Moisture measurements in root balls: why increasingly important and how to do it right?

29 september 2020

A change in substrate recipes also means a change in the water balance in the root ball. Growers must adjust their watering strategy accordingly. To do this properly, insight into a number of parameters is important. Hans Verhagen, head of Research at RHP, was interviewed about this in the Dutch magazine Onder Glas number 8 (pages 44-45). Here is a brief overview of the how and why of moisture measurements. 

Why are moisture measurements becoming increasingly important?

  • Because the composition of substrates is changing more and more, and with that the water balance in root balls is different. 
  • Because even small changes in the recipe can have major consequences for the pore volume, the rate of water uptake, the water distribution and the water content in the substrate. 
  • Because growers have to adjust their watering strategy to the water balance in root balls. And that is only possible with insight in the air and water balance. That is why measuring is necessary. 
  • Because research and practice show that the water content and water distribution in root balls can deviate considerably from the expectations. 
  • Because watering too little or too much for a longer period of time can lead to problems such as production loss, deficiency symptoms and reduced resistance to diseases and pests. This is because plant roots can only develop properly in a substrate in which sufficient moisture and oxygen is present. This also ensures that the plant can properly uptake nutritional elements. 

How to do moisture measurements right?

  • By inserting moisture sensors horizontally into the root ball, at least at two different heights. This shows layers that are structurally too dry or too wet in the root ball. Sensors that are inserted vertically into the root ball only give information about the average water content over time. 
  • By measuring at several places in the culture and not just in a single pot. 
  • By making measuring a regular routine. By doing this structurally and not just once in a while. Then you get to know the relationship between growing medium, water balance and crop development much better and you can targeted optimize the irrigation. 
  • By ensuring that the moisture sensors are properly calibrated. 
  • By not forgetting that the water balance is also influenced by the way of potting. Read more about the Potting reference developed by RHP. 

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