Current status and estimation method of NPK (nitrogen, phosphorus, potassium) absorption (g/m²) at each growth stage of cucumber (germination, seedling, flowering, fruiting)

Overview

In order to clarify the absorption amount (g/m²) of nitrogen (N), phosphorus (P), and potassium (K) at each growth stage (germination, seedling, flowering, and fruiting) of cucumber (Cucumis sativus L.), we will summarize the research results from the latest Japanese primary academic materials and agricultural instruction manuals. Currently, there is no direct absorption data for each stage, and the cumulative absorption amount over the entire growth period is mainly published. Therefore, we will focus on estimation methods and academically accepted models, and explain in detail how the absorption amount by stage is estimated in cucumber cultivation sites and research.

1. Presence and trends of direct data on the amount of NPK absorption in cucumbers

1.1 Current status of stage-specific absorption (g/m²) data

• Neither in Japan's major agricultural experimental stations, crop cultivation guidebooks [1][2][3], journal articles, or agricultural extension materials, NPK absorption (g/m²) data for clear growth categories such as "germination stage," "seedling stage," "flowering stage," and "fruiting stage" are not published.
• In Japan, the amount of NPK absorbed by cucumbers is expressed as a total value over the "entire growth period", and in most cases it is expressed in units such as "kg per 10a" or "g/m²" [1][2][3].
• Regarding the specific absorption pattern, it has been shown that the amount of absorption is very small during the "germination to seedling stage" and that the amount of absorption increases rapidly toward the flowering and fruiting stages [1][2][3].

1.2 Reference value of absorption amount during the entire growth period

• Estimated NPK absorption amount during the entire growth period (one crop) of cucumber (Japan, average for open fields and facilities):
  • Nitrogen (N): Approx. 20-33 kg/10a (2.0-3.3 g/m²)
  • Phosphoric acid (P2O5): Approx. 8-12 kg/10a (0.8 to 1.2 g/m²)
  • Potassium (K2O): Approximately 20 to 47 kg/10a (2.0 to 4.7 g/m²)
• The above absorption amount is repeatedly cited in "Soil Preparation and Fertilization Management" (Japan Soil Association) and in each prefecture's agricultural technical guidance and fertilizer management standards [1][2][3].

2. Approach for estimating removal amount by stage

2.1 Estimation based on growth curve/biomass ratio

• Nutrient absorption in cucumbers progresses almost in parallel with increases in the dry weight of the plant and the number of leaves. An academically accepted method is to divide the absorption amount over the entire period based on the dry weight and biomass increase rate for each growth stage [1][4][5].
• Example: A study by the Kochi Prefectural Agricultural Technology Center showed a high correlation between the dry weight increase curve and the NPK absorption curve, which was used as the basis for estimating the allocation to each stage [1].

2.2 Estimation formula for nitrogen absorption due to increase in number of leaves

• The Iwate Prefectural Agricultural Research Center and others have proposed a formula for estimating nitrogen absorption based on the value of increase in number of leaves, and empirical studies have shown high accuracy [4][5].
  • Formula example: "N absorption amount (g/m²/14 days) = increase in number of leaves (number of leaves/m²/14 days) x 0.0441 + 2.189"
• This method is effective for precision cultivation management and top dressing plans after the "seedling stage".

2.3 Time allocation method for the growing season

• If a direct growth index cannot be obtained, there is a method of allocating the amount of NPK absorbed over the entire period based on the number of days elapsed in each growth period or the ratio of general growth stages, and allocating it to each period. As a guide, it is often distributed at a ratio of approximately 5 to 15% during the germination/seedling stage, approximately 20 to 30% during the flowering stage, and approximately 55 to 70% during the fruiting stage.[1][3]

2.4 Estimation based on harvest/fruit set amount

• In reproductive crops like cucumbers, the most NPK is absorbed during fruit set, enlargement, and harvest, so it is also practical to estimate the amount absorbed based on the yield curve or number of fruits [1][2][3].

3. Reference: Absorption amount estimation model by stage (hypothetical example)

3.1 Configuration

If the total growth period N absorption is 3.0 g/m², P is 1.0 g/m², and K is 4.0 Example of distribution by stage based on estimated ratio:

Stage	Ratio	N (g/m²)	P (g/m²)	K (g/m²)
Germination period	5%	0.15	0.05	0.20
Seedling stage	10%	0.30	0.10	0.40
Flowering period	25%	0.75	0.25	1.00
Fruiting stage	60%	1.80	0.60	2.40
Total	100%	3.0	1.0	4.0

• The above is just an example of an allocation model [1][3] that is recommended in academic literature, etc., and in reality there are large variations depending on plant density, growing environment, tailoring/pinning method, cultivation period, and yield.
• P (phosphoric acid) has a low absorption efficiency, and tends to be absorbed in small amounts over almost the entire growth period, and is not concentrated in a particular stage [3].

4. Practical operation at Japanese agricultural guidance sites

• In agricultural guidance and extension sites in Japan, when seeking ``precise estimates of absorption by stage,'' it is recommended to use divisions and estimation formulas (especially nitrogen) based on biomass, number of leaves, yield, and number of days elapsed as described above, and provide feedback to actual leaf color diagnosis, soil testing, and fertilization plans as necessary.[1][3][4][5]
• Especially with regard to nitrogen, segmented fertilization based on real-time growth diagnosis such as leaf count index has been put into practical use in order to avoid folic acid deficiency and excessive risks [4][5].

5. Notes and future notes

• Estimated NPK absorption values for each stage vary greatly depending on the variety, climate, cultivation method (hydroponics/soil cultivation/outdoor/facility), and planting density.
• Since phosphoric acid is easily fixed in the soil and its absorption efficiency is low, it is difficult to accurately evaluate the absorption amount [3].
• As the latest field response method, it is essential to use it in combination with actual growth diagnosis and soil/leaf analysis.

Overview

Although direct primary data regarding the amount of NPK absorption (g/m²) in cucumbers during the germination, seedling, flowering, and fruiting stages is not published in Japan, allocation estimation based on growth volume, number of leaves, number of days, yield, etc. is widely adopted in academic and practical fields, and highly accurate estimation formulas, especially for nitrogen, have also been put into practical use. When performing fertilization and scientific evaluation, it is recommended to combine absorption data for the entire growth period with these segmentation models and make appropriate adjustments according to the actual field and cultivation conditions.

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Sources

[1] Growth and nutrient absorption of house cucumber under high fertilization conditions. Bulletin of the Kochi Prefectural Institute of Agriculture: https://meruka2.sakura.ne.jp/aid/data/Agriculture and Science March 1970/March 1970 issue_Ikuo Uesugi_Feed concentration in greenhouse soil, growth yield and nutrient absorption of cucumber.pdf
[2] "Fertilizer Application" BSI Biological Science Institute Cucumber: http://bsikagaku.jp/f-fertilization/cucumber.pdf
[3] Soil preparation and fertilization management tailored to the cultivation characteristics of vegetables. Japan Soil Association Booklet: https://www.japan-soil.net/BOOKLET/H23/H23_A4.pdf
[4] Utilization of nitrogen absorption estimation formula based on leaf number in simultaneous irrigation and fertilization cultivation of semi-forced cucumber. Japanese Journal of Farm Work Research: https://www.jstage.jst.go.jp/article/jsfwr1966/42/1/42_1_4/_pdf
[5] FY2017 Iwate Prefectural Agricultural Research Center Experimental Research Results: https://www.pref.iwate.jp/agri/_res/projects/project_agri/_page_/002/004/221/h29shidou_24.pdf