How Can We Help?

< All Topics
Print

Fertilizer Solubility – Dissolve a Fertilizer

When applying fertilizers through the irrigation water (fertigation), it is essential to be familiar with some important facts regarding fertilizers solubility.

Solubility of a fertilizer – The solubility of a fertilizer is defined as the maximal amount of the fertilizer that can be completely dissolved in a given amount of distilled water at a given temperature.

Manufacturers may provide you with solubility data of their fertilizers upon request. Here is an example of solubility data of various fertilizers (expressed in  g/liter):

 Solubility g/l
Fertilizer / Temperature (C˚)51020253040
Potassium nitrate133170209316370458
Ammonium nitrate118315101920...
Ammonium sulfate710730750...
Calcium nitrate 102011301290...
Magnesium Nitrate680690710720..
MAP (Mono Ammonium Phosphate)250295374410464567
MKP (Mono Potassium Phosphate)110180230250300340
Potassium chloride229238255264275.
Potassium sulfate8090111120..
Urea78085010601200..

Different manufacturers may provide slightly different solubility data for the same fertilizer. This is because they use different additives in their products. There are also some fertilizers that may contain insoluble residues.

DISSOLVING A FERTILIZER

When you dissolve a fertilizer, you should not exceed its solubility. Otherwise, a precipitate may form and might clog the irrigation system. Moreover, the nutrients you intend to provide through the solution may not be fully available.

For example, according to the data in the table above, the solubility of Potassium Nitrate in 20oC is 209 g/l and the fertilizer contains 38% Potassium. If you attempt to dissolve 300 g/l in the fertilizer stock tank, you will not get 114 g/l of Potassium (38% of 300g), but only 80g. The remaining 34g will precipitate and will not be available.

MIXING FERTILIZERS

When mixing fertilizers that contain a common element (for example potassium nitrate together with potassium sulphate) the solubility of the fertilizers is decreased. In such case, we cannot refer to the fertilizer solubility data alone. The same happens when the water used for dissolution is highly rich with minerals, e.g. calciummagnesium or sulphate.

In such cases, additional chemical reactions come into play, and calculations become more complex. Usually, these are not calculated in the field and instead, trial-and-error practices are common.

MIXING FERTILIZERS – FERTILIZER COMPATIBILITY

Some fertilizers should not be mixed together in one stock tank because an insoluble salt might form very quickly. An example for such incompatibility is mixing fertilizers that contain calcium with those that contain phosphate or sulphate.

Use this fertilizers compatibility chart:

Fertilizer compatibility in fertigation

THE JAR TEST

We’ve established that when mixing fertilizers, one must be familiar with the solubility data of the fertilizers used, as well as with the chemical reactions that may take place. In order to avoid unwanted precipitates, a common recommendation is to perform a “jar test”. In this test, the fertilizers are initially mixed in a jar containing the same water used for irrigation.

Complete dissolution Formation of a precipitate

The fertilizers should be mixed exactly in the same concentration as intended to be used in the stock tanks. If a precipitate forms or if the solution has a “milky” appearance, the test should be repeated with lower concentrations of the fertilizers. 

  • Recommends the ideal fertilizer mixture/ blends
  • Saves up to 50% on fertilizer costs
  • Comprehensive data on hundreds of crop varieties
  • Interprets test results for any extraction method
Previous Chelated Fertilizers and Their Use
Next Fertilizing with Organic Matter
Table of Contents

Let's save the future together

Our goal is to pass on experience of eco-responsible farming
to new generations of agronomists to fight climate change together.

Copyright © 2021 Smart Fertilizer. All rights reserved