Spinach — NPK Absorption (g/m²) by Growth Stage

Overview

This report quantifies nitrogen (N), phosphorus (P), and potassium (K) uptake (g/m²) by spinach at germination, vegetative growth, and bolting/flowering, from major Japanese and international agronomic literature. Direct stage-specific data are rare; estimates use dry-matter growth, duration, and tissue concentration where needed.

Growth Stages and Nutrient Uptake

1. Stage Overview

• Germination (0–2 weeks): Cotyledon expansion; very slow growth and uptake.
• Vegetative (~3–5 weeks): True leaf increase and rapid dry-matter gain; peak NPK demand.
• Bolting / flowering: Most leaf crops harvested before bolting; uptake slows or is irrelevant for fresh market spinach.

2. General NPK Trends

• Minimal uptake in germination; sharp increase in late vegetative growth to pre-harvest peak.
• Stage amounts can be estimated from dry-matter curves and tissue NPK concentration.
• Japanese literature notes sharp N uptake increase after ~23 days from sowing[1].

Stage-wise NPK Uptake (g/m²) — Measured and Estimated

1. Germination (0–2 weeks)

• N: 0.78 g/m²; P: 0.07 g/m²; K: 0.81 g/m²

Reference: Heinrich et al. (2013)[2] report 7.0 lbs/acre N in the first 2 weeks (= ~0.785 g/m²); P and K converted similarly.

2. Vegetative (2–4 weeks: rapid growth)

• N: 6.75 g/m² (= 0.48 g/m²/day × 14 days); P: 0.94 g/m²; K: 12.25 g/m²

Reference: Daily uptake rates integrated over 14 days[2][3].

3. Bolting / Flowering

• Little quantitative data for fresh-market crops; harvest ends at vegetative peak—≈0 additional uptake in practice.

Totals

Stage	N (g/m²)	P (g/m²)	K (g/m²)
Germination	0.78	0.07	0.81
Vegetative	6.75	0.94	12.25
Bolting / flowering	≈0	≈0	≈0
Total	7.54	1.01	13.06

Most NPK uptake occurs from germination through vegetative growth.

Calculation Basis

• 1 acre = 4,046.86 m²; 1 lb = 453.592 g
• Example: 7.0 lbs/acre N = 7.0 × 453.592 / 4,046.86 ≈ 0.785 g/m²
• Vegetative period: dry-matter increment × tissue NPK concentration[2][3][4]

Japanese and International Agreement

• Japanese source[1]: uptake rate rises sharply after day 23; overseas sources[2][3]: slow early, main uptake in late vegetative period.
• Bolting-stage uptake is rarely relevant for fresh spinach.
• Major fertilization models align with this division[2][3][4][5].

Conclusion

• Spinach NPK uptake surges in the second half of the crop cycle (weeks 3–harvest); germination uptake is small.
• Stage amounts are derivable from dry-matter, duration, and concentration data.
• Practical guides: ~0.8 g/m² N/K in early weeks; ~6–13 g/m² (N/K) and ~1 g/m² P in main vegetative period.
• Bolting-stage uptake is negligible for fresh-market spinach.

Sources

[1] Effect of Drip Fertigation System on Nitrate Control in Spinach: https://www.jstage.jst.go.jp/article/dojo/77/1/77_KJ00004597967/_article/-char/en
[2] Nutrient and Water Use of Fresh Market Spinach in, ASHS Journals, Heinrich et al. 2013: https://journals.ashs.org/view/journals/horttech/23/3/article-p325.xml
[3] UCANR “Nutrient Uptake by Spinach” PDF: https://ucanr.edu/?legacy-file=138251.pdf&legacy-file-path=sites/uccemontereycounty/files/
[4] Nitrogen Use Efficiency in Spinach (Spinacia oleracea L.): https://edepot.wur.nl/288018
[5] Nitrogen fertilization strategies to reduce the risk of nitrate leaching in baby leaf spinach production: https://opus.hs-osnabrueck.de/files/4978/Nitrogen_fertilization_strategies.pdf
[6] Growth and shoot:root partitioning of spinach plants as affected by nitrogen supply: https://www.researchgate.net/publication/230489800_Growth_and_shootroot_partitioning_of_spinach_plants_as_affected_by_nitrogen_supply
[7] Soil–Plant Nutrient Relationship at Different Growth Stages of Spinach as Affected by Phosphorus and Manure Applications: https://www.researchgate.net/publication/232883375_Soil-Plant_Nutrient_Relationship_at_Different_Growth_Stages_of_Spinach_as_Affected_by_Phosphorus_and_Manure_Applications

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This report summarizes current major agronomic data for fertilization and crop diagnosis.