GB2036523A - Substrates for plant cultivation - Google Patents

Abstract

Soiless plant cultivation techniques have hitherto employed substrates such as foam panels through which the plant roots grow, mainly to develop on the underside of the panel. To promote root development in the substrate material itself, a method of soillessly cultivating a plant comprises growing the plant on a substrate which is provided with air passages. A substrate suitable for the cultivation of plants has air passages occupying from 5 to 40% of its volume, which air passages have cross sections of from 0.07 to 3.2 cm<2>.

Description

SPECIFICATION Substrates for plant cultivation The present invention relates to substrates for plant cultivation.

It is known that plants can be cultivated in the absence of soil on completely or partly artificial substrates which, in some cases are chemically neutral; such substrates have a relatively confined root space. This method of cultivation is known as soilless cultivation. As well as substrates which contain natural organic substances, such as peat or straw, it is also possible to use synthetic substrates, for example substrates formed from mineral fibres or foams based on polyurethanes and phenoformaldehyde resins.

Although these known substrate materials generally satisfy crucial requirements for soilless cultivation, such as being free from pathogenic bacteria and from substances harmful to plant growth, and having rapid and high permeability to water, root development within such substrates, often used in the form of panels, is not generally optimal. Thus most of the roots penetrate vertically through the substrates and develop on the underside thereof, which undersides generally rest on a support formed from a material which is impermeable to water. Contrary to what is actually required, only a few roots develop within the substrate material itself because the growth conditions there are not usually ideal as a result of the inadequate exchange of gases.

Although in the case of fully synthetic foam panels this disadvantage may be obviated by increasing the cell diameter of the foam pores, this is only possible to a limited extent because otherwise other properties which are relevant to the use of the material as a substrate would be adversely affected.

There is thus a need to provide substrates, for use in soilless cultivation, which promote the root development of plants actually within the substrate itself.

According to one aspect of the present invention, there is provided a substrate for the cultivation of plants which has air passages occupying from 5 to 40 /O of its volume, the air passages having cross sections of from 0.07 to 3.2 cm2.

The volume of the air passages is preferably from 10 to 20% of the volume of the substrate. The crosssection of the air passages, which may assume any shape for example, round, square, ellipsoidal or even irregular, is preferably from 0.5 to 1.2 cm2. It is preferred that the air passages extend completely through the substrate in use in a downwards direction i.e. that they are arranged in such a way that they extend, preferably substantially vertically, from the top to the bottom of the substrate, which is preferably in the form of a panel.

Another aspect of the invention provides a method of soillessly cultivating a plant which comprises growing the plant on a substrate which is provided with air passages, whilst yet another aspect provides the use of a substrate provided with air passages as a support for growing plants by a soilless cultivation technique. In each case the air passages preferably have a cross section of from 0.07 to 3.2 cm2.

It is also preferred that the air passages occupy from 5 to 40% of the volume of the substrate. Thus the method and use aspects of the invention preferably employ the substrates which are defined above.

In the cultivation of plants on substrates, preferably panels, provided with air passages in this way, it has been found that root development in the region between the substrate panel and the member supporting the panel is very much stronger than in the case of a panel which does not have air passages. In addition, more roots generally penetrate into the substrate material from below. The overall root mass of the plant has been found to be considerably increased compared with the root mass of substrate panels which do not have air passages.

This result is largely unaffected by the water retention behaviour of the substrates. Even substrates have only a slightly negative water retention value have been found to promote imposed root development when provided with air passages in accordance with the invention. An important factor in this respect is the cross-section of the air passages, which has to be optionally adapted to the par ticularsubstrate used.

The negative water retention value as used herein is understood to be that quantity of water which emerges in 30 minutes from a fully water saturated test specimen (length 220 to 230 mm, width 107 to 110 mm, height 70 to 80 mm) when that test specimen is freeiy stored in such a way that its longitudinal axis forms an angle of 60 with the horizontal.

The density and water absorption rate (as hereinafter defined) of the substrate have been found to play only a minor part in improving root development.

However, it is preferred that the degree of water absorption of the substrate is greater than 75% by volume over a period of less than 10 minutes. The water absorption rate is determined on a test specimen of substrate material (length 220 to 230 mm, width 107 to 110 mm, height 70 to 80 mm) which is placed on the surface of distilled water at 20"C; the time taken by the test specimen to become fully saturated with water so that it appears completely wet is then measured, as is the amount of water absorbed which is determined by differential weighing. From these two measurements the water absorption rate may readily be calculated.

It has also been found to be of advantage to provide the substrates on their underside (in use) with profile passages which connect the downwardly extending air passages. The underside of the panel is understood to be that side which rests on the supporting member in use. The profile passages on the underside of the panel may be situated for example either directly above the supporting member or substantially parallel thereto, preferably at a distance of up to about one centimetre from the surface of the supporting member.

Preferably, these profile passages connect from 10 to 45% of the downwardly extending air passages, which may comprise perforations, to one another. It is preferred for them to have a cross-sectional area which is from 50 to 100% of the cross-sectional area of the air passages.

The air passages (or perforations) and the profile passages which may be additionally provided on the underside of the panels may be formed in known manner, for example by punching, milling, drilling, piercing or cutting, depending on the type of substrate material used.

Suitable substrate materials are any of the known substrates for soilless cultures, for example those formed from mineral wool, mineral fibre, peat, and fully synthetic foams such as those based on polyurethanes and phenolic resins e.g. phenolformaldehyde resins.

The following Examples and Comparison Examples illustrate the invention.

EXAMPLE I (Comparison Example) Young melon plants were used for this Example and all the following Examples. The plants had been grown in standard soil P in polyurethane pots with a hole in the bottom. The pots had a diameter of approximately 10 cm. When the plants were about 200 cm tall and their roots were growing out of the pots (i.e. after about four weeks), the pots were placed on substrate panels of phenolic resin foam resting on a water-impermeable film.

The panels were connected to a drip watering system with two drips to each plant. The plants were supplied with nutrient solution through the drip watering system three times a day for between 5 and 10 minutes, corresponding to between 1.5 and 2.5 litres of nutrient solution per plant per day. The roots of the plants penetrated into the substrate and the vertical growth of the plants was guided by tying them to strings. At a height of 1 metre, the plants were supported. The side shoots were supported after development of the first or second leaf on the shoot After about 2.5 months, 1 or 2 melons weighing from 1.2 to 1.5 kg were collected from each plant. After picking of the melons, the various substrate panels were inspected for root development.

A substrate panel of phenolic resin foam having a density of 19.5 kg/cc was used for this Comparison Example. Its water absorption rate was 5 minutes, 20 seconds and its negative water retention was 31 cc.

The panel was not perforated.

The few roots of the plants grew through the panel. The underside of the panel showed only moderate root development. These roots showed little or no repenetration into the substrate material.

The plant pots were easy to remove from the panel orfell off it.

EXAMPLE 2 A phenolic resin foam panel formed from a foam having the same physical properties as that used in Example 1 was used to repeat the procedure of Example 1. However, the panel was perforated from top to bottom with 8 mm diameter holes. The interval between the perforations was about 20 mm.

With this panel, the roots projected vertically therethrough in the perforations. The underside of the panel showed vigorous root development, with the roots growing back into the perforations from the underside. Relatively vigorous root development was visible in 60 to 70% of all the perforations. At the end of the experiment the plant pots could only be dislodged from the substrate surface by force.

EXAMPLE 3 The procedure of Example 1 was followed using as substrate a foam panel which had the same physical properties as the panel of Example 2, i.e. it was also perforated. However, this panel had been produced in such a way that its eluate had a pH-value of 6.4. In all the other Examples, the eluate had a pH-value of from 5.3 to 5.4.

The pH-value of the eluate was determined as follows: A 250 cc glass beaker was filled with 140 cc. of distilled water and a cylindrical foam test specimen 65 mm long and 50 mm in diameter was placed with one of its flat ends on the surface of the water. After the test specimen has become fully saturated with water, it was left in the glass beaker for 30 minutes. It was then wrung out and the pH-value of the water discharged was measured in known manner (for example with indicator paper or a pH-meter).

In this substantially neutral panel, after following the procedure of Example 1, root development was found to have been as good as in Example 2. It was relatively vigorous in 70 to 80% of all the perforations.

EXAMPLE4 (Comparison Example) A non-perforated phenolic resin foam panel was used in the procedure of Example 1. The panel had a density of 21 kg/m3,a very high water absorption rate (1 minute, 5 seconds) and a very high negative water retention (610 cc) and, hence, a rapid water release.

In this panel, root development was found to have been as poor as in Example 1. Only a few roots had penetrated into the panel and the underside of the panel showed only weak root development. The plant pots fell off the substrate or were easy to dislodge therefrom.

EXAMPLE 5 Phenolic resin foam panels having physical properties corresponding to the panel of Example 4 were perforated from top to bottom with 3 mm diameter holes. The perforations were made at intervals of about20 mm.

After the melon plants had been cultivated on these panels by the procedure of Example 1, it could be seen that their roots had grown vertically through the panels, for the most part in the perforations.

Some cross root development had occurred in the perforations. The main root mass was on the underside of the panels. The plant pot were bound relatively firmly to the substrate panel by the vertical roots.

EXAMPLE6 (Comparison Example) Very low-density (d = 16.1 kg/m3) phenolic resin foam panels were used in carrying out the procedure of Example 1.

The water absorption rate of the panels was 2 minutes, 30 seconds and their negative water retention 90 cc. The panels were not perforated. After cultivation of the melon plants, it was found that their roots had grown vertically through the panels. There was also fairly vigorous root propagation on the underside of the panels. The plant pots were firmly bound to the substrate panel by the roots.

EXAMPLE 7 Example 6 was repeated with the difference that the phenolic resin foam panels were perforated with holes 3 mm in diameter at intervals of about 20 mm.

Root development was as good as in Example 6. In addition, however, roots had penetrated into the perforations from below.

The Examples show that substrate panels formed with air passages promote root development and root growth to a greater extent than that obtained by a reduction in panel foam density and/or a change in the panel foam negative water retention value.

Claims (27)

1. A substrate for the cultivation of plants which has air passages occupying from 5 to 40% of its volume, the air passages having cross sections of from 0.07 to 3.2 cm2.

2. A substrate according to claim 1 which has air passages occupying from 10 to 20% of its volume.

3. A substrate according to claim 1 or 2 in which the air passages have cross sections of from 0.5 to 1.2 cm2.

4. A substrate according to any one of the preceding claims which has a water absorption rate (as hereinbefore defined) of 75% byvolume/ < 10 minutes.

5. A substrate according to any one of the preceding claims which has air passages extending completely thereth rough, in use in a downwards direction.

6. A substrate according to claim 5 which is provided with profile passages which in use of the substrate extend through the underside thereof to conneck the downwardly extending air passages.

7. A substrate according to claim 6 wherein the profile passages connect from 10 to 45% of the downwardly extending air passages.

8. A substrate according to claim 6 or 7 wherein the cross sectional area of the profile passages is from 50to 100% of the cross sectional area of the air passages.

9. Asubstrate according to any one of the preceding claims which is formed from a mineral wool or mineral fibre.

10. A substrate according to any one of claims 1 to 8 which is formed from peat.

11. A substrate according to any one of claims 1 to 8 which is formed from a synthetic foam.

12. A substrate according to claim 11 wherein the synthetic foam is based on polyurethane or a phenolic resin.

13. A substrate according to any one of the preceding claims when in the form of a panel.

14. A substrate according to claim 1 substantially as described in any one of Examples 2,3,5 and 7.

15. A substrate according to claim 1 substantially as hereinbefore described.

16. A method ofsoillesslycultivating a plant which comprises growing the plant on a substrate which is provided with air passages.

17. A method according to claim 16 in which the air passages have a cross sectional area of from 0.07 to 3.2 cm2.

18. A method according to claim 16 or 17 wherein the air passages occupy from 5 to 40% of the volume of the substrate.

19. A method according to claim 16 substantially as described in any one of Examples 2,3, 5 and 7.

20. A method according to claim 16 substantially as hereinbefore described.

21. A plant or any part thereof when grown by the method according to any one of claims 16 to 20.

22. The use of a substrate provided with air passages as a support for growing plants by a soilless cultivation technique.

23. A use according to claim 22 wherein the air passages have a cross sectional area of from 0.07 to 3.2 cm2.

24. A use according to claim 22 or 23 wherein the air passages occupy from 5 to 40% of the volume of the substrate.

25. A use according to claim 22 substantially as described in any one of Examples 2,3, 5 and 7.

26. A use according to claim 22 substantially as hereinbefore described.

27. A plant or any part thereof when grown in accordance with the use of any one of claims 22 to 26.