Plant husbandry – Water culture – apparatus or method – Nutrient recirculation system
Reexamination Certificate
1999-10-27
2001-11-13
Jordan, Charles T. (Department: 3644)
Plant husbandry
Water culture, apparatus or method
Nutrient recirculation system
Reexamination Certificate
active
06314676
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to hydroponic plant culture systems in which plants are cultivated in the absence of soil and with their roots located in a flowing aqueous medium containing the plant nutrients.
BACKGROUND OF THE INVENTION
Hydroponic cultivation has several advantages over traditional soil cultivation. In particular, the risk from persistent soil-borne diseases is minimised, there is no damage as a result of repetitive cultivation in the same area and the cultivation crop cycle is shorter. Accordingly, hydroponic cultivation has been expanding rapidly over recent years. Nearly all salad crops commercially grown in the UK are produced in glasshouses by a hydroponic system.
There are two systems for the hydroponic cultivation of plants. Typically plants are grown on a large amount of substrate, such as slabs or blocks of mineral fibre. The slabs or blocks are drip fed intermittently with a nutrient solution. The particular feeding programme depends on conditions affecting rates of nutrient utilisation and water uptake.
Alternatively, the plants are grown by a method known as nutrient film technique (NFT) wherein plants are taken from the propagation block in which they are supplied, and suspended so that their roots are in contact with fast flowing nutrient solution.
For economic use of nutrients, and because of regulatory factors affecting the disposal of nutrient-rich water, the water carrying the nutrients needs to be recycled. This may be carried out continuously or, for instance, by collecting the liquid medium in batches, for instance, one thousand liter batches, and then processing the batches for re-use. Since about 70 percent of the inflowing liquid is retained by the plants, or lost by evaporation and respiration, reprocessing the outflowing liquid effectively involves dilution and re-adjustment of nutrient levels.
Although the hydroponic nutrient solutions contain no organic source of carbon when applied to the plants, the outflowing liquid accumulates organic exudates from the plant roots and also possibly from algae that grow on the well lit surfaces of the growth blocks. As a result, carbon-containing nutrients build up on which plant-pathogenic fungi can grow. Accordingly, a major problem for those operating a recycling hydroponic system is the control of fungal pathogens, and particularly their spores, which tend to accumulate in the liquid and hence constantly re-infect the plants.
The above mentioned problem is currently being tackled by attempting to sterilise the nutrient liquid before it is recycled. Sterilisation methods include pasteurisation, hollow-fibre ultrafiltration, UV-irradiation and chemical treatments using, for instance, ozone or peracetic acid. However, such methods are expensive and they also eliminate a potentially beneficial group of bacteria which may help to control fungal pathogens.
STATEMENTS OF INVENTION
The present invention uses microorganisms capable of suppressing or controlling the growth of pathogenic fungi to suppress or control such growth in hydroponic nutrient solution. More particularly, the present invention provides a method of hydroponic cultivation of plants, the method comprising feeding a nutrient liquid to at least the roots, or parts thereof, of said plants and passing said nutrient liquid through a fibrous filter unit containing one or more cultures of microorganisms, said microorganisms being capable of suppressing or controlling the growth or germination of pathogenic fungi.
The present invention also provides a method of treating nutrient liquid in a hydroponic plant cultivation system, the method comprising passing the liquid through a filter medium having located thereon microorganisms capable of suppressing the growth or germination of pathogenic fungi in the system.
The present invention further provides apparatus for treating nutrient liquid in a hydroponic plant cultivation system, the apparatus including a fibrous filter unit containing one or more cultures of microorganisms, at least one of said cultures being capable of suppressing or controlling the growth or generation of pathogenic fungi.
Microrganisms used in the present invention may also have a bactericidal effect thereby reducing or eliminating harmful bacteria.
The microorganisms are typically bacteria and/or non-pathogenic fungi which have the ability to suppress fungal pathogens. The particular mechanism or mechanisms by which suppression takes place may vary from one microorganism to another. For instance, it is believed that a group of bacteria known as the fluorescent pseudomonads (the
Pseudomonas fluorescens
group) are capable of colonising root surfaces of plants to give effective disease control, possibly by outcompeting the fungi for essential iron.
The filter medium may be pre-impregnated with the microorganisms. Such a filter medium may be freeze-dried for storage purposes. Additionally or alternatively, such a filter medium may also be vacuum-packed. The filter medium may, however, initially be free of microorganisms. They may then be introduced into the system by, for instance, introducing them into the nutrient liquid from where at least some will lodge in the filter medium.
The fibrous filter unit may include one or more mineral fibre slabs or blocks. The fibrous material may be any suitable mineral fibre such as rock wool, glass wool or slag wool. The density of the slab or block is preferably between 25 and 180 kg/m
3
, more preferably between 25 and 120 kg/m
3
, and most preferably between 35 and 80 kg/m
3
.
The fibrous material may be provided in granular form, including, for instance, in the form of short, fibrous lengths of perhaps about 1 mm.
The mineral fibre slabs are preferably rock wool slabs of the type which is manufactured by Grodan A/S of Denmark.
In a method of the present invention, there is employed a biological filter impregnated with a microbial population which includes the appropriate fungus-suppressing bacteria and/or fungi which replaces a sterilisation unit in a hydroponic system. The filter will not only serve to remove fungi and fungal spores from the liquid as a result of its filtration capability but will also provide a continuous seeding of the circulating fluid, and hence the growth blocks in which the plants are located or on which they are supported, with the fungus suppressing microorganism.
It should be appreciated that the microorganisms, or mixture of microorganisms, which are employed may be selected for the particular plant to be cultivated.
MORE DETAILED DESCRIPTION OF THE INVENTION
Among the microorganisms which may be used in the present invention are members of the bacterial genera Pseudomonas, Bacillus, Acinetobactor, Lactobacillus, Flavobacterium, Serratia and non-pathogenic Xanthomonas and actinomycetes. Examples of specific species which may be used, either as the role microorganism or as a component of a mixture of microorganisms, are as follows:
Acinetobactor sp.
Bacillus cereus
Bacillus polymyxa
Bacillus pumilus
Bacillus subtilus
Flavobacterium odoratum
Lactobacillus sp.
Pseudomonas aeruginosa
Pseudomonas alcaligenes
Pseudomonas cepacia
Pseudomonas chlororaphis
Pseudomonas fluorescens
Pseudomonas maltophilia (also known as Xanthomonas maltophilia)
Pseudomonas paucimobilis
Pseudomonas putida
Serratia marcescens
Streptomyces lydicus.
Particularly preferable is isolate 3989A of
Pseudomonas fluorescens
, sourced from a tomato crop grown in a closed environment where
P. cryptogea
was visibly suppressed. Its original identification relied on the presence of fluorescence on Kings B medium. A sample of the microorganism was deposited at the International Mycological Institute of Bakeham Lane, Egham, TW20 9TY, UK on Mar. 6, 1998 under accession no IMI 378597.
The microorganism system of use in the method of the present invention should be capable of becoming established in the filter, in particular as a part of a biofilm.
The invention therefore comprises methods in which the suppressant bacteria or fungi are capable of becoming established as a part of thi
Biofil Limited
Darby & Darby
Jordan Charles T.
Palo Francis T.
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