CF in tomato substrate
Over the past three seasons I have implemented a strategy using high conductivity factor (CF) levels in the stone wool substrate I use.
Four years ago I became very interested in using high CF levels, with sufficient water content (WC), in the substrate to grow a balanced plant with quality produce. I have been growing a cocktail tomato variety that weighs 40–55 grams per fruit and is truss pruned to eight. I would not grow a large loose tomato with the same aggressive approach as I would a cherry or cocktail tomato type. Neither would I do this if I was growing in any other media except stone wool.
It is very easy to monitor the CF in the substrate using a meter which measures conductivity, water content and temperature. I have one row that collects the run-off from over 100 plants and gives me real time information of the CF and PH (acid/alkaline) values in the drain water. I found that environments which have large variation in temperature and irrigation accuracy will restrict how aggressive you can be using higher CF targets. This is why it is massively important to have good, clean, accurate irrigation with low temperature variations in your greenhouse to maximise production from any type of crop.
Control the plants by using a higher CF at the beginning of the crop, which is the most critical time for any plant. Dry back the substrate and create a high CF to control the balance of the plant.
Lower the substrate CF and lift the WC.
Lower the substrate CF and increase the WC. (For me this phase occurs in spring time.)
I have used frequency and start and stop times to manipulate the CF and WC values of the plants, which in turn has enabled me to produce balanced crops. I have a calculated shot size on the amount of substrate volume each dripper supplies. Log on to my website www.grower2grower.co.nz for graphs containing achieved levels of CF and WC in the slabs and an explanation of dripper volumes.
Years ago I was advised that giving large shot sizes and fewer shots per day would encourage “generative action”. This technique can work but it is stressful for the plants (root stress leading to all sorts of other related problems) and in my opinion is neither necessary nor advisable to achieve a balanced high-producing plant Using large shots will dramatically change the CF value (delta electrical conductivity) in the root zone under your dripper (generally first shots in the morning) resulting in rapid uptake which could cause all sorts of quality issues. The volume per irrigation cycle in substrates can determine the structure of the root cone under your dripper. Some substrates have a dense layer at the top. In my opinion this substrate has limitations as it is necessary to push high electrical conductivity (EC) out of the dense layer with large shot sizes. This means you are obliged to use (and limited to using) the larger shot sizes advised by the salesman! Growers have different opinions on this and that is fine, but I have never seen scientific proof that this is what plants require, and in my own growing experience this method, which I have used in the past, caused me far too many complications!
“Transpiration before Irrigation” (codswallop) is another discussion associated with my article but I have run out of space! So check out the website!