ProDrain user group to be led by Applied Plant Research (PPO)

The ProDrain system which was introduced last year is now being used by a number of tomato and paprika growers. To get the most out of the system, a PPO-led user group has been set up to record the effects registered by the ProDrain system and study how these data can be used to improve greenhouse climate control.  The growers will convene once a month to compare their ProDrain measurement data. PPO will analyze the data in advance and focus on interesting phenomena during the meetings.

The ProDrain system accurately displays the growth and transpiration rate of the crop plants. In order for crops to be healthy, sufficient moisture needs to evaporate through the leaves (this process of releasing moisture by plants is called ‘transpiration’). During hot weather, plants use transpiration to keep cool.  Transpiration is also necessary, however, to stimulate the uptake of water from the roots, so nutrients are transported to the growing parts of the plant above the ground

HortiMaX has succeeded in developing an accurate method of measuring crop transpiration.  After mathematically filtering out any disturbances in the weighing tray data, ProDrain calculates the crop’s transpiration rate.  This calculation is used to generate a minute-by-minute representation of how the crop’s transpiration rate is reacting to the greenhouse climate. As a result, ProDrain offers extremely useful information for dedicated climate control. ProDrain sends the transpiration rate it has ‘measured’ to the climate computer, so it can adjust the climate setpoints accordingly. If the transpiration rate is too low, the computer can automatically raise the minimum pipe temperature, for example.

The plants in the ProDrain weighing gutter cover a few square metres of the greenhouse area, so they are sufficiently representative of the entire crop. ProDrain can be used for any hydroponically-grown crop. In addition to determining transpiration, ProDrain also measures the irrigation and drain volume, and the drain percentage achieved. ProDrain can even measure the growth rate of hanging crops, such as cucumbers and tomatoes.

The ProDrain measurements are displayed in graph format in Synopta. The graph above clearly shows how solar radiation (red line) affects transpiration (black line). In this case, the rate of transpiration in the morning slowly increases in relation to the radiation level. The crop’s growth rate (pink line), however, slows down as the transpiration increases, but recovers as soon as the transpiration starts to drop in the afternoon.

The graph also clearly shows how the humidity (green line) follows the pattern of transpiration: if transpiration is high, so is humidity and vice versa. This proves once more that high humidity has little bearing on a possibly too low transpiration rate.  As a result, control actions based on the measured transpiration rate are generally much more effective at stimulating transpiration (known as ‘activating the crop’) than those based on the measured humidity.