NZ Grower - - CONTENTS - By Stefan Vo­grin­cic Phase 1: Phase 2: Phase 3:

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.grow­er2­ 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!

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