Nutrients in Kiwifruit and Kiwi Leaves
Introduction
Measuring ions in leaf and fruit juice with devices such as the HORIBA LAQUAtwin is extremely important for kiwi production. Juice measurements provide a snapshot of the nutrients actually moving within the vine, not just what is present in the soil. Soil tests alone are not sufficient, as nutrient availability in kiwis changes rapidly with spring growth, flowering, fruit set, canopy development, irrigation, and environmental stress.
The LAQUAtwin meters can measure K⁺, NO₃⁻, Ca²⁺, Na⁺, pH, and EC in fruits, leaves, soil, and water.
Why ion, pH, and EC meters are essential for kiwi farms
Why ion measurements matter
Modern kiwi production is no longer limited by fertilizer availability, but by nutrient balance, timing, and plant uptake efficiency. Disorders such as small fruit, uneven sizing, soft fruit, poor storage life, low dry matter content, internal breakdown, and reduced shelf life almost always result from nutrient imbalances during the growing season – not only at harvest. Therefore, real-time measurement tools – ion, pH, and EC meters – have become essential instruments for professional kiwi orchards.
Ion-specific measurements (K⁺, Ca²⁺, NO₃⁻, Na⁺) provide direct insight into what the vine is actually taking up and transporting at that moment. Unlike soil tests or traditional leaf tissue analysis, juice ion measurements reflect the current physiological condition and allow growers to detect problems early – often weeks before visible symptoms or irreversible fruit damage occur.
Key advantages include:
- Early identification of K-Ca imbalances that affect fruit firmness and storage
- Improved control of nitrogen-driven vegetative growth versus fruit development
- The ability to proactively adjust fertigation and foliar feeding programs
- Reduction of waste from unnecessary fertilizer applications
Why pH and EC are equally important
While ion meters show which nutrients are present, pH and EC explain why uptake succeeds or fails. pH determines nutrient availability and ion competition at root and leaf level. Even optimal Ca or K values are ineffective if pH conditions restrict absorption.
EC (electrical conductivity) provides a quick indicator of total salt concentration and osmotic stress. Elevated EC reduces water uptake, suppresses calcium movement, and often precedes sodium or chloride toxicity. Together, pH and EC measurements allow:
- Early detection of salt stress
- Diagnosis of irrigation and fertigation problems
- Correct interpretation of ion values and avoidance of misguided decisions
Juice preparation from kiwifruit or kiwi leaves
Sampling
- Select leaves or fruit
For leaves: Choose healthy, fully mature leaves from similar positions.
For fruit: Peel, chop, crush, or puree. Filter solids to collect clear juice. - Extract juice
Leaves: Use a petiole sap press (such as a garlic press) or a small hand press to squeeze out juice.
Kiwifruit: Crush or cut the kiwi and collect juice; filter solids so the sensor only comes into contact with clear liquid.
If needed, dilute samples with deionized or distilled water so the ion concentration falls within the calibrated measurement range.
Step-by-step protocol: Kiwi leaf sap (petiole sap) – Recommended method
1️⃣ Sampling
When: Morning (8–11 a.m.), avoid drought or heat stress.
Which leaves:
- Fully mature leaves from the middle vine position
- Avoid diseased or shaded leaves
Quantity: 20–30 leaves per block or variety.
Remove the petioles (leaf stems). The leaf blades dilute the sap and increase variability.
2️⃣ Juice extraction
Equipment:
- Garlic press or hand juice press
- Clean plastic cup
- Coffee filter or syringe filter (optional)
Procedure:
- Chop petioles into 5–10 mm pieces
- Press firmly to extract juice
- Collect ≥0.5 ml total juice
Typical yield: 20 petioles → approx. 0.4–0.9 ml juice.
3️⃣ Dilution (IMPORTANT for kiwis)
Kiwi juice is usually too concentrated for Ca and K meters.
Standard dilution (recommended starting point):
| Meter | Dilution |
|---|---|
| NO₃⁻ | 1:5 |
| K⁺ | 1:10 |
| Ca²⁺ | 1:10 |
| Na⁺ | 1:5 |
How to dilute (example 1:10): Mix 0.10 ml juice with 0.90 ml distilled/deionized water. Mix gently. Use disposable pipettes or syringes for accuracy.
Step-by-step protocol: Kiwifruit juice
- Sampling: 3–5 representative fruits, avoid damaged or overripe fruit.
- Juice extraction:
- Peel and chop
- Crush or puree
- Filter solids
- Collect clear juice
- Dilution: K, Ca: usually 1:5 or 1:10; NO₃⁻, Na⁺: often no dilution required.
Measurement
The device must be calibrated before measurement:
- Switch on the meter
- Rinse the sensor with demineralized or tap water and dry carefully with tissue
- Place 150 ppm solution on the sensor and press the CAL button
- Rinse and dry the sensor
- Place 2000 ppm solution on the sensor and press the CAL button
- Rinse and dry the sensor
- Place the extracted juice or sap on the sensor
- Wait for stabilization (takes a few seconds)
Expected values
These are typical working ranges, not absolute sufficiency standards. Kiwi juice varies greatly with variety (green vs. gold), crop load, irrigation, weather, and growth stage.
Kiwi leaf petiole sap (ppm, mg/L)
| Status | NO₃⁻ | K⁺ | Ca²⁺ | Na⁺ |
|---|---|---|---|---|
| Low | <300 | <1600 | <200 | -- |
| Adequate | 300–700 | 1600–3200 | 200–500 | <50 |
| High | 700–1200 | 3200–4800 | 500–800 | 50–150 |
| Excessive | >1200 | >4800 | >800 | >150 |
Kiwis require moderate nitrogen – excess N drives leaf growth at the expense of fruit quality. High K suppresses Ca uptake → soft fruit and poor storage. Sodium should be very low.
Kiwifruit juice (ppm, mg/L)
| Parameter | Range | Note |
|---|---|---|
| NO₃⁻ | <30 | High nitrate undesirable |
| K⁺ | 800–1200 | Excess → soft fruit |
| Ca²⁺ | >30 | Low Ca → poor firmness |
| Na⁺ | <20 | Indicates salt stress |
Stage-specific sap ranges
Leaf petiole sap (ppm, dilution-corrected) – Standard Green & Gold Kiwis
| Stage | NO₃⁻ | K⁺ | Ca²⁺ | Na⁺ |
|---|---|---|---|---|
| Budbreak – Early growth | 500–900 | 2600–4200 | 300–600 | <50 |
| Flowering – Fruit set | 400–700 | 2300–3600 | 350–650 | <50 |
| Early fruit growth | 350–600 | 2000–3200 | 400–700 | <50 |
| Mid season | 300–550 | 1800–3000 | 450–750 | <50 |
| Pre-harvest | <300 | 1500–2400 | 500–850 | <50 |
Kiwifruit juice targets (at harvest)
| NO₃⁻ | K⁺ | Ca²⁺ | Na⁺ | |
|---|---|---|---|---|
| Desired range | <30 | 800–1100 | >40 | <20 |
K:Ca ratio: < 20:1
K:Ca ratio (leaf sap)
The K:Ca ratio in kiwi leaf sap is important because it strongly affects fruit quality, storage life, and the risk of physiological disorders (especially bitter pit, soft fruit).
| Stage | Target |
|---|---|
| Early season | < 8:1 |
| Mid season | < 6:1 |
| Pre-harvest | < 4:1 |
Tips for kiwis & leaves
- Leaves (petiole sap): Best for rapid assessment of vine nutrient status during the season, especially nitrate and potassium.
- Consistency: Always sample at the same time of day and under similar conditions to reduce variability. Morning (8–11 a.m.) under non-stress conditions is most repeatable.
- Dilution: If the measurement range is exceeded, dilute and apply a correction factor (e.g. measured value × dilution ratio).
pH and EC
pH affects nutrient availability. Typical ranges: sap 5.5–6.5; irrigation water 6.0–7.0.
EC measures total salts. Target: leaf sap EC 1–3 mS/cm; irrigation water <0.75 mS/cm.
Advantages of LAQUAtwin devices for kiwi orchards
The HORIBA LAQUAtwin devices are ideal for orchard operations because they combine laboratory ion-selective technology with field practicality. Advantages: direct measurement of plant sap and fruit juice without complex preparation, minimal sample volumes, fast results for same-day decisions, and precise ion tracking.
In modern kiwi production systems, ion, pH, and EC meters are essential management tools for better balance, fruit quality, storage life, and cost savings.
