 20% blue / 80% red vs HPS. LED produced 2.4–3.1 times as much edible mass per estimated kWh as HPS across three harvests.",
    "study_count": 1,
    "comparison_count": null,
    "source_url": "https://doi.org/10.3390/horticulturae6010007",
    "potential_yield_effect": null,
    "geography": "Greenhouse hydroponic lettuce",
    "intervention": "LED supplemental lighting at matched DLI",
    "comparator": "HPS at the same target DLI",
    "dose": "",
    "dose_unit": "",
    "limitations": "Biomass/kWh, not a higher yield at unlimited power. Fixture capital is extra.",
    "source_year": 2020,
    "doi": "10.3390/horticulturae6010007",
    "baseline": "",
    "factor_id": "lettuce-led-vs-hps-efficacy",
    "crop_id": "lettuce",
    "factor": "LED versus HPS supplemental lighting (biomass per kWh)",
    "factor_category": "Light",
    "direction": "positive",
    "effect_type": "other",
    "evidence_type": "greenhouse_trial",
    "evidence_strength": "Moderate",
    "prairie_relevance": "high",
    "source_title": "Quality, Yield, and Biomass Efficacy of Several Hydroponic Lettuce Cultivars in Response to High Pressure Sodium Lights or Light Emitting Diodes (2020)",
    "notes": "This is an energy-efficiency / profit factor more than a yield factor: matched DLI, more grams per kWh. Relevant where Alberta electricity or generator fuel is the binding constraint."
  },
  {
    "effect_size": 7.45,
    "effect_unit": "kg/m² iceberg mean (vs 2.58 looseleaf)",
    "ci_lower": null,
    "ci_upper": null,
    "conditions": "Within the Gargaro et al. 2023 CEA meta-analysis, iceberg averaged 7.45 kg/m² (n=41) versus looseleaf 2.58 kg/m² (n=266). Cultivar was one of the four strongest yield factors (with season, nutrient delivery, and lighting type).",
    "study_count": 121,
    "comparison_count": null,
    "source_url": "https://doi.org/10.3390/plants12142623",
    "potential_yield_effect": 7.45,
    "geography": "Global CEA",
    "intervention": "Iceberg-type cultivar",
    "comparator": "Looseleaf-type cultivar",
    "dose": "",
    "dose_unit": "",
    "limitations": "Subgroup means mix systems and cycle lengths. Price per kg differs by type, so kg/m² is not profit.",
    "source_year": 2023,
    "doi": "10.3390/plants12142623",
    "baseline": "",
    "factor_id": "lettuce-cultivar-cea-meta",
    "crop_id": "lettuce",
    "factor": "Cultivar choice inside CEA (iceberg vs looseleaf)",
    "factor_category": "Genetics",
    "direction": "positive",
    "effect_type": "yield_gain",
    "evidence_type": "meta_analysis",
    "evidence_strength": "Moderate",
    "prairie_relevance": "moderate",
    "source_title": "Let-Us Investigate (Gargaro, Murphy & Harris 2023) — cultivar subgroup",
    "notes": "Head type and market channel dominate. Living-head butterhead (Alberta AgriProfit$ high-return crop) is not the same product as iceberg kg/m²."
  },
  {
    "effect_size": null,
    "effect_unit": "",
    "ci_lower": null,
    "ci_upper": null,
    "conditions": "2023 Alberta greenhouse survey. Lettuce recorded the highest gross return per square metre among the crops reported (ahead of tree seedlings, bedding plants/ornamentals, cucumbers, peppers, and tomatoes). Total production cost for lettuce houses was also the highest ($194.39/m²). Fast cycle supports multiple turns per year.",
    "study_count": 1,
    "comparison_count": null,
    "source_url": "https://open.alberta.ca/dataset/fbb2b0b5-53b9-4dbd-92b7-f37ec8ed9369/resource/f4313ce0-1ea0-45e0-bc34-18306b1d2128/download/agi-economics-production-marketing-greenhouse-crops-2023.pdf",
    "potential_yield_effect": null,
    "geography": "Alberta",
    "intervention": "Observed lettuce enterprise",
    "comparator": "Other Alberta greenhouse crops",
    "dose": "",
    "dose_unit": "",
    "limitations": "Survey year 2023. Lettuce area in Alberta is small relative to cucumber.",
    "source_year": 2025,
    "doi": "",
    "baseline": "",
    "factor_id": "lettuce-agriprofits-gross-return",
    "crop_id": "lettuce",
    "factor": "Alberta AgriProfit$ 2023 lettuce gross return per m²",
    "factor_category": "Economics & Certification",
    "direction": "positive",
    "effect_type": "other",
    "evidence_type": "economic_benchmark",
    "evidence_strength": "High",
    "prairie_relevance": "high",
    "source_title": "Economics of Production and Marketing of Greenhouse Crops in Alberta 2023 (Laate)",
    "notes": "Highest receipts/m² and highest costs/m². DLI and cultivar choices should be evaluated on margin per m² per year, not per-cycle biomass alone."
  },
  {
    "effect_size": null,
    "effect_unit": "",
    "ci_lower": null,
    "ci_upper": null,
    "conditions": "Indoor/vertical-farm lettuce ‘Casey’ and ‘Dragoon’. Downward airflow 0.4–1.3 m/s × PPFD 200–500 µmol m⁻² s⁻¹. Airflow and light independent. Airflow >0.4 m/s reduced tipburn and increased % marketable plants without changing shoot biomass. High light raised biomass but worsened tipburn. 1.0 m/s gave 100% marketable ‘Casey’ even at 350 µmol. Classic target: downward air >0.3 m/s at the meristem (Goto & Takakura 1992; Shibata et al. 1995).",
    "study_count": 2,
    "comparison_count": null,
    "source_url": "https://journals.ashs.org/hortsci/view/journals/hortsci/60/12/article-p2354.xml",
    "potential_yield_effect": null,
    "geography": "Indoor vertical farm / CEA lettuce",
    "intervention": "Downward canopy airflow ≥0.4 m/s",
    "comparator": "Low airflow (≤0.4 m/s)",
    "dose": "",
    "dose_unit": "",
    "limitations": "Indoor farm, not a sunlit greenhouse. Biomass unchanged; marketable fraction is the yield metric.",
    "source_year": 2025,
    "doi": "",
    "baseline": "",
    "applicability": "near-direct",
    "evidence_tier": "B",
    "factor_id": "lettuce-downward-airflow-tipburn",
    "crop_id": "lettuce",
    "factor": "Downward airflow ≥0.4 m/s to cut tipburn and raise marketable fraction",
    "factor_category": "Climate",
    "direction": "positive",
    "effect_type": "yield_gain",
    "evidence_type": "greenhouse_trial",
    "evidence_strength": "High",
    "prairie_relevance": "high",
    "source_title": "Optimizing Downward Airflow to Prevent Lettuce Tipburn in Vertical Farms (HortScience 2025)",
    "notes": "Saleable yield, not fresh weight. Tipburn of a few inner leaves can zero a head. Alberta winter LED lettuce at high DLI will hit this constraint unless fans are specified."
  },
  {
    "effect_size": null,
    "effect_unit": "",
    "ci_lower": null,
    "ci_upper": null,
    "conditions": "Greenhouse hydroponic ‘Rex’. Control (no VAF, no biostimulant): tipburn rating 5.0 and 39% of leaves at 28 DAT. Biostimulant 0.5 mL/L cut tipburn 94–96% at 21 DAT and 71–75% at 28 DAT without VAFs, comparable to fans. Shoot mass transiently −16–32% at 14–21 DAT at the highest dose; by 28 DAT biomass matched the control.",
    "study_count": 1,
    "comparison_count": null,
    "source_url": "https://doi.org/10.3389/fpls.2025.1701667",
    "potential_yield_effect": null,
    "geography": "Summer greenhouse hydroponic lettuce",
    "intervention": "Calcium-mobilizing biostimulant 0.5 mL/L",
    "comparator": "No fans and no biostimulant",
    "dose": "",
    "dose_unit": "",
    "limitations": "One cultivar, one product. Not a yield-increase claim.",
    "source_year": 2025,
    "doi": "10.3389/fpls.2025.1701667",
    "baseline": "",
    "applicability": "direct",
    "evidence_tier": "B",
    "factor_id": "lettuce-tipburn-biostimulant-vs-fans",
    "crop_id": "lettuce",
    "factor": "Calcium-mobilizing biostimulant vs vertical airflow for tipburn (no final biomass penalty)",
    "factor_category": "Biostimulants",
    "direction": "positive",
    "effect_type": "other",
    "evidence_type": "greenhouse_trial",
    "evidence_strength": "Moderate",
    "prairie_relevance": "moderate",
    "source_title": "A calcium-mobilizing biostimulant provides tipburn control comparable to vertical airflow fans in greenhouse hydroponic lettuce ‘Rex’ (2025)",
    "notes": "Greenhouse-soilless biostimulant evidence (a stated research gap). Effect is marketable quality, not extra grams. Highest dose had a transient biomass dip."
  },
  {
    "effect_size": 75.0,
    "effect_unit": "g/head less at 1.4 vs 1.8 mS/cm (‘Green Butter’)",
    "ci_lower": null,
    "ci_upper": null,
    "conditions": "NFT lettuce. Max yield at ≥1.8 mS/cm for Green Butter (263 g) and Red Butter (202 g), ≥1.6 for Red Oakleaf (183 g). Green Butter was 75 g lighter at 1.4 than at 1.8 mS/cm; tipburn was lower at 1.4. pH 6.0–6.2 maximized yield. Foliar CaCl2 400–800 mg/L twice weekly cut tipburn with minor yield cost vs lowering EC.",
    "study_count": 1,
    "comparison_count": null,
    "source_url": "https://journals.ashs.org/hortsci/view/journals/hortsci/55/8/article-p1265.xml",
    "potential_yield_effect": null,
    "geography": "Greenhouse NFT lettuce",
    "intervention": "Solution EC 1.4 vs 1.8 mS/cm",
    "comparator": "Cultivar-specific EC optimum",
    "dose": "",
    "dose_unit": "",
    "limitations": "Three butter/oakleaf cultivars. 75 g is an absolute difference, ~28% of the 263 g high-EC head, not a universal EC elasticity.",
    "source_year": 2020,
    "doi": "",
    "baseline": "",
    "applicability": "direct",
    "evidence_tier": "B",
    "factor_id": "lettuce-nft-ec-yield-tipburn",
    "crop_id": "lettuce",
    "factor": "Nutrient-solution EC: yield vs tipburn trade-off",
    "factor_category": "Nutrients",
    "direction": "nonlinear",
    "effect_type": "dose_response",
    "evidence_type": "greenhouse_trial",
    "evidence_strength": "Moderate",
    "prairie_relevance": "high",
    "source_title": "Effects of Electrical Conductivity, pH, and Foliar Application of Calcium Chloride on Yield and Tipburn of Lactuca sativa Grown Using the Nutrient–Film Technique (2020)",
    "notes": "Nonlinear: raising EC raises head mass and tipburn together. Saleable yield may peak below maximum fresh weight."
  }
]