What the Soil Test Tells Us (Hilo, August 2022)
According to the University of Hawaiʻi–Hilo lab results, the soil (probably volcanic in origin, given your context) shows:
- pH: ~5.45 (slightly acidic)
- Organic Matter (Loss on Ignition): ~29% — quite high, which is excellent for soil biology (Shopify).
- Cations (mg/kg): Calcium ~55, Magnesium ~26, Sodium ~73, Potassium ~7.8
- Phosphorus (as PO₄–P): ~2.9
- Nitrate + Nitrite (as N): ~27
- Ammonium (as N): ~0.7
Interpreting this for your palms:
- pH is slightly low, but acceptable for coconut palms (preferably around 5.5–6.5).
- Organic matter is superb—your soil has excellent structure and microbial potential.
- Potassium (K) is low—coconuts are heavy K feeders.
- Phosphorus (P) is moderate—ok, but could be boosted.
- Nitrogen (N) (via nitrates) seems moderate as well.
- Micronutrient data isn’t included, so deficiencies (like boron, manganese, zinc, etc.) may be lurking.
2. What Coconut Palms Typically Need
Coconut palms require a balanced mix of macronutrients and micronutrients:
- Macronutrients:
- Nitrogen (N) – for leafy growth
- Phosphorus (P) – root development & flowering
- Potassium (K) – vital for fruiting, stress tolerance, disease resistance (Gardening Know How, YARAFERT, Better Homes & Gardens)
- Micronutrients: Manganese, Boron, Zinc, Copper, Iron, Molybdenum—fronds yellowing or poor fruiting often indicate these are low (Gardening Know How, Agritech Tamil Nadu).
General fertilization guidance:
- A 2-1-1 NPK ratio is common, with a mix of fast- and slow-release nitrogen at planting, then switching to regularly scheduled granular or foliar feedings (Gardening Know How).
- Foliar feeding is often suggested every 1–3 months when palms are young; after establishment, granular applications 3–4 times per year suffice (Gardening Know How, Better Homes & Gardens).
- In region-specific recommendations (e.g., India’s TNAU), per tree per year: ~1.3 kg urea, 2 kg superphosphate, 3.5 kg muriate of potash (K), 50 kg FYM or compost, plus micronutrients like borax, zinc, manganese, copper, ferrous sulfate—all incorporated annually (Agritech Tamil Nadu).
3. What You Could Add Beyond the Inoculant
The Hawaiian Bokashi Inoculant™ adds beneficial microbes—great for soil biology and nutrient cycling (HawaiianVolcanicOrganic).
However, for mature, underperforming coconut palms (~18 years old), I’d also recommend:
1. Balanced NPK Fertilizer
- Use a palm-specific 2-1-1 NPK fertilizer or equivalent, or create your own:
- Example: 20 lb N, 10 lb P₂O₅, 10 lb K₂O mix (adjust per label for slow/fast release).
- Apply 3–4 times per year, timed around active growth—in Hawaii, possibly spring, summer, fall, and perhaps early winter.
- Ensure potassium gets a boost—it seems low relative to other elements in the soil test.
2. Organic Matter & Compost
- Though soil OM is already high, adding well-rotted compost or FYM (50 kg per tree annually) helps maintain microbial activity and soil structure (Agritech Tamil Nadu).
3. Targeted Micronutrient Boost
- Since they can be hidden in volcanic soils, consider a soil or foliar mix including:
- Borax (~50–200 g/tree/year depending on need)
- Zinc sulphate, manganese sulphate, ferrous sulphate, copper sulphate at small rates (e.g., 225 g each per tree, per TNAU-style guidance) (Agritech Tamil Nadu).
- Adjust based on visual symptoms—e.g., pencil-point fronds, chlorosis—or get a leaf tissue test to refine.
4. Foliar Feeding (if needed)
- If deficiencies appear (e.g., yellowing younger fronds), foliar sprays with micronutrient mixes can act faster than soil-applied forms (Gardening Know How).
Sample Annual Maintenance Plan
|
Season / Frequency |
What to Apply |
|
Early Year (Spring) |
Compost or FYM (e.g., 50 kg/tree) + balanced granular NPK (2-1-1 formula) |
|
Quarterly (4×/yr) |
Granular NPK applications to supply N, P, and especially K |
|
Mid-season |
Foliar micronutrient spray if deficiencies appear |
|
Once per year |
Soil or foliar supplementation with micronutrients (B, Zn, Mn, Fe, Cu) |
|
Throughout |
Use Bokashi inoculant to boost microbial health and nutrient uptake |
Final Thoughts
- Your soil has strong organic matter, but potassium is low and may be limiting growth.
- The bokashi inoculant supports soil health but doesn’t replace balanced fertilization—especially for long-lived palms.
- Adding balanced NPK, organic compost, and micronutrient support should help reverse stagnation.
- Monitor the palms for leaf color, frond size, fruit set, and trunk vigor—adjust rates as needed.
- If possible, a leaf tissue analysis can pinpoint micronutrient deficiencies for precise correction.