The energy expenditure for staggered greenhouse tomato production would be twice as high as that of the current means of production with no appreciable increase in yield. Even so, the current means of production might benefit from LED lighting.
In Switzerland, hydroponic greenhouse tomato cultivation currently begins in January with pre-planting and ends in November with the last harvests. In northern Europe, tomato crops can be grown in a staggered fashion with an end-of-summer (September) planting and a final harvest in the following calendar year (August). Staggered production could potentially cover market demand year-round.
This study aims to determine whether there is an agronomic and financial benefit in introducing staggered production. In addition, the question of whether LED lighting would be beneficial in staggered production was also evaluated.
Specific needs of tomatoes
Tomatoes are plants that need large amounts of light and do not tolerate low temperatures. Because of this, they are potentially high consumers of energy.
One of the challenges of greenhouse cultivation is therefore managing and optimising energy costs vis-à-vis agronomic and crop performance (yield, quality, etc.).
In particular, longer production over the winter period will require more heating and lighting than over the summer. This energy consumption is mainly due to the heating of the greenhouses, but also to lighting, if there is any.
Three varieties of vine cherry tomatoes studied
The study focused on three varieties of vine cherry tomatoes particularly well adapted to the issue: DR0607, DR0564 and ‘Competition’.
The variety ‘Competition’ soon revealed numerous limitations (vegetative growth, growth pace, yield, etc.).
The first two varieties achieved yields 30–50% higher than ‘Competition’. In terms of vegetative growth, these two varieties were easily managed, with appropriate weekly elongations (26–29 cm/week) and stalk diameters, whilst ‘Competition’ exhibited excessively high weekly growth rates (32–35 cm/week).
Average yield increase of 20%
The effect of the artificial light was different for the three varieties. ‘Competition’ very quickly showed signs of burns due to the interline lights, which diminished its production potential. In general, the addition of light enabled an average yield increase of 20%, regardless of production type.
In terms of power consumption associated with heating, staggered production used 100% more energy than non-staggered production. This consumption surplus was not offset by a significant increase in yield. In non-staggered production, the addition of artificial lighting enabling the 20% increase in yields represented a cost of around CHF 8.00/m2. This cost must be compared with the additional 4 kg/m2 obtained with the DR0564 variety grown with lighting, which represents a financial gain of the order of CHF 12.00/m2 (at CHF 3.00/kg tomatoes). Finally, the use of interline LED lighting in addition to LED toplights failed to show an additional positive effect over the use of LED toplighting alone.
- In general, the addition of lighting enabled an average of about 20% increase in yield regardless of production type.
- In non-staggered production, a net profit of CHF 4.00/m2 (CHF 40,000/ha) was ultimately achieved with the artificially lit variant compared to the non-lit variant.
- In terms of power consumption associated with heating, staggered production used 100% more energy than non-staggered production. This consumption surplus was not offset by a significant increase in yield.
The overall energy cost of staggered production was ultimately measured at around 478 kWh/ m2 compared to 245 kWh/m2for conventional Swiss production, i.e. a difference of the order of 95%.
- The current fluctuation in energy costs must be considered in cost-efficiency calculations.