As a greenhouse grower you were always taught to create the best possible climate for your crop in order to achieve the desired production results. Of course it makes sense, and up to now, most growers have always been steering their crop from such a 'climate perspective'. But did you know that this approach is no longer the most effective nowadays? Present day technology allows growers to obtain direct feedback from their crop and include more factors to optimize the growing strategy. This so called 'crop control' approach enables growers to achieve even better results and grow even more efficiently.
Over the next couple of weeks we will take a closer look at the Crop Control approach in a special series of articles provided by HortiMaX. In these articles, product manager Joost Veenman takes a closer look at steering the crop with the ProDrain system. “The key to maximizing production is determining the exact needs of the plants,” says Joost in Part 1 of the series.

By Joost Veenman, HortiMaX:

To achieve the best results, commercial growers aim to keep the greenhouse conditions as comfortable as possible for the plants. 

But creating a comfortable climate and applying sufficient water won’t necessarily make the plants thrive. Two factors are essential in maximizing production: transpiration and photosynthesis (CO2 fixation). Many growers refer to this as plant activity.

To optimize photosynthesis, growers aim to maintain the ideal temperature, light and CO2 levels at all times. This requires these factors to be monitored constantly. The only problem is that it can be difficult to determine how the crop is responding. An essential piece of information is water transport through the plant. Water transports nutrients throughout the plant and allows the plant to cool itself through evaporation from the leaf surface (a process called transpiration). If the plant transpires more water than absorbed by the roots, the plant will close its stomata and growth will come to standstill.

Not surprisingly, growers are extremely interested in the actual water uptake and transpiration rate of the plants. What not many growers know, however, is that it has been possible to monitor these key values for some time now. A unique system, called HortiMaX ProDrain, is able to measure the exact quantities of water flowing to and from the plants in real-time. The first ProDrain systems were installed in 2006, and now the system is being used all over the world for a wide range of crops, such as tomatoes, cucumbers, peppers, strawberries and roses. ProDrain has become an established product for growers; not just a tool for developers and researchers.

How does it work?

HortiMaX ProDrain is a weighing system, which continuously measures the weight of the irrigation water, the drain water, the growing slab and the plants (the last-named in the case of hanging crops). The system keeps track of all fluctuations in weight. As measurements are performed every second, the system can detect the slightest change in weight and determine where the irrigation water has gone. Has it been absorbed by the plants or has it been turned into drain water? If the water isn’t inside the plants or it hasn’t left the plants as drain water, then the water must have been evaporated into the air.

The system also identifies and filters out larger weight variations caused by harvesting or maintenance work. This creates a closed loop of information, allowing the system to determine the plant transpiration rate in real time. In addition to measuring transpiration and water uptake, ProDrain can even monitor the growth rate of hanging crops. ProDrain can display the growth rate both as a real-time value in g/m²/hour or a cumulative value over the day in kg/m². Compared to systems that only monitor a single plant, ProDrain monitors a plant area of up to 8 m². This provides representative data for the entire crop.

Increased interest in crop transpiration

Recent research has revealed that reducing crop transpiration can lower greenhouse energy consumption significantly. However, to reduce crop transpiration safely and effectively, measuring the transpiration rate in real time is essential.

Transpiration, growth and radiation. Clearly visible, transpiration follows radiation but growth is a different process.

Fully automated irrigation based on water uptake

The desired amount of water in the growing slabs can be represented as the moisture content from 0-100%. The problem is that irrigation is applied in volume (e.g. litres) rather than as a percentage. By determining the saturation level in kg/m², it is possible to set the desired degree of saturation (or undersaturation) and control irrigation based on this value. In this way, the irrigation controller can automatically match irrigation application to the exact water uptake of the plants. This ensures that the moisture content of the growing slabs will never drop below the pre-set minimum level. Most ProDrain users now utilize the ‘ProDrain start’ as their preferred irrigation start condition, since it is the only method that actually takes into account the plants’ water uptake and can be used throughout the day.

More information? Stay tuned for part II of this article, which will be published on soon, or contact a HortiMax representative in your area:

North America :
Wil Lammers

Rest of the world:
Joost Veenman
Product Manager Climate & Energie

See also: to Hortidaily Article