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How To Use Mono-Potassium Phosphate (MKP) as Foliar Spray

Updated: Oct 21, 2020

The use and purpose of MKP was discussed in my previous article here. This time I will share on how I prepare the solution and how I measure the concentration of the foliar spray for my farm's durian trees foliar spray usage.


monopotassium phosphate  fertilizer
A brand of MKP fertilizer sold in the market

The use of MKP as a foliar spray must be measured to prevent overdose to the trees. The signs of overdose are burnt and drying leaves including shedding of leaves.


Due to this, the preparation of the MKP solution is crucial. Measurement of concentration requires an analytical instrument which is the EC (electro-conductivity) meter. This instrument could be purchase at agriculture supply stores, lab equipment shops and via online cheaply.


This instrument measures the solution's electrical conductivity in uS/cm (micro Siemens per cm) and ppm (parts per million) units.


EC meter
EC meter with calibration pin and user manual


MKP Solution Preparation


MKP is a salt, white in color and has a high dissolve rate in water. Applied as a soil spread fertilizer by some growers but I will discuss the application of MKP as a foliar spray.


Steps for making a solution as below:

  1. The volume of the solution and the final solution concentration ideally should be estimated by the grower.

  2. Measure the initial mixing water mineral concentration (rain water, pond water, tap water etc.) with the EC meter.

  3. Dilute a small quantity of the MKP powder in the mixing water.

  4. Measure the concentration of the solution using the EC meter.

  5. Add small amounts of MKP powder until the measurement reaches the target concentration for foliar spray use.


Spray Volume and Concentration


The spray volume will depend on the number and size of the trees. This volume figure is meant only for the grower's personal record for subsequent spray preparations.


As far as I know, there is no set standards for MKP foliar concentration (either for durian saplings or adult trees) but my practice is to use the hydroponics AB liquid fertilizer EC chart as reference:


Hydroponics AB liquid fertilizer concentrations

As we can see, recommended EC concentrations for leafy vegetables have low values as compared to the higher recommended EC values for shrub/woody stem vegetables such as tomato plant, green beans and eggplants.


Comparing these values to say example a 2 feet high durian sapling, we could make a simple judgement that for a sapling of this size the EC concentration range should be between 2.5 - 5.0.


As a safety buffer to prevent leaf burn to the saplings, I'm taking the value of 2.5 EC as the concentration target.



Existing Mineral Content Measurement


Due to the mixing water to be use is not distilled water (approx. 0 EC), when measured with an EC meter the mixing water (tap water, pond water, rain water etc.) will have some small readings due to the dissolved mineral content.


This value must be deducted from the MKP solution EC measurement afterwards.


Note:

  1. Toggle the measurement unit of uS/cm and not ppm

  2. In the case of my EC meter, the reading should be multiplied by 10.

  3. Read the upper figure for EC, the bottom figure is for water temperature

It can be seen here in the display the reading is 010 X 10 = 100 uS/cm



Dilute MKP Powder and Mix


For this demonstration, I had diluted 4 grams of MKP powder into 1 liter of water. The solution is then mixed well.



Measure the Concentration of MKP Solution


As before step, the reading is:

263 X 10 + 2,630 uS/cm


EC meter measuring MKP concentration
EC reading after MKP added and diluted

The actual MKP concentration of the solution is:

Concentration (after dilution) - Concentration (before dilution) = Final concentration


In other words 2,630 uS/cm - 100 uS/cm = 2,530 uS/cm


This value is measured in uS/cm while the concentration table that we refer to earlier is in EC units. To convert uS/cm to EC we shall divide the value with 1,000. We now have 2.53 EC as the target concentration.



Adding MKP Powder To Achieve Target Concentration


It can be seen that I had prepared a 1 liter foliar solution with a concentration of 2.53 EC which is approximately the same as my desired concentration, as such no additional MKP is required to be added and dissolved.


In the case of a 4.5 EC concentration is required, I shall then add MKP powder gradually while making measurements after each addition.


With this demonstration I can safely record that as a general rule (depending on the mixing water dissolved mineral concentration), that 4 grams of MKP diluted in 1 liter of water would have a concentration of 2.5 EC.


It must be understood that during the course of subsequent sprays, the grower shall observe and note the positive or negative affect that the MKP foliar has towards his/her durian trees.


This will give the grower some indication on whether to reduce or increase the MKP concentration for subsequent sprays.


It was quite interesting for me to write and share this step-by-step guide for preparing MKP as a foliar spray. I would appreciate some comments in the comment form below.


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