Name: Ben van Onna

Organisation: PTC+ ( Plus)

PTC+ is a Professional Practical Training Centre in the Netherlands that provides trainings for different sectors in the horticulture and agriculture, national as well as international.

For horticulture, the training centre offers an extensive package of training courses for example: greenhouse management, chain management, energy management, climate and water management, plant physiology, crop protection and post harvest.

Our concept is learning by doing.

Biography of Ben van Onna

Ben van Onna graduated in 1973 at Higher Horticultural Sc­hool in Utrecht

After that, he accomplished the teacher’s education Den Bosch successfully.

From 1975 until 1978 he worked as an instructor at CST (to-day PTC plus).

In 1978 he became an adviser for greenhouse vegetable growing, at first in service at the Ministry of Agriculture, the department Consultancy of Horticulture, later in a private Consultancy Office.

Since 1996 he is giving practical courses at PTC Plus, Ede as a tutor greenhouse climate control, plant physiology and energy management to growers and students, national as well as international.

The last few years he is also involved with T.O.T. (Training Of Trainers) programs for several National Training Centres worldwide.

Summary 1:

The importance of managing actual plant temperature:

Temperature is an important factor that influences plant processes.

If we talk about temperature, actually we have to consider the plant temperature.

Nowadays we have sensors at our disposal that can measure plant temperature.

By means of an infrared sensor it is possible to measure the average plant temperature on a spot of 10 – 15 m2. Several climate computers have the possibility to involve this measurement into the strategy.

In practice a lot of growers have this equipment but mostly use it for monitoring.

Temperature influences a lot of plant processes:

• The actual temperature, in combination with the actual CO2 concentration and light level, influences photosynthesis.

• A higher plant temperature rapidly increases respiration

• The average 24 -hour temperature influences plant development (flowering speed, growing speed etc.)

• The difference between plant and air temperature determines the level of transpiration but also can cause condensation.

• A temperature difference between leaf and fruit/flower influence the sugar transport inside the plant.

Essential questions are:

• To what extent does plant temperature deviate from the measured air temperature?

• Under what circumstances?

• What are the consequences and how can we manage the crop?

In this presentation I will explain aspects of plant temperature related to plant processes and how to apply it into the strategy.

Ben van Onna

PTC+, Ede

(The Netherlands)

Summary 2:

Improvement yields and quality by managing plant

Vegetative / generative balance:

To get an optimal production and a good quality it is important to get a good plant balance during the whole growing season. The right balance depends on the type of crop and the stage of the crop. Vegetable growers and cut flower growers are generally focussed on a high production and a good quality. Additionally, for example for rose growers the stem length is very important.

Pot plant growers are more focussed on the compactness and the flowering stage.

Since about 10 – 15 years several growers are using methods based on “crop recording”

They select some “count-plants” and registrate for example fruit setting, number of flowers, number and length of internodes, stem diameter in the top, plant load, growing period of a fruit/flower etc.

By putting these data in a computer bases system, making tables and graphs and comparing this with colleagues they learn how to interpret the balance of the crop and how to maintain plant balance.

What is a ‘vegetative’ and generative’ plant?

To see if a plant is ‘vegetative’ or ‘generative’ requires a good eye and some training.

We have to look at the top of the plant to see how the plant is growing at present.

Lower on the plant we can see how the plant has grown in previous weeks or months.

For short crops that do not produce flowers or compact plants, such as lettuce and several pot plants, it does not supply.

Plant balance is, simply said, the balance between leaves and fruits/flowers on a plant.

The principle can be used for fruit-producing crops as well as for flowering ornamental crops.

There must be a balance between production of sugars (source) en the demand for sugars

(sink).

Aspects of ‘vegetative’ and generative’ balance to be discussed:

• How to recognize generative or vegetative plants.

• What aspects play a role (e.g., greenhouse equipment, climate, irrigation, variety, plant stage, season, crop handling)

• What instruments does a grower have to steer the plant into the right balance to improve yield and quality.

Ben van Onna

PTC+, Ede

(The Netherlands)