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French tomato grower Gilles Carriou switched last year to using RootmaXX cubes from Cultilene. This stone wool cube allows growers to extend the pre-planting phase to give more control over generative growth. The result? Benefits for both production and quality.
Gilles Carriou runs a greenhouse operation covering 2.6 hectares in the town of Lézardrieux in Brittany. This is where he grows Luminance-F1, a medium-sized vine tomato. He is part of the Prince de Bretagne group, a French grower cooperative whose members produce tomatoes over 180 hectares. A lot has changed at Carriou’s greenhouse operation, in 2015 he started heating with natural gas. ‘Until then, I used heavy fuel oil to heat my greenhouse’, says Carriou. ‘When natural gas became available, I managed to invest in a CHP plant that would decrease my energy costs and so allow me to expand my operations. We then constructed a greenhouse covering 1.3 hectares and installed a CHP plant with a capacity of 2.6 MW. Prior to this, I was using 160 kWh/m² to achieve a production of 50 kg/m². Now, with the CHP plant, I have a lot more heat available and it’s also cheaper. I’m now using 350 kWh/m². As you would expect, this is having a beneficial effect on production.
‘In 2015, Carriou also invested in a climate computer from Hoogendoorn which measures solar radiation levels, among other things. ‘This allows us a more precise control with regard to irrigation.’
More generative steering
In the autumn of 2016, the grower switched to RootmaXX cubes and Exact Air slabs, both from Cultilene. ‘I decided on RootmaXX because I wanted to extend the pre-planting phase; my idea was to leave the plants next to the planting hole for a longer period after receiving them so that I could achieve more generative control’, Carriou explains. ‘The RootmaXX cubes also have a good water buffer which makes extending the pre-planting phase easier. The unique X-fibre structure – a structure with fibres running in all directions – means that the roots keep rooting throughout the entire cube. Another advantage is fewer water roots at the bottom of the cube and more active roots in the upper layer. This allows the cube to be controlled very easily which also facilitates extending the pre-planting phase.’
To encourage generative growth, the grower waters each cube with 150 to 170 cc of irrigation water during the pre-planting phase; mainly during the night and morning. The plants were put onto the planting hole as soon as the third truss was fully in flower, from mid-November to mid-December. Carriou decided on Exact Air slabs measuring 90 cm long, 15 cm wide and 10 cm high. ‘Previously, I worked with slabs 7.5 cm high. With a slab 10 cm in height, there is less of a problem with Agrobacterium rhizogenes, the dreaded crazy roots. Also a larger substrate volume has advantages during the summer months.’
Optimum production and quality
After the plants were put onto the planting hole, Carriou reported that there was good and rapid growth of the roots from the cube into the slab. On advice from Cultilene, the grower adjusted his irrigation strategy: he reduced the dose size and increased the frequency. ‘Depending on the expected solar radiation, I keep the EC between 2.9 and 3.3 and programme the irrigation quantity and frequency accordingly. On June mornings, for example, when the weather is sunny, I provide 75 to 80 cc per cube every 15 minutes. The maximum water level is reached between 11:00 and 11:30 a.m. after which I increase the dose size to 150 cc until 1:30 p.m. Then, I change to 170 cc/cube per 80 joules of light.’
Carriou has been achieving good results since the middle of June this year, both with production and quality. ‘Production levels for the Luminance F1 variety are very high in the new greenhouse; I expect to harvest more than 65 kilos of vine tomatoes per square metre, of which more than 95% are of the ‘Extra’ class. Since April, we have actually been able to sell all of our tomatoes in this class, which means we are supplying a product of outstanding quality.’