Tomato grower uses ProJoules for harvest forcast

It is mid-March, and there is still a little wait for the first harvest at Kwekerij de Bron and Kwekerij de Maasroute. When is that first harvest expected? Week 15. Grower Dave van Drunen points to his computer screen. ProJoules is open on it. The cultivation plan on the screen clearly shows when the first kilos of plum tomatoes and loose, round tomatoes will be ready for harvest.

Dave runs both nurseries together with his brother Mike and father Jan. Once all the formalities are completed, he will also become the owner of the family business later this year. In total, they cultivate tomatoes on 7.3 hectares in Elshout. The total area is slightly larger, but the lowest greenhouse has been used as a caravan storage facility since 2020. From the moment the caravan storage was established, Mike has also been active in the family business.

Dave, Jan and Mike van Drunen

Planted later
At the tomato grower, planting was done later this year than in 2024. "In recent years, it was so dark during the initial phase of cultivation that we decided to start growing later this year. Normally, we plant after Christmas. This year, we planted after New Year, and in the other greenhouse not until January 23rd. We are just a bit short on capacity with our CHP (Combined Heat and Power), and we don't want to use the boiler to supplement, as it has become so expensive due to taxes and rising prices. That's why we started a bit later."

Since last year, the Van Drunen family has been growing rugose-resistant varieties, all from Axia. For the plum tomatoes it is Prunaxx XR, and for the loose, round tomatoes they have chosen Mediax XR and Joannax XR. Like many growers, the tomato growers in the south of the Netherlands still have to get used to the slightly different characteristics of the new, resistant varieties.

"My father describes the varieties as somewhat less easy to grow," Dave explains. "They are more challenging to manage under unusual climate conditions, for example, if it's colder or sunnier. We notice that the growth duration is a bit longer, and the yields are somewhat lower. However, the quality is really good. Four to five weeks after harvest, the fruits are still nice and firm." For the growers, who also handle their own packaging, this is an important aspect.

More accurate harvest forecasts
The switch to resistant varieties was a major change in 2024. Another change was that both nurseries transitioned from the cooperative Oxin Growers to The Greenery. This transition necessitated a third change for the growers. Dave explains how that works: "At The Greenery, they want us to provide a weekly harvest forecast for the entire year ahead. Normally, we would also provide harvest forecasts, but they were less far in advance and, in addition to data from our counts, were largely based on intuition."

To provide a more accurate harvest forecast, the growers looked for software that could assist them. Following a tip from their cultivation advisor, they started discussions with ProJoules. The crop planning platform is model-based, with light, or Joules, as its foundation. With ProJoules, growers can easily create cultivation plans.

Dave and the team of tomato growers use these cultivation plans to make production forecasts for the entire growing season. Previously, the growers were unable to do this and only provided short-term harvest forecasts. They did this based on plant measurements and their years of experience, assuming that a cluster is ready for harvest approximately eight weeks after it is formed. With ProJoules, the harvest forecast is more accurate, even beyond eight weeks. "In 2024, the long-term forecast in our cultivation plan with ProJoules matched quite well with what we actually achieved in practice."

© Thijmen Tiersma | HortiDaily.com
Dave looks at the latest state of the crop plan in ProJoules.

Plant measurements
During the season, the growers input plant measurement data weekly. This provides insight into the realization of the cultivation plan. Last year, Dave did this from behind the computer in his office. Since this year, it has been possible to enter the measurement data, such as head length, directly into ProJoules from a tablet. "I enter the same measurements as last year, but now not on paper, but directly from a tablet. This saves me time, and the advantage is also that I no longer have to do the calculations myself."

Dave demonstrates how, by selecting a tomato in ProJoules, the system calculates the setting for the grower. The platform takes stem density into account. For the growers in Elshout, the density is set at 2.7 for loose, round tomatoes and increases to 3.65 after pruning. For plum tomatoes, it is 4.05.

Despite the later start of the crops this season, Dave still expects to begin production around the same time as before. He can already see this in ProJoules. "We will start harvesting at a similar time as in 2024, also due to the longer growth duration of the new varieties."

Kwekerij de Bron and Kwekerij de Maasroute compare their harvest forecast data with fellow growers in a meeting organized by The Greenery. There, the growers from Elshout noticed that their actual harvest often aligned more closely with their forecast than those of their colleagues. This makes them satisfied with their new, more accurate harvest predictions.

© Thijmen Tiersma | HortiDaily.com
Dave takes weekly plant measurements

New insights
Meanwhile, the growers are also gaining new insights into their cultivation. The young grower considers this a nice bonus. In ProJoules' light plan, for example, it is easy to see how much light the crop needs and how much light is available. The amount of light that exceeds the crop's needs is highlighted in red. "This year, we have so far measured more natural light than what is outlined in our cultivation plan," Dave observes. He points to the computer screen, at one of the graphs in ProJoules. "For instance, in week 10 this year, we achieved 1360 joules. Last year, it was 900."

It was another dark winter, but in Elshout, it was less dark than last year. During times when there is a lot of light, growers can shade the light later in the season or apply chalk or coating to the greenhouse. Some ProJoules users decided to do more chalking or coating with the new insights. In Elshout, they do not chalk the greenhouse roof. "However, last year we did chalk the walls." An investment in a double screen in one of the greenhouses is planned for next year. "This year, we had AC film throughout the greenhouse."

© Thijmen Tiersma | HortiDaily.com View inside the greenhouse with one screen and a crop on perlite, with one plant in a rockwool block. Organic substrates were also tested last year. That made the crop even more vegetative. Something not preferred by the tomato growers.

Own variety profiles
In the crop planning platform, it is possible to create variety profiles. ProJoules offers growers these variety profiles as a standard feature, but growers also have the option to develop their own variety profiles. Dave says, "We are working with ProJoules to develop our own variety profiles. We notice that our current varieties have new specifications that we need to consider. Following a tip from our advisor, we have removed more leaves from the plant this year than before."

The current varieties also slightly exceed the standard growing degree days of the previous varieties cultivated in Elshout. "It takes a bit longer for the tomatoes to ripen," the young grower observes. The customers of the Brabant family business's tomatoes are also aware of this in advance, thanks to the more accurate harvest forecasting. This means they face fewer surprises during the season and can sell the tomatoes as effectively as possible.

Once all the tomatoes from the cluster have been harvested, Dave clicks on 'harvested' in ProJoules. This functionality helps track the actual harvest. Currently, it's only available for cluster tomatoes, but the functionality is also being developed for loose, round tomatoes.

For more information:
ProJoules
info@projoules.com
www.projoules.com