AU3505999A - Agent for regeneration of growing media and inhibition and removal of build ups and sediments in water systems used for plant nutrition - Google Patents

Description

AUSTRALIA

Patent Act 1990 COMPLETE SPECIFICATION STANDARD PATENT .o* o* 1 0 AGENT FOR REGENERATION OF GROWING MEDIA AND INHIBITION AND REMOVAL OF BUILD UPS AND SEDIMENTS IN WATER SYSTEMS USED FOR PLANT NUTRITION The following statement is a full description of this invention, including the best method of performing it known to us: Inventors: Jan Teren, Bratislava (SK) Charles Chromicky, Sydney, (AU) Agent for regeneration of growing media and inhibition and removal of build ups and sediments in water systems used for plant nutrition.

This invention relates to an agent for regeneration of growing media and inhibition and removal of built ups and sediments in equipment and piping used for application of water and water solutions of plant nutrients related to soilless hydroponic growing of plants as well as in irrigation systems, especially if they are combined with application of plant nutrients.

In soilless hydroponic growing of plants, in irrigation and fertigation 10 through various systems, especially in summer conditions and when using water of higher salinity, the equipment and its parts (drippers, valves, small diameter tubes) become partly or totally blocked by salt build ups, and the functionality of the system is considerably reduced.

*The reason for this is continuous buildup of calcium, magnesium, iron and 15 manganese compounds brought in by water and plant nutrition substances.

The continuous blockage of the piping will cause a reduced flow or even a discontinued flow of water or the nutrient solution. This will disable full development of the plants.

Extensive growing of plants by hydroponic cultures is associated with life :span of the growing media. Long term experience shows that using the same medium for an extensive period of time results in lower yields. This phenomenon is called "aging of the medium". The cause is accumulation of salts on the media surfaces. This has its origin in the exchange of ions in the system: plant-medium-nutrient solution. Jermakov, E.I. (1975) showed, that a long term utilization of a medium is associated with a disturbance of its silicon components and resultant freeing of silicon and aluminium compounds. Orthosilicic acid generated in this process and finely dispersed particles of calcium, magnesium, aluminium and iron stick to the surface of plant roots and suppress plant growth. Equally, in the process of a long term utilization of a medium, the nutrient solution at the surface is drying out through surface evaporation, leaving the surface covered with crystallized less soluble salts. The degree of salinity is dependent on the concentration of the nutrient solution, water quality, particle size and porosity of the medium, as well as on the temperature and humidity of the environment. This process is especially intense in summer, when the temperature reaches 30 35 0 C. The inevitable intense ventilation in greenhouses further accelerates evaporation and salt build up on the surface. Salts accumulated on the surface cause rupture of root necks of some plants.

In certain conditions, salts precipitated on the surface of old media are sometimes utilized by the plants, which may cause disorders in their metabolism. In high salinity media the plant tissues are highly saturated by calcium on expense of other cations. Alijev, E.A. (1977) in published results from his research showed, that cucumbers grown on salinated **media had excessive content of calcium in their leaves which resulted in a S premature aging of the plants. Moreover, as a result of the known 15 antagonism between the ions of calcium, magnesium and potassium, the uptake of potassium and magnesium is considerably suppressed.

In the past the salinity problem was solved by flushing of the medium with *:*water, daily disinfecting by formaldehyde and consecutive washing with water or treatment with strong oxidizing agents after several years of 20 usage.

Water soluble salts can be removed by long lasting flushing with water.

Flushing with water slightly acidified with nitric acid will remove nitrates and salts of potassium, magnesium and sodium. Phosphates of calcium, iron and aluminum cannot be satisfactorily removed.

Some simple methods to reduce salinity have been used recently. One of them is dilution of the nutrient solution 2-3 weeks before the removal of the plants. This forces the plants to utilize some of the salts accumulated in the medium.

For removal of sediments from equipment, mechanical and chemical means or their combinations are used. The most common chemical substances are diluted nitric or hypochlorous acids. The system is flushed after being disassembled. The cleaning by diluted acids causes corrosion and premature aging of plastic materials of piping and pumps.

A popular way of the removal of salinity build up from hydroponic media is by diluted hypochlorous acid or its sodium, potassium or calcium salts or alternatively by hydroxides, prevailingly potassium hydroxide. Part of this regeneration is a consecutive lengthy flushing with water and then by diluted phosphoric acid. The disadvantage of this salinity removal is not only its labor intensity, but the fact, that the build up will continue once the operation of the system resumes.

0 Recently various water additives have been used to solve the salinity problem. The additives are capable of reducing or eliminating salinity build up, or continuously removing existing caking from the system by binding the problem cations into water soluble complex compounds and preventing them from creating solid sediments or caking. Similar 15 principles and substances are used for the prevention of salts build up on heating elements of washing machines and water heating systems.

The principal constituent of these additives are some water soluble chelating agents.

If these additives are used in a system which is out of operation, a higher 20 concentration of the chelating agent can be used which is associated with a higher efficiency of salinity removal.

If, however they are used for salinity prevention in an operating system, they have to be added into applied water in a plant growing cycle. In this case the concentration of the additives is limited by the concentration of the sodium cation, which is always one of the principal constituents. The concentration of sodium cation in nutrient solutions is limited or for some sensitive plants completely disallowed (MASON,J: Commercial Hydroponics, Kangaroo Press, Australia 1998).

The process of aging of hydroponic media is accelerated by the increasing amount of decomposing plant and root residues and excrements which are accumulated in the medium as well as in the nutrient solution. These products of decomposition are toxic and have a negative impact on plant development. Most of the toxic products are generated by the decomposition of root residues, with a very slow mineralization process. These particularly inhibit the development of young plants. Treatment of the media by strong oxidizing agents, alkalis and acids, eliminates the negative impact of root residues. The oxidation regeneration of hydroponic media is carried out by hypochlorous acid with the concentration of active chlorine of 1.5 2.0 g/l. Oxidation by hypochlorites, especially sodium hypochlorite is used as well.

We have now found, that most of the disadvantages of the known methods and agents can be effectively overcome by an agent for regeneration of hydroponic media, inhibition of caking and removal of build ups in water systems used for irrigation and/or plant nutrition in soilless hydroponic growing of plants, as well as in fertigation, in which o the agent is used for prevention or correction, and the agent comprises 15 complexing and oxidizing components, and the components are contained in one or more independent liquid concentrates in the form of water solutions, and for the agent according to the invention it is typical, that as active complexing components it comprises chain linearly condensed phosphates, the structure of which can be expressed by a chemical formula: (M)mH(n+ 2 )-mPnO 3 n+l where M is potassium and/or ammonium (NH 4 and/or hydrogen cation n>2 m n+2 and/or it comprises cyclic condensed phosphates, so called metaphosphates (PnOn)n", and said agent comprises between 3.5 wt and 37.5 wt of phosphorus (as P) and between 0 wt and 35 wt of potassium (as and the concentration of sodium cation in the undiluted agent is always less than 3.0 wt and the oxidizing component comprises peroxoacetic acid and/or hydrogen peroxide (H 2 0 2

O

II

CH

3 -C-O-OH

(I)

Complexing phosphorus containing component and oxidizing component of said agent are present as one water solution, or more separate water 10 solutions. A suitable source of prevailingly linear condensed chain phosphates can be so called superphosphoric acid. This can be prepared by a thermal dehydration of orthophosphoric acid or by a reaction of orthophosphoric acid with diphosphorus pentaoxide so as to obtain more than 75 wt of diphosphorus pentaoxide in the final product. By 15 increasing the concentration of phosphoric acid the condensed form of phosphorus is increased and at the same time the distribution of polyphosphoric acids is shifted towards acids with higher content of phosphorus in the molecule.

The structure of chain linearly condensed phosphoric acids can be expressed as follows: H(n+ 2 )PnO(3n+l) O 0 0 II II II II I OH OH OH Blends of condensed ammonium and/or potassium phosphates manufactured by neutralization of thermal and/or purified wet process superphosphoric acid by a suitable alkali e.g. potassium hydroxide or one of potassium carbonates, ammonia or aqueous ammonia, can be alternatively used for the agent according to the invention.

The agent according to the invention can be based on condensed potassium phosphates with either linear chains polyphosphates, or cyclic chains metaphosphates.

Suitable sources of linear polyphosphates could be high polyphosphate type ammonium or potassium polyphosphates 10-34-0, 11-37-0, 12- 40-0, 0-27-30 and others), or tripolyphosphates such as pentapotassium tripolyphosphate or potassium diphosphates, such as tetrapotassium diphosphate.

Both of the mentioned types have a relatively good water solubility (according to published data Kobayashi, E.:J.Chem. Soc. Japan, 83, 132, 1962 66 wt at 0°C for diphosphates and about 65 wt at 25 0

C

S* for triphosphates), which gives a high concentration of the final agent whilst retaining its solution form.

Suitable sources of cyclic polyphosphates are potassium hexametaphosphate or some of the water soluble potassium metaphosphate glasses.

According to the conditions of thermal dehydration as well as partial 20 hydrolysis of condensed phosphates there will always be some monophosphate anions present in said agent. Technical grades of polyphosphates will bring a low concentration of sodium cation into the product.

A great advantage of said agent is that used complexing substances polyphosphoric acids or condensed potassium or ammonium phosphates as complexing substances are sources of fully acceptable plant nutrients phosphorus or phosphorus and potassium, or phosphorus and nitrogen.

The content of these nutrients has to be accounted for in the final recipes of the applied nutrient solutions.

Especially in hydroponic applications it is advantageous that incorporation of said agent causes only minimal or no change in the electric conductivity of the nutrient solutions.

Peroxoacetic acid and/or hydrogen peroxide, which are the oxidizing components of the agent according to the solution are typical of having a high and rapid sterilizing efficiency and have bactericidal effect even at very low concentrations. They also have fungicidal and anti-epidemic effects. Another advantage of these oxidizing agents is that they decompose in the process resulting in water or water and weak acetic acid, which are substances, that are completely harmless to grown plants, personnel, equipment, animals and the environment in general.

It may be advantageous to use a blended oxidizing component containing for instance 30 to 36 wt of peroxoacetic acid, 5 to 12 wt of hydrogen peroxide and up to 1 wt of sulphuric acid.

S" Even if the agent according to the invention can be manufactured as one Ill* :.'":solution, to ensure a long term efficiency and a long shelf life it is more °°°viable to use a form of two or more liquid concentrates (concentrates of 15 complexing phosphate substances and concentrates of oxidizing additives). These can be applied either independently or can be blended prior to their application into the system.

Examples.

The invention is now illustrated but is not limited to the following examples, in which all percentages are expressed on a weight basis.

Example 1 Removal of build ups from piping for hydroponic growing of vegetables as well as regeneration of the medium rockwool, was implemented by adding 41.6 g of polyphosphoric, so called superphosphoric acid in each 1000 liters of nutrient solution applied in the system. The superphosphoric acid contained 34.9 of phosphorus. According to the results of chromatographic analysis it was fount that the used acid contained 17 of phosphorus as orthophosphate and the highest condensed phosphate identified on the chromatogram was n=6 The polyphosphoric acid contained about 38 of total phosphorus as diphosphates nearly 24 of phosphorus as triphosphates and about 13 of phosphorus as tetraphosphate Higher linearly condensed phosphates represented 8 of the total phosphorus added in the system.

At the level of 43.6 mg of total applied phosphorus (as P) in one liter of nutrient solution, after applying the superphosphoric acid it was necessary to reduce by one third the amount of the original phosphorus source (MKP) and consecutively to compensate for reduced potassium by an addition of potassium sulfate. In the process of applying superphosphoric acid it was possible to reduce continuously the application of calcium component (calcium nitrate), since the created calcium polyphosphate complexes rendered the previously insoluble forms of calcium into a plant accessible form.

Example 2.

During regeneration of a hydroponic medium for growing of cucumbers 20 apart from using polyphosphoric acid as in example 1, an oxidizing additive was continuously added.

The oxidizing additive comprised: 33.1 of peroxoacetic acid, C 2

H

4 0 3 9.7 of hydrogen peroxide, H 2 0 2 up to 1% of sulphuric acid, H 2

SO

4 The oxidizing additive was dosed into the blend of nutrient solution and the complexing phosphorus additive in an amount of 0.03 to 0.05 liter per 1000 liters of nutrient solution. This was sufficient to achieve oxidation of root residues and plants excrements, removal of harmful micro-flora and regeneration of the original properties of the medium.

Example 3.

Regeneration of a medium removal of mostly calcium, iron and partly aluminum caking was done by an agent according to the invention which comprised: 12,4 of total phosphorus (as P) 26.2 of total potassium (as K) All of the phosphorus was present in the form of a linearly condensed o *phosphate as tripolyphosphate (P 3

O

1 0 o) 3 The agent did not comprise Ssodium cation. The agent had a character of a solution of a viscous e syrupy consistency. On average 80.6 g of the agent was added in 1000 I .of nutrient solution. This added 10 mg of P and 21.1 mg of K into each 15 liter of the nutrient solution. Since the agent comprised plant nutrients fully acceptable by the plants (carnations), it was possible to reduce doses of phosphorus and potassium through normally used salts (MKP, potassium nitrate and potassium sulphate).

Example 4.

An agent according to the invention was used for regeneration of a medium for growing of vegetables and using drippers. The agent was hexamethaphosphate based, had a character of a water colloid solution and comprised 11.8 of phosphorus (as P) and 14.9 of potassium (as Most of the phosphorus was present in the form of cyclic condensed phosphates. The agent was used in amounts of 75 to 90 g per 1000 liters of nutrient solution. The amounts of phosphorus and potassium were accounted for in the recipe of the nutrient solution.

Example 1000 kg of the phosphate additive for regeneration of hydroponic media was manufactured in a mixing tank using the following procedure: 401.7 kg of potassium hydroxide (KOH) was dissolved in 193.5 kg of water, after which 404.8 kg of polyphosphoric acid was added. The polyphosphoric acid contained 36.7 of phosphorus (as P) and was added slowly whilst the content of the tank was stirred and cooled. The final product the agent according to the invention comprised 14.8 of phosphorus (as P) and 28.0 of potassium as K. The additive had a neutral pH and an appearance of a viscous colloid solution of a syrupy consistency.

*t 2

Claims (3)

1. An agent for regeneration of hydroponic media, inhibition of caking and removal of build ups in water systems used for irrigation and/or plant nutrition in soilless hydroponic growing of plants, as well as in fertigation, in which the agent is used for prevention or correction, and the agent comprises complexing and oxidizing components, and the components are contained in one or more independent liquid concentrates in the form of water solutions, and for the agent according to the invention it is typical, that as active complexing components it comprises chain, linearly condensed phosphates, the structure of which can be expressed by a chemical formula: p (M)mH(n+2)-mPnO3n+l where M is potassium and/or ammonium (NH 4 and/or hydrogen (H cation n 2 m n+2 and/or it comprises cyclic condensed phosphates, so called metaphosphates (Pn03n) and said agent comprises between 3.5 wt and 37.5 wt of phosphorus (as P) and between 0 wt and 35 wt of potassium (as and the concentration of sodium cation in undiluted said agent is always less than 3.0 wt and the oxidizing component comprises peroxoacetic acid and/or hydrogen peroxide (H 2 0 2 O II CH 3 C-O-OH (I) 12

2. An Agent according to claim 1 wherein the source of complexing substances comprises polyphosphoric, so called superphosphoric acid and/or potassium and/or ammonium salts thereof. 1. An agent according to claim I wherein the source of complexing substances comprises potassium triphosphates (P

3 O 10 y 5 and/or potassium diphosphates (P 2 04 4 0s*@ 0@ 0S S S 0 S S OSSS SS S S 055 *S 55 S *SSS S S S. S 5* 5* 0 55 S S .55. 0056 0050 0555 S S 555655 S