GB1600481A

GB1600481A - Process for growing plants

Info

Publication number: GB1600481A
Application number: GB1636/77A
Authority: GB
Original assignee: Fisons Ltd
Current assignee: Fisons Ltd
Priority date: 1977-01-15
Filing date: 1977-01-15
Publication date: 1981-10-14
Also published as: BE862762A; DK17178A; AU3237878A; FI780107A; FR2392597A1; JPS5392230A; NL7800280A; IT7819270A0; IT1109815B; DE2800889A1; IL53788A0; SE7800438L

Description

(54) PROCESS FOR GROWING PLANTS (71) We, FISONS LIMITED, a British Company, of Fison House, 9 Grosvenor Street, London WIX OAH, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a process and composition, notably for use in the growth of plants.

It has been proposed to grow plants with their roots immersed in a flowing film of liquid containing plant nutrients. Typically, a shallow waterproof trough is formed and a film of aqueous plant nutrient flows through the trough, is collected and recycled, e.g. to a header tank from whence it is fed back to the trough. Such a plant growth system is called hereinafter a nutrient film technique or NFT system.

During the cycle, water and nutrients are taken up by the plant and these require replacement before the nutrient solution is recycled. Control of the nutrient addition is achieved by addition of water in response to a level sensor, addition of nutrient in response to a conductivity sensor and addition of acid in response to a pH sensor since the circulating nutrient solution becomes progressively more alkaline. In practice it is difficult to ensure uniform constitution of the circulating nutrient system and temporary major variations in the composition occur. Furthermore, after a period of operation, plants growing in such an NFT system die back even though it appears from the control sensors that the solution contains adequate nutrients. The cause of this die back has not hitherto been identified. In order to rectify the dying back it has become conventional to bleed off part of the nutrient solution to waste rather than recycle it and to make up the lost liquid by adding fresh water. Alternatively, the whole system is drained down, flushed out with fresh water and then fresh nutrient solution is cycled around the system. However, both these operations are wasteful in water and nutrient and cause a check in the plant growth by subjecting the plant to sharp changes in environment.

Whilst the above problems have been realised by those engaged in nutrient film techniques, they have been accepted as inevitable. Attention has been directed toward minimising their effect by improving the monitoring of the nutrient composition.

We have now found that the above problems are caused by the build up of chemicals which are not consumed or which are only slowly consumed by the plant (for convenience hereinafter denoted nonnutrient chemicals) in the solution. The conductivity sensor does not distinguish non-nutrient chemicals from other nutrient chemicals which are more rapidly consumed and the concentration of the nonnutrient chemicals can build up to such a level that the conductivity sensor no longer activates the feed of nutrient chemicals to the system, causing a check in the plant growth.

We have found that the above problems can be reduced by feeding nutrients to the system in amounts which are in direct proportion to the amount of water that is fed to the system. This ensures that, even though the level of non-nutrient chemicals may build up, further nutrients are added to the system whenever water is added to the system. By using this system for feeding the nutrient chemicals it is possible to operate a nutrient film technique for long periods without the effects of an accumulation of non-nutrient chemical becoming apparent.

Also, the nutrients are fed to the system in a fixed proportion to one another and this tends to reduce the development of gross imbalances in the system. It is thus possible to maintain the plants in a more uniform environment than hitherto and to reduce the amount of water and/or nutrient solution wasted.

The term main nutrient chemical is used herein to denote plant physiologically acceptable ions or compounds containing nitrogen, phosphorus, potassium, calcium, magnesium or sulphur in which these elements are available to the plant. The term nutrient hereinafter denotes collectively both main nutrient and nonnutrient chemicals. It will be appreciated that water is essential for plant growth and is specifically excluded from the above definitions of main and nonnutrient chemicals.

Accordingly, the present invention provides a process for growing plants using a nutrient film technique characterised in that a nutrient solution is circulated in a system, the volume of circulating solution is monitored and is maintained at the desired level by the addition of water, and nutrients are fed to the circulating solution in an amount directly proportional to the amount of water fed to the solution. The invention also provides a trough in which plants are adapted to grow and through which a nutrient solution is adapted to be circulated, means for circulating the nutrient solution through the trough and means for feeding nutrients and water to the solution, the nutrient feed means being adapted to feed nutrient solution in an amount which is directly proportional to the amount of water fed to the circulating'solution.

The proportionation of the feed of nutrient to the water feed may be achieved in a number of ways. Thus, a concentrated nutrient solution is fed to the nutrient solution circulating in the NFT system by a proportionating pump which relates the feed of concentrate to the rate of feed of water. Alternatively, nutrient concentrate may be mixed with part or all of the water to be fed to the NFT system to provide the desired diluted solution. For example, the water fed to the NFT system can pass through a venturi section and draw concentrate into the water at the venturi from a reservoir. Other methods for achieving proportionation of the nutrient feed can be readily devised.

The nutrients are added to the solution circulating in the NFT system either directly (in the form of an aqueous solution or concentrate) or indirectly via a mixing tank in which they are dissolved in part or all of the water to be fed to the NFT system. It is preferred to incorporate acid into the nutrient mixture to provide a storage stable solution which is fed directly to the circulating nutrient solution to make up both water and nutrients lost to the plant, or to provide a storage stable concentrate to be added to the circulating nutrient solution in proportion to the water which is added to make up water lost to the plants.

Whilst it will normally be preferred to incorporate sufficient acid into the nutrient solution or concentrate to give a mixture having the desired pH, it may be desired to monitor the pH of the circulating nutrient solution as a safety measure and to add some of the acid separately. The presence of the acid reduces the problems of scale and precipitate formation, notably in hard water areas, caused by phosphates.

The main nutrient chemicals for present use include for example potassium and/or magnesium and/or calcium nitrates: potassium phosphates, e.g. KH2PO4; potassium hydroxide; and/or potassium and/or magnesium sulphates. It is preferred that the water fed to the system provide the necessary calcium for the plants. Therefore, it is preferred that the mixture be substantially free from calcium salts, e.g.

contain less than 1% Ca by weight on the dry weight of the mixture. Desirably the nutrients are substantially free from nonnutrients chemicals, e.g. halogen and sodium; i.e. contain less than 5% of such salts on the total nutrient chemicals by dry weight. It is also preferred that the nutrient chemicals provide N, P and K in the following weight ratios 1-7:1:3-13.

Where the mixture also contains a mineral acid, this is preferably free nitric acid, but other free mineral acids, e.g.

phosphoric acid, or mixtures of acids may be used. The amount of acid used is preferably sufficient to provide a pH of less than 2, e.g. from 0.5 to 1, when the mixture is dissolved in water to form a concentrate for storage and transport. Such a concentrate will provide a pH of 1.5 to 4 when the mixture is dissolved in water to the desired concentration for addition to the trough. Typically, this will require the equivalent of at least 15 parts, e.g. 15 to 35 parts, by weight of nitric acid per 100 parts by dry weight of the nutrient mixture.

However, in some cases the presence of all the acid in the nutrient mixture may be undesirable, e.g. when the hardness and/or the pH of the water fed to the NFT system changes frequently. In such cases the presence of the acid in the nutrient mixture or solution may cause excess acidity in the solution in the NFT system if the nutrient concentrations are maintained at the desired levels. We therefore prefer to feed part or all of the acid as a separate feed from the nutrient, but also proportionated to the water feed.

The acid usually provides the majority of the P as phosphoric acid and desirably some of the N as nitric acid. Typically, the acid is a mixture of nitric and phosphoric acids providing N and P in weight ratios of 1:3 to 1:5, optionally in admixture with calcium nitrate. The relative proportions of nutrient and acid fed to the system may be varied.

Accordingly, the present invention provides a method for growing plants in a nutrient film system which comprises feeding water to the system in response to a level sensor in the system; feeding to the system nutrients in an amount directly proportional to the amount of water fed to the system; and feeding a separate supply of acid to the system in proportion to the water fed to the system.

If desired the addition of the acid may be overridden by a pH sensor where, for any reason, the acidity of the solution was already high. If desired, a yet further separate feed of acid, e.g. of nitric acid, can be provided to feed acid in response to a pH sensor to supplement the N,P acid'feed in cases where excessively hard water is used.

In addition to the main nutrients and acid, the mixture of nutrients for present use may contain other ingredients, e.g. trace metals (notably copper, molybdenum, zinc, manganese, iron or boron), dyes, pesticides (e.g. algicides, fungicides or insecticides), wetting agents or emulsifiers etc. Where an acid is present in the mixture, it is usually not necessary for there to be present a sequestering agent as has often been considered essential with prior art mixtures.

The invention will now be exemplified using the system shown in the accompanying drawing which is a diagrammatic flow chart of an NFT system.

A shallow trough 1 is formed, e.g. from polyethylene sheeting, preferably with a slight fall so that nutrient solution flows through the trough. If desired the floor of the trough is ribbed. to subdivide the width of the trough where several rows of plants, e.g. carnations, are to be grown in one trough. Preferably, the floor of the or each, trough is provided with capillary matting or other similar material to spread the nutrient solution across the trough.

Nutrient solution is provided from a header tank 2 provided with a wier overflow 3 or other means for maintaining a constant head of solution in tank 2. Preferably, the nutrient solution flows from tank 2 to trough 1 under gravity, although it may be pumped if desired.

Trough 1 discharges nutrient solution to a sump tank 4. Sump tank 4 is provided with a liquid level sensing device 5, e.g. a ball cock or a float type contact switch, which actuates a valve or pump means 6. A nutrient solution is provided in a storage tank 7 and feeds valve or pump means 6.

Tank 7 holds a concentrate which requires dilution before use, and pump or valve means 6 incorporates a proportionating means whereby the rate of feed of nutrient is related to the flow of diluent water, which may flow to tank 4 via means 6 or separately. Tank 4 is also provided with a pH sensor 8, e.g. a glass/calomel electrode assembly, and a reservoir 9 for acid where it is desired to add acid in addition to the nutrient solution in tank 7. Tank 4 is also provided with a conductivity sensor 10 to monitor the nutrient level; and with a stirrer to ensure mixing of the contents of tank 4.

Where it is desired to add calcium separately from the main water, nutrient or acid feeds, calcium nitrate solution may be added from reservoir 11 via a pump or valve means 12 incorporating means for relating the addition of calcium nitrate to the addition of water.

Example I e The above system Is operated using a proportionated feed of water and nutrient to the trough, nutrient solution being fed, e.g.

by pump, to tank 2 from tank 4. Excess solution overflows wier outlet 3 and returns to tank 4. Nutrient solution flows through trough 1 where part is picked up by plants growing in the trough, and then to sump tank 4. Consumption of water and nutrients by the plants causes the level in tank 4 to drop, thus actuating sensor 5. This initiates the feed of replenishment nutrient and water via means 6. The pH sensor and the conductivity sensors were not used to control the addition of water or nutrient.

Such a system was operated for 6 months for the growth of tomatoes in troughs 15 cms wide and 25 metres long. Tomato plants were placed with their roots spread out over capillary matting in the trough at 45 cm spacings. A nutrient solution containing 100 ppni N,200 ppm K and 50 ppm P was prepared using hard water (70 ppm Ca) and contained 45 ppm of N as free nitric acid.

This solution had a pH of about 2 and was fed at approximately 1.5 litres per minute to trough 1. The solution showed no tendency to form precipitates in tank 2 or elsewhere in the system.

The nutrient solution returning from trough 1 to sump tank 4 was analysed for nutrient content and pH at intervals throughout the trial. The nutrient levels remained at all times in the range 90 to 100 ppm N,125 to 150 ppm K and 140 to 160 ppm P and the pH was at all times in the range 6.0 to 6.5.

The above system operated for the 6 month period with excellent plant and fruit growth without the need to bleed off nutrient solution or to flush out the system due to the deleterious effects of salt build up or imbalance.

By way of comparison, when a conventional nutrient film technique was used, it was necessary to use a pH control system and acid feed; a conductivity sensor and two separate nutrient feed systems one for the majority of nutrients, the other for the calcitic nutrients); and a water level sensor and feed system. The nutrient solution caused precipitation in the storage tank and elsewhere in the system, notably in sump tank 4. Also, the nutrient levels in the circulating nutrient solution returning from trough 1 to sump tank 4 varied by as much as 30% and the pH varied by as much as 1.5 units about the desired values.

After 8 weeks this comparative system had to be flushed out with fresh water and refilled with nutrient solution to prevent regression of the plants due to salt build up despite the fact that the conductivity sensor was indicating an apparently high level of nutrient salts.

WHAT WE CLAIM IS: 1. A process for growing plants using a nutrient film technique characterised in that a nutrient solution is circulated in a system, the volume of circulating solution is monitored and is maintained at the desired level by the addition of water, and nutrients are fed to the circulating solution in an amount directly proportional to the amount of water fed to the solution.

2. A process as claimed in claim I wherein a concentrated nutrient solution is fed to the nutrient solution circulating in the NFT system by a proportionating pump which relates the feed of concentrate to the rate of feed of water.

3. A process as claimed in claim 1 wherein nutrients are mixed with part or all of the water to be fed to the NFT system to provide an aqueous solution of nutrients which is fed to the circulating solution.

4. A process as claimed in any one of the preceding claims wherein the nutrients provide N, P and K in the circulating solution in weight ratios of 1-7:1:3-13 respectively.

5. A process as claimed in any one of the preceding claims wherein at least part of the N and P in the mixture of nutrients fed to the circulating solution is provided by a free mineral acid.

6. A process as claimed in claim 5 wherein the feed of part or all of the acid to the circulating solution is controlled separately from the other nutrients containing the N and K.

7. A process as claimed in either of claims 5 or 6 wherein the acid is a mixture of phosphoric and nitric acids.

8. A process as claimed in any one of claims 5 to 7 wherein calcium nitrate is admixed with the acid.

9. A process as claimed in any one of claims 5 to 8 wherein the rate of feed of acid with respect to the rate of feed of other nutrients is variable.

10. A process according to claim 1 substantially as hereinbefore described.

11. A process according to claim I substantially as hereinbefore described in the Example.

12. A kit of parts for use in the process of claim 1 comprising a trough in which plants are adapted to grow and through which a nutrient solution is adapted to be circulated, means for circulating the nutrient solution through the trough and means for feeding nutrients and water to the solution, the nutrient feed means being adapted to feed nutrient solution in an amount which is directly proportional to the amount of water fed to the circulating solution.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. ppm P and the pH was at all times in the range 6.0 to 6.5. The above system operated for the 6 month period with excellent plant and fruit growth without the need to bleed off nutrient solution or to flush out the system due to the deleterious effects of salt build up or imbalance. By way of comparison, when a conventional nutrient film technique was used, it was necessary to use a pH control system and acid feed; a conductivity sensor and two separate nutrient feed systems one for the majority of nutrients, the other for the calcitic nutrients); and a water level sensor and feed system. The nutrient solution caused precipitation in the storage tank and elsewhere in the system, notably in sump tank 4. Also, the nutrient levels in the circulating nutrient solution returning from trough 1 to sump tank 4 varied by as much as 30% and the pH varied by as much as 1.5 units about the desired values. After 8 weeks this comparative system had to be flushed out with fresh water and refilled with nutrient solution to prevent regression of the plants due to salt build up despite the fact that the conductivity sensor was indicating an apparently high level of nutrient salts. WHAT WE CLAIM IS:

1. A process for growing plants using a nutrient film technique characterised in that a nutrient solution is circulated in a system, the volume of circulating solution is monitored and is maintained at the desired level by the addition of water, and nutrients are fed to the circulating solution in an amount directly proportional to the amount of water fed to the solution.

10. A process according to claim 1 substantially as hereinbefore described.