Introduction: Use of DAP in Potato Cultivation
Use of DAP in potato cultivation is a game-changer for achieving higher yields and healthier crops. The right DAP application can mean the difference between average and exceptional results. In Pakistan’s potato-growing regions like Lahore, where phosphorus deficiency is common due to alkaline soils, Di-Ammonium Phosphate (DAP) serves as a crucial fertilizer input.
Containing 46% phosphorus and 18% ammoniacal nitrogen, DAP boosts early plant development, root expansion, and tuber initiation. This guide explains the use of DAP in potatoes—covering its mode of action, best application timing, local fertilizer schedules, and ways to prevent phosphorus fixation.
For broader context, explore our comparison of agriculture practices in Pakistan vs USA (internal link).
What is DAP Fertilizer and Why the Use of DAP is Critical for Potatoes
- Chemical Name: Di-Ammonium Phosphate
- Formula: (NH₄)₂HPO₄
- Composition:
- Phosphorus (P₂O₅): 46%
- Nitrogen (N): 18% (Ammoniacal form)
Potatoes require phosphorus in large amounts during the early growth phase for root development and tuber formation. The use of DAP provides a soluble, readily available source of phosphorus, critical for early-stage success in the field.
🔗 External Resource: Learn more from the International Cotton Advisory Committee on DAP
Use of DAP: Mode of Action in Potato Fields
| Component | Action in Soil | Role in Potato |
|---|---|---|
| Ammonium (NH₄⁺) | Dissolves and is absorbed or nitrified | Supports vegetative growth, chlorophyll |
| Phosphate (HPO₄²⁻) | Absorbed or bound by calcium in alkaline soils | Critical for energy (ATP), root expansion, tuber initiation |
In Pakistani alkaline soils, phosphorus begins to fix within 3–5 days after application. Without corrective measures, up to 80% can become unavailable within three weeks. This makes timing and method of DAP application essential.
For more on fertilizer efficiency, refer to Soil Fertility & Fertilizer Management by FAO.
🗓️ When and How to Use DAP in Potato Crop for Best Results
Here’s a detailed breakdown of when to apply DAP, why it’s needed at that stage, and how to optimize its uptake.
1. At Planting (Basal Application)
| Timing | DAP Rate | Why DAP is Needed Here | Method |
| Day 0–1 | 1.5 bags (75 kg/acre) | Potato seedlings need phosphorus during the first 2–3 weeks to develop roots and initiate tubers | Band placement 5–10 cm below tubers |
Scientific Note: The use of DAP at planting is effective before soil fixation peaks. Nitrogen supports foliage development for better photosynthesis.
2. 15–20 Days After Planting (First Irrigation)
| DAP Status | Why Not Reapplied | What to Add Instead | Why This Helps |
| Fixed or Bound | Phosphorus is no longer available | Urea + PSB + Micronutrients | Urea boosts N; PSB unlocks bound P; micronutrients aid enzyme functions |
Why the use of DAP isn’t repeated: Phosphorus has low mobility in soil, so post-planting application is inefficient. Use PSB (Phosphate Solubilizing Bacteria) to reactivate bound phosphorus.
Read more on Phosphate Solubilizing Microbes and their role in nutrient uptake.
3. 35–40 Days After Planting (Second Irrigation)
| DAP Role | Why It’s Still Important | What to Apply |
| Indirect via PSB | Tuber bulking increases phosphorus demand. Reactivated DAP helps. | Urea, Boron (1–2 kg), KNO₃ foliar (optional) |
✅ Boron improves tuber quality and prevents disorders like internal necrosis. Potassium nitrate strengthens plants under moisture stress.
4. 60–70 Days After Planting (Tuber Bulking Peak)
| Why DAP Isn’t Reapplied | What to Focus On Instead |
| Fixed phosphorus can’t be absorbed | SOP (Sulphate of Potash) + Foliar micronutrients |
Why DAP Becomes Unavailable — and How to Fix It
❌ Causes of Fixation:
- High pH (alkaline soils)
- High calcium (common in Punjab)
- Low organic matter
✅ How to Break Soil-Bound DAP:
| Technique | Effect |
| Add FYM/Compost | Increases organic acids and microbial activity |
| Apply PSB | Reactivates fixed phosphate |
| Elemental Sulfur | Lowers pH and dissolves calcium phosphate compounds |
| Avoid DAP + Urea | Prevents nitrogen loss through ammonia volatilization |
Localized DAP Schedule for Potato Crop (Lahore, Punjab)
Target Yield: 10–12 tons/acre
✅ Basal (Planting Stage)
| Fertilizer | Rate | Purpose |
| DAP | 1.5 bags | Early root/tuber development |
| SOP | 1 bag | Improves tuber size, quality |
| Zinc Sulfate | 10 kg | Boosts enzyme activity and root growth |
| FYM | 2–3 tons | Reduces fixation and improves uptake |
✅ First Irrigation
- Urea: ½ bag
- PSB: As per label
- B + Zn Spray: Foliar
✅ Second Irrigation
- Urea: ½ to 1 bag
- Borax: 1–2 kg
- KNO₃: 10–15 kg foliar (optional)
✅ Tuber Bulking
- SOP: 25 kg top-dressed
- Micronutrients: As needed
Fertilizer Budget Per Acre (Approximate)
| Fertilizer | Quantity | Cost (PKR) |
| DAP | 1.5 bags | ~11,000 |
| Urea | 1.5 bags | ~6,000 |
| SOP | 1.5 bags | ~8,500 |
| FYM | 3 tons | ~3,000 |
| Zn, B, PSB | Mixed | ~3,000 |
| Total | — | ~33,500 PKR |
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