KNOWLEDGE · FOLIAR
MKP foliar spray: the 0.2% rule and what not to mix
Monopotassium phosphate (MKP, 0-52-34) is the most concentrated fully-soluble phosphorus-potassium source available. It works, and it is also the product most often applied at the wrong concentration. This guide covers rates, timing, mixing constraints and drone application.
What MKP does in the plant
Phosphorus drives cell division, so it determines how many cells a fruit can have. Potassium drives sugar transport and osmotic regulation, so it determines how large and how sweet those cells become. Applied at fruit set, MKP supports both; applied too late, it cannot add cells that were never formed.
Because MKP carries no nitrogen and no chloride, it can be used during ripening without pushing vegetative growth or adding salt load.
Concentration by crop and stage
| Crop / stage | Concentration | Interval |
|---|---|---|
| Fruit trees, fruit sizing | 0.2–0.3% | 7–10 days, 2–3 sprays |
| Vegetables, fruiting | 0.2% | 7 days, 2–3 sprays |
| Rice / wheat, grain filling | 0.2–0.3% | 1–2 sprays |
| Seedlings / nursery | 0.1% | Single application, test first |
| Drone application | Per spray plan | Use flying-grade MKP only |
0.2% means 200 g in 100 litres of water. In hot weather take the lower figure: evaporation concentrates the droplet before it dries, and leaf burn is a concentration problem, not a product problem.
Timing
Spray early morning or after 4 pm. Avoid spraying when the temperature is above 32 °C or when rain is expected within four hours. The most valuable single application for fruit crops is at fruit set, not at harvest — cell number is fixed early.
Tank-mix compatibility
MKP solution is mildly acidic (pH 4.3–4.7). Two combinations cause trouble:
- Calcium products — calcium phosphate precipitates, blocking nozzles and losing both nutrients
- Copper-based fungicides — can form insoluble complexes in hard water
Always run a jar test: mix a small quantity at the intended ratio, wait 30 minutes, and check for cloudiness or sediment before filling the tank.
Drone application
Agricultural drones spray 15–30 litres per hectare, far less than ground sprayers. Standard crystal MKP dissolves slowly and can leave undissolved particles that clog fine nozzles; flying-grade MKP is milled and formulated for rapid dissolution. In our own trial series, drone-applied MKP raised fruit count per plant by 53.3% against another brand of MKP, and shoot length by 22.6%.
Frequently asked
Can I mix MKP with urea?
Yes, they are compatible and a common combination for grain filling. Keep the total salt concentration below about 1% to avoid leaf burn.
What is the difference between crystal and膨化 (puffed) MKP?
Puffed MKP has lower bulk density and dissolves faster, which matters for spray preparation speed. Crystal is cheaper and suited to root application.
How many times can I spray MKP in one season?
Two to three applications at 7–10 day intervals are typical. More than that rarely pays back unless the crop shows a specific deficiency.