Ammonium application in soil and substrate

A high pH inhibits the uptake of nutrients. With ammonium containing fertilizers the pH in the root environment can be decreased. Different cultures/cultivation techniques demand a different approach.
The working of Ammonium ions in the soil are converted to nitrate ions by so-called nitrificating bacteriae. During this process H+ ions are released, causing a lower pH. This acidification process develops less effective when the soil contains high quantities of calcium carbonate. In that case the acidifying effect of ammonium application is considerably less. When ammonium is found in the (soil) analysis from the root environment this means that either too much water has been applied or that the ammonium gift is too high or that you have low oxygen in the root environment. Ureum is an example of an acidifying fertilizer. Ureum consists of an amide of carbonic acid, which is converted by ureum bacteriae to ammonium and then by nitrificating bacteriae to nitrate. In high calcium containing soils ureum should be worked through the soil carefully, otherwise ammonia is formed and evaporates.

Time of application

Acidifying fertilizers are recommended in our feeding program based on bicarbonate (HCO3) concentration in the plain water. In many soil types ammonium is calculated in the feeding solution based on pH, bicarbonate and ammonium concentration in the soil sample. The bicarbonate concentration has the largest influence on ammonium dosage. Ammonium is recommended mostly above pH 6.9.

Substrate cultivation

When you use new rockwool substrate the ammonium quantity is limited. For rose no ammonium is recommended in the standard feeding solution in the period half September until half February.
For peat substrates 10-20% of the nitrogen is applied via ammonium. Above a certain target pH extra ammonium is recommended.
The application of ammonium in a feeding solution is not always desirable. In tomato a high ammonium concentration in the root environment can cause root corking.

Please contact us, HORTICENTAR – Greenhouse training center, when you have questions about it and for more expert consultancy about it.