pH

The ability of the plant to take up the nutrients it requires is affected by the pH of the nutrient solution. This means that it is very important to have the correct pH around the root sytem. The picture below shows the uptake of different elements at different pH levels.

The optimal pH for most plants is between 5.5 and 6.5 and this should be the target level.  The pH in slabs can change because of selective root uptake. When NH4 is transported into the roots, the pH will drop. When NO3 is transported into the roots, pH will rise. Also NH4 and NO3 can be used by micro organisms, that will also influence the pH in the substrate. The change of concentration of the fertilizers NH4 and NO3 can influence the pH in the substrate.

So it is important that the pH of the source water is corrected to the right pH at the irrigation rig. Take care:

• if the bicarbonate levels are very low (no buffer) in the source water it may be necessary to add bicarbonate to give some buffer;
• with low bicarbonate levels it may be necessary to dilute the acid used for pH correction to avoid a sudden decrease in pH to below 5.0;
• with amonium also with low bicarbonate levels which can cause a sudden decrease in the pH.

Always check the pH of the source water in the storage tank, at the irrigation rig and at the dripper. pH levels of below 5.0 will damage the roots. Remember the plant gets the water that is coming out of the dripper so that has to be right!