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Comprehensive research report on NPK (nitrogen, phosphorus, potassium) absorption (g/m²) by growth stage of lettuce
Overview
This report systematically summarizes the absorption amount (g/m²) of nitrogen (N), phosphorus (P), and potassium (K) in lettuce at each major growth stage (germination stage, seedling stage, growth stage/heading stage, bolting stage, flowering stage, and fruiting stage) based on Japanese and international scientific and agricultural data. If there is direct data on the amount of absorption by stage, we will introduce that value, and if there is insufficient data, we will clearly state the yield, number of growing days, and estimation method, and present it in a format that can be used in the field. If there are any assumptions (varieties, environmental conditions, cultivation methods, etc.), we will also explain their effects.
Lettuce growth stage classification and NPK absorption characteristics
The general growth stages of lettuce are classified as follows.
- Germination period (seed sprouting to twin leaves)
- Seedling stage (true leaf development to rooting expansion)
- Growing period/heading stage (vigorous elongation of leaves to head formation/before harvesting) )
- Bolting, flowering, and fruiting stage (Bulking to flowering/seed formation: Mainly for seed production)
In the case of conventional production in Japan and overseas (especially head lettuce), stages 1 to 3 are the most important because they are harvested before bolting, flowering, and fruiting. However, in seed production and special cultivation, absorption continues and increases to stage 4 [1][2][3][4][5].
Actual and estimated values of NPK absorption by stage
Actual Value: Korean Greenhouse Lettuce Test (Soil Cultivation/Drip Irrigation)
In an actual measurement study of greenhouse lettuce (plant type) in South Korea, the total nutrient uptake (70 days, 1,000m² plot) was measured as follows [1][3]:
- Nitrogen (N): 589.5g / 1,000m² → 0.5895g/m²/1 production
- Phosphoric acid (P₂O₅): 197.2g / 1,000m² → 0.1972g/m²
- Potassium (K₂O): 2,770.2g / 1,000m² → 2.7702g/m²
The absorption rate for each growth stage (divided by DAS = days after sowing) is as follows:
| Growth stage | N Absorption rate | P₂O₅ Absorption rate | K₂O Absorption rate |
|---|---|---|---|
| Germination/seedling stage (~40 days) | 26% | 24% | 20% |
| Initial expansion (40-50 days) | 17% | 3% | 31% |
| Rapid growth (50-60 days) | 20% | 12% | 12% |
| Before heading/harvesting (60-70 days) | 37% | 50% | 34% |
From this result, the absolute absorption amount per 1 m² (g/m²) is estimated as follows (rounded to the nearest whole number):
| Stage | N | P₂O₅ | K₂O |
|---|---|---|---|
| Germination/seedling stage | 0.15 | 0.05 | 0.55 |
| Initial expansion | 0.10 | 0.01 | 0.86 |
| Rapid growth | 0.12 | 0.02 | 0.33 |
| Before heading and harvesting | 0.22 | 0.10 | 0.94 |
(Total is approx. 0.59g N, 0.18g P₂O₅, 2.68g K₂O/m²/crop, which is within the range of actual measurements) "Japan's Fertilizer Standards and Demand (Whole Lettuce)">
The recommended amount of fertilizer in Japan's typical cultivation guidelines (fertilizer application science, agricultural guidelines, etc.) is
- N, P₂O₅, K₂O both:1.0~1.5g/m²/production
- Example: 10~15kg (1.0~1.5g/ m²)
This value is designed assuming that the actual amount of fertilizer absorbed by crops and the amount of fertilizer applied are approximately the same (in some cases, it is added in anticipation of some soil erosion and operational loss) [6][7].
By applying the actual measured proportions by stage (such as the Korean data above), it is easy to estimate the absorption based on Japanese standards. For example,
- If the total N absorption is 1.2 g/m², "before heading and harvesting" is approximately 0.44 g/m² (1.2 g × 37%)
Characteristics of international cases and absorption trends
The University of California (UC Davis) and international literature [2][4][5] also reported an S-shaped curve in which ``germination/seedlings → rapid increase → peak at head-heading stage → continued even at bolting'', and the period from head-heading stage to pre-harvest coincides with the maximum period of nitrogen absorption.
In the case of seed production (cultivated until the bolting and fruiting stages), it has been recorded that absorption tends to be maintained or increased even after seeding [5].
NPK absorption until bolting, flowering, and fruiting stage
General Japanese cultivation for heading and shipping ends before harvesting, so there is usually no need to maintain fertilizer effectiveness until bolting, flowering, and fruiting. However, for seed collection and special uses (saladana type, unheaded harvest, etc.), it is necessary to continue absorption even after the seeds have set. In overseas literature on seed production, it has been confirmed that N absorption further increases and K absorption also peaks during the head-heading to bolting period [5].
Estimation method when there is no direct data - Rationale
When there is no direct absorption measurement value, the following method is appropriate as an estimation method.
Based on the fertilizer application guideline and absorption estimation (e.g. 1.0 to 1.5g/m²), multiply the actual measured rate by stage
- Example: N 1.2g/m² × Absorption rate for each stage (see table above)
Estimated from growth days and dry matter weight trends
- Dry matter increase ratio up to the time of harvest is apportioned as increase in absorption amount, and Korean measured ratios and UC are used as necessary. Using Davis's growth curve・The head-heading stage is the most important.'' ``A small amount is sufficient during the germination and seedling stages.''
These multiple methods are internationally consistent, and unless the cultivation environment is extremely special, this estimation method is reliable enough in practice.
Variation factors and notes
- Cultivated varieties/methods: Absorption ratios and absolute values may differ slightly depending on suntu leaf lettuce, etc., and hydroponic types (NFT, culture medium).
- Environment/fertilization method: Efficiency and soil retention capacity differ depending on greenhouse/open field, drip irrigation/regular fertilization. General recommendations are valid in most situations.
- Harvest type: The total absorption amount and distribution are different for commercial shipment and for seed production. Most commercial cultivation in Japan involves "pre-heading harvest."
- Soil conditions/crop season: Separate correction is required in cases of extremely fertile land, excessive topdressing, early/late ripening, etc.
Summary table of NPK absorption trends by growth stage (made by g/m²/1, typical values)
| Stage | N | P₂O₅ | K₂O | Notes |
|---|---|---|---|---|
| Germination stage/seedling stage (~40 days) | 0.15 | 0.05 | 0.55 | Approximately 20-25% of total absorption |
| Initial expansion (40-50 days ) | 0.10 | 0.01 | 0.86 | |
| Growing season・Rapid growth (50-60 days) | 0.12 | 0.02 | 0.33 | |
| Before heading/harvest (60-70 days) | 0.22 | 0.10 | 0.94 | Maximum absorption period is from just before bulbing to seedling period Assuming 1.2g/m² of P₂O₅, K₂O each, representative value proportionally divided from Korean actual measurement ratioOverview
Sources [1] Characteristics of Growth-Stage-Based Nutrient Uptake of Lettuce Grown by Fertigation in Greenhouse (Korean Journal of Soil Science and Fertilizer): https://www.kjssf.org/articles/article/vJjg/ |