Kesgro's experiences with ProDrain and MM

Kesgro is a business with three glasshouses, each 22 acres in size, and is situated in Middenmeer, a town in the Dutch province of North Holland. Kesgro specializes in tomato production. Since recently, the business has been using a number of ProDrain systems and moisture meters (MM). We, therefore, caught up with Martin van der Hout, Kesgro’s general manager, to ask him about his experiences with this new equipment. 

Traditionally, growers irrigate based on the radiation level, drain water and time. Why do you believe that that these factors are not enough to determine the crop’s water requirement?

‘Water uptake is the result of many factors, not limited to only incoming radiation, but also include humidity deficit, lighting, etc. We aim to monitor the root environment throughout the day. Drain water is only a derivative of various water management factors.’

Why is the slab moisture level so important for growth?

‘Moisture affects the growth and development of the roots and, as a result, the growth and development of the crop, including the flowers and fruit. As a rule, the higher the moisture level, the higher the production, but it can also lead to weak, vegetative plants, with all of the negative implications this entails. Quite a few studies have been dedicated to this phenomenon.’

How do you measure the slab moisture level?

‘We have 8 valve sections in total, with 4 WCS and 4 ProDrains divided among them. As a result, each valve section is monitored by a MM or ProDrain. We also have 2 handheld moisture meters, which we use to measure the difference in slab moisture throughout the glasshouse and to determine whether the slabs of the MM and the ProDrain match the average.’

You now have 4 ProDrain systems, each with a 8m² crop/slab surface area. Does this adequately represent the entire glasshouse?

‘Yes, because the glasshouse is evenly sized. One of the drawbacks of using a scale is that it cannot be moved. If the head of a plant is broken, the scale will temporarily measure up to 5% less leaf area.’

A moisture meter is a point measurement. Does this provide you with enough information on the slab’s moisture content?

‘Yes, provided you use the MM correctly. I know there are large differences in moisture level at the point of measurement. This can be affected by the type of substrate and irrigation method used. The size of the irrigation cycle, irrigation frequency, etc., also play a role.’
What do you expect to gain from measuring the undersaturation level?

‘We need to learn how to work with it and trust it. I expect that the measurement will allow us to use the following setpoints:
• Additional irrigation cycle at night to correct finishing irrigation too early during the day.
• Night-time irrigation cycles between 3 a.m. and sunrise as a supplement after switching on the supplementary lighting around midnight. These cycles are always applied in combination with periodic cycles, combined with time and radiation.’

ProDrain also calculates crop transpiration. What is your experience with this variable and how do you expect to benefit from it?

‘We expect to gain a better understanding of climate and water management strategy. We also expect that it will allow us to improve our irrigation and climate settings.’

What do you expect to learn from the cumulative growth measurement?

‘What we first noticed is that growth is related to the amount of light that the crop is subjected to. What we are most interested in is the daily increase in the amount of dry matter. The measurement is, however, still very sensitive to the temperature and crop handling, for instance. When rehanging the plants, you have to make sure to re-attach that the same number of plants to the weighing system. We expect that the cumulative growth data will give us better insight into production and the effectiveness of our growing strategy.’

Do you still have insufficient data on the slab moisture at certain moments of the day?

‘We think we have enough slab moisture data now. I would, however, like to be able to better monitor the EC distribution inside the slabs.'


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