PREFACE

I have gladly accepted the invitation to open this 4th Symposium organized by the Working Groep "Peat in Horticulture". This working group was at the time instituted by the Commission on Plant substrates" of the International Society for Horticultural Science.

It gives me - as representative of the Dutch Ministry of Agriculture and Fisheries - great pleasure, to welcome you all today, and I should like to give a special word of welcome to the foreigners among you. We, - as Dutchmen -, highly appreciate it that the Commission on Plant substrates of the International Society for Horticultural Science (I.S.H.S.) has decided to hold this Symposium in this country.

The central subject matter of your Symposium will be "Peat and its use in horticulture", but attention will also be paid to other products which are used in combination with peat and also to the so-called artificial substrates.

The use of peat and peat-products has already for a long time been of importance for the improvement of the physical qualities of the natural soils, both the light sandy soils and the heavy clay soils. This form of soil improvement can even be economically justified in intensive cultures in the open. Besides, it is especially the growth of young plants and the complete cultivation of plants in well-directed composite substrates, which have become of great importance. Because of this we have become independent of the natural condition of the soil and have got the conditions, desirable for the growth of the vegetation, far better under control. Formerly, plant substrates were specially used for the growth of plant material and for the cultivation of pot plants in floriculture. But we also see that crops are more and more fully cultivated in special substrates. This applies to both vegetable growing and the cultivation of flowers under glass, and also to the cultivation of ornamental arboricultural crops in pots or containers. And, of course, also to mushroom growing, already known in olden times. It may be interesting to you to know more about the importance of the different branches of horticulture in the Netherlands, where plant substrates are used to an increasing extent and for some crops even up to 100%. I shall express the importance of these brances of horticulture by the annual production value, quoted in millions of guilders.

This production value in the Netherlands is as follows:

- vegetable growing under glas about	775	million	guilders
- cut flowers	950	"	"
- pot plants	150	"	"
- arboricultural products	190	"	"
- mushrooms	80–90	"	"

The total production of pot soils in the Netherlands is now more than 500,000 m³.

Advantage of the growth of plants in substrates

I have already observed that the methods of growth in substrates has the advantage that conditions, desirable for plants cultivation, can be held much better under control. The air and water supply to the physical root environment can be made as optimally as possible and plant nutrition (fertilizers) can be better regulated, depending on the stage of development of the crop.

When growing plants in containers or in substrates above the soil in glasshouse, it is far easier to give the crops the most desirable soil and root temperatures. In this way we can save a great deal of expenses on the costs of energy for soil heating which are very high these days. But it will be necessary that research will give more insight in the optimal root and soil temperature for our important glass-house crops.

Another important advantage of the growth in substrates is, that we are becoming independent of plant diseases which may remain in the soil. This specially applies to carnations, tomatoes and cucumbers in which parasitic fungi in soils, such as Phialophora, various Fusarium species and nematodes, play a role of importance.

Finally, I would mention an interesting aspect of the growth of woody ornamental plants and perennials on substrates in containers. This unables us in our climate to deliver these plants throughout the year, so, also during the summer half-year. This is of great importance for garden-amateurs and others.

International standardization

Now that so many scientists in plant substrates are meeting here on international level this week, I want to draw special attention to three aspects of standardization, which, - if possible on international level - should be realized in the future.

These three aspects are:

1. Standardization of the production process of "plant substrates". This concerns a regulation for the nature of the composite parts, the relative proportions of weight or volume, and the right method of mixing. Based on research carried out so far, we could, in this way, come to a limited number of plant substrate-mixtures. Depending on the purpose, - so the crop for which they are destinated - they could be prepared according to a standard method.
2. Standardization of methods to determine the physical qualities, both of starting material for substrates and final product.
3. Standardization of methods of chemical determination where the nutrients and where any harmful chemical substances are concerned.

This standardization of the physical and chemical qualities of plant substrates, will also provide for objective criteria of quality. These are also essential if we want to take legal measures to protect consumers of pot plants and of plant substrates. From what I hear, this subject will be discussed in your Symposium on next Thursday, 10th April.

Ladies and gentlemen,

As horticultural scientists we are glad that we have an International Society for Horticultural Science. This Society is a living and active organization, testifying the many years' activities of all the international commissions and working groups, specialized in the different branches of Horticultural Science.

I hope you will have a good symposium and express the wish, that the mutual exchange of knowledge and experience will enrich you, and will be a stimulus to all participants, to carry on their activities in "research and development" in the interest of the development of horticulture in all our countries.

I wish you success with the many excursions which are on the programme and a pleasant stay in this country. I hope, that apart from the specialized subject of this Symposium, you will also get some ideas of Dutch horticulture and of the Netherlands in general. May your excursions be favoured by good spring weather and a dazzling sunshine!

And with these good wishes on behalf of our Ministry of Agriculture and Fisheries I open this Symposium.

Ir. P.J. Stadhouders
Inspector of Horticulture
Ministry of Agriculture and Fisheries
The Hague, Netherlands