Growing Crops Based On What Plants Need

Growers constantly regulate the temperature, humidity and lighting in their greenhouses to control crop growth as effectively as possible. Although the Netherlands is a global leader in measurement and control technology for greenhouse horticulture, there is still considerable room for improvement, says Leo Marcelis, Professor of Horticulture and Product Physiology at WUR. "One limitation of current control systems is that the greenhouse climate is measured at a single location using one sensor unit. Yet conditions are not the same throughout the greenhouse. Nor does this tell you whether those conditions meet the plant's precise needs at that moment."

Instead of monitoring the environment, it is better to use the plant itself as the starting point, Marcelis says. "If you know how active a plant is, you also have a better idea of what it needs. You can then use that information to control the greenhouse climate much more precisely. This could help growers save energy and reduce costs. At present, growers often build in a safety margin to prevent part of the greenhouse from becoming too cold or too humid, for example, which could lead to mould. Although this margin provides greater certainty about production, it also uses more energy than is strictly necessary. If you have a more precise picture of what a plant needs, you can use energy more efficiently without harming the crop. This could reduce costs and make greenhouse horticulture more sustainable."

Identifying what plants need and using that information to control the greenhouse climate is central to GreenControl. The project brings together Wageningen University & Research, Delft University of Technology, Eindhoven University of Technology and the University of Twente, as well as greenhouse builders, technology developers, growers and plant breeders. Together, they are investigating how a combination of sensors, cameras and algorithms can help monitor plant activity more effectively. Marcelis: "We hope this will give us a better picture of how a plant is doing at any given moment. The project focuses on tomatoes and lettuce, but the insights may also be useful for other crops, such as strawberries, cucumbers, sweet peppers and cut flowers. We are not so much investigating the specific needs of tomato or lettuce, but rather how best to identify what a plant needs."

Combining different technologies

Most of the technologies being tested by the GreenControl partners already exist, Marcelis explains. "The challenge is to use them in the right way and combine them effectively. They include sensors that measure photosynthesis, air movement and transpiration, as well as thermal cameras and cameras that track plant growth. We will test these technologies in different combinations. An important question is how accurate the system needs to be to be genuinely useful to growers. Too few measurements may provide an incomplete picture, while too many sensors make the system more expensive and complex. That is why we are looking at what can be measured with a limited number of sensors and cameras, as well as what is possible with a more extensive combination."

The researchers are also looking at the best places on the plant and in the greenhouse to position the measuring technology, Marcelis continues. "We also want to know how many plants we need to monitor per hectare to obtain a representative picture and how conditions vary across a greenhouse. And when a plant is less active, which factor or factors are responsible? Is it the temperature, the light, the humidity or a combination of these?" One challenge is ensuring that measurements remain reliable in a warm, humid greenhouse, where sensors and cameras can become dirty, shift position or begin to give inaccurate readings over time.

One of the project's goals is to reduce energy use by 25 per cent. The researchers are aiming for an even greater reduction in energy costs, at 35 per cent. This could be achieved not only by using less energy, but also by making smarter use of the available energy supply. Marcelis: "When it is sunny or windy, energy is often cheaper. Prices are also often lower on Sundays. By adapting cultivation accordingly, growers can save money while also reducing pressure on the electricity grid. An important question is how far we can go without compromising production, quality or plant health."

Turning data into control decisions

What Marcelis particularly hopes to achieve through the project is for growers to make greater use of smart plant-monitoring technologies and to use the resulting data more effectively. "You need not only to know how the plants are doing, but also to connect that information to greenhouse control. That is why GreenControl also looks at the advice provided by the system. Growers need to understand why the system recommends adjusting the heating, ventilation or lighting. Only then can growers develop confidence in the technology. That would pave the way for the next step: fully automated control. Before we can take that step, however, we first need to ensure that the system is robust."