WO2010062185A1

WO2010062185A1 - Apparatus and method for temperature control of a growth medium in a greenhouse and use of same for control of plant-pathogenic organisms

Info

Publication number: WO2010062185A1
Application number: PCT/NO2009/000391
Authority: WO
Inventors: Michèl VERHEUL
Original assignee: Bioforsk
Priority date: 2008-11-17
Filing date: 2009-11-16
Publication date: 2010-06-03
Also published as: NO328068B1; NO20084820A

Abstract

A temperature regulating apparatus (1) for use with growing of plants in greenhouses, wherein the apparatus comprises at least one tubular body (32, 33) which runs through at least a portion of a growth medium (3) and which is arranged to transport a fluid (4) separated from the growth medium (3). Also described is a method for use of the apparatus and a use of same to control a fungal infection in a growth medium.

Description

APPARATUS AND METHOD FOR TEMPERATURE CONTROL OF A GROWTH MEDIUM IN A GREENHOUSE AND USE OF SAME FOR CONTROL OF PLANT- PATHOGENIC ORGANISMS

In the last decades more and more market gardeners have changed to year-round production of cucumber in greenhouses. Approximately 60% of the cucumbers are now produced with additional lighting. The production arrangement requires high air temperature to achieve a high crop. Many market gardeners have seen a triplication of the crop on a yearly basis. For the distribute trades, sales outlet and the consumers this means a constant supply of high quality cucumbers.

Besides light from the additional lighting, the additional lighting also contributes heat. Heat may also be supplied to the air in the greenhouse from other heat sources.

For intensive cultivation of cucumbers and other useful plants in a greenhouse, it is not the size of the lump of earth which is decisive, but the surface area of the active roots. Thus each plant has a relatively small root ball in the growth medium. Nutrition and water is generally supplied in a drip watering system.

Cultivation in a greenhouse takes place in a controlled environment. Plants are normally not adapted to the earth temperature being as high as the air temperature. In a natural environment the earth temperature will generally be below the air temperature in the growing season. This is due to the earth being in the shade, being covered by an insulating plant cover, that the temperature gradient is partly diminishing descending into the ground and that water diffuses up- ward from the groundwater table.

In greenhouses the temperature in the growth medium will be approximately the same as the air temperature. This is due to the growth medium hanging in the air, the volume of the growth being small and there being little or no temperature gradient from the surface of the growth medium and inward in the growth medium. In addition the water temperature in the drip water plant follows the air temperature. The temperature of the water may in some cases exceed the air temperature in those cases where the irradiance of sunlight heats up the pipeline network and the water in it.

There is thus a need to be able to adjust the temperature in the growth medium independently of the air temperature, and particularly to adjust the temperature to a lower level than the air temperature in a greenhouse.

Plant diseases are a known problem in greenhouses. A high air temperature and high humidity gives good growth conditions particularly for fungus. Examples of such known fungal diseases are mildew (Sphaerotheca fusia, Pseudoperonospora cubensis) , grey mold blight (Botrytis cinerea) and black spot {Didymella bryoniae) .

In latter years the greenhouse industry has suffered considerable economic losses due to root neck rot. This is due to the fungus Pythium aphanidermatum. Fungal species of this family attack a range of economically useful plants such as beet, tomato, pepper, chrysanthemum, cotton and grass, and also species within the gourd family such as cucumber, squash, gourd and melon.

Attacks of Pythium spp give generally poor germination and seed plants wither. Attack on established plants develop as root neck rot. It is however not common for Pythium to do serious damage to established plants. P. aphanidermatum does however great damage to established cucumber plants.

P. aphanidermatum exists all over the planet, particularly in hot regions and in greenhouses. It is mesophilic and prefers temperatures between 27 ⁰C and 34 ⁰C. Basically it is to be considered a water fungus as it thrives and grows best in wet earth and water. Pythium is an oomycetes in the order of Per- onosprales. The fungus survives in earth as oospores, hyphae and sporangia. As oospores it can survive for several years under unfavourable conditions. The sporangia produce zoospores. These are the mobile form of the fungus and may swim about somewhat before they form a cyst and the infectious stadium. Modern cultivation methods using cultivation in relatively small and moist growth media with frequent supply of water up to several times an hour create favourable conditions for development and spreading of zoospores. Recirculat- ing nutrient solution, which is a means to reduce emissions from greenhouse plants, has also turned out to be an efficient way of spreading the zoospores. Disinfecting recircu- lating nutrient solutions is energy demanding and has not given satisfactory results (van Os et al. 2004. Investigations on the crop developments and microbial suppressiveness of Pythium aphanidermatum after different disinfection treatments of the circulating nutrient solution. Acta Hort. 644: 563-570) . Insects may also spread the fungus.

Infection with P. aphanidermatum may be fought in traditional ways. Approved fungicides may be fed to the water. Use of preparations having good effect against P. aphanidermatum, like Previcur (Propamocarb) , causes a release ban for sale of cucumber of three weeks. In a cucumber production having a harvesting period of 9 weeks this leads to a considerable crop reduction. Approval of new preparations is getting increasingly difficult. Recently completed testing of new preparations showed moreover that elimination of attacks by P. aphanidermatum exclusively by use of chemical and biological preparations are not satisfactory (Toppe et al 2007. In- creased productivity in greenhouse cucumber by reduced attack of Pythium rot. Bioforsk Report vol. 2, nr 71) . Good cleaning is important. To get rid of P. aphanidermatum in greenhouses it is recommended to remove all growth media and disinfect all surfaces having had contact with infected material. This is an extensive job.

Good air circulation between the plants, and also good drainage and avoiding over watering are also mentioned as preventive actions.

It is also known that P. aphanidermatum is not a problem as long as the temperature is below 20 ⁰C, and also that it becomes very aggressive when the temperature exceeds 25 ⁰C. Modified cultivation technique using reduced air temperature is thus a possible method to reduce the attacks. However a reduced temperature will also result in loss of crops. Insu- lating water piping and growth media and watering using cold water has been tried. (Ringsevjen, 2002. Mat temperature and effect of watering using cold water and insulation of the medium. Veksthusringen. 17.01.02) . This solution has shortlived effect on the mat temperature and also gives unwanted varying mat temperature. The effect on P. aphanidermatum is also unknown. There is in addition literature indicating that choice of growth medium may be significant. An organic substrate may yield biological resistance and be better suited than an inorganic substrate. Substrates having large water retaining capacity such as rock wool may be less favourable than for example perlite (Van der Gaag and Wever. 2005. Conduciveness of different soilless growing media to Pythum root and crown rot of cucumber under near-commercial conditions. European journal of Plant Pathology, 112 : 31-41) .

There is thus a need to arrive at a new method or new cultivation methods for greenhouse herbs, which limit or prevent fungal attacks. The method should be reliable and be applicable without leading to loss of crops. Ideally speaking the method should neither include use of fungicides so that it may be used for growing of organic and ecological produce.

The object of the invention is to remedy or reduce at least one of prior art drawbacks.

The features stated in the description below and in the following claims achieve the object.

The invention relates in a first aspect to a temperature regulating apparatus for use in plant cultivation in greenhouses where the apparatus comprises at least one tubular body running through at least a portion of a growth medium and which is arranged to transport a fluid separated from the growth medium. The tubular body may be placed in contact with the growth medium on the under side of the growth medium or on the topside of the growth medium. The tubular body may further be placed surrounded by growth medium on all sides. The tubular body may have a chiefly straight shape following a lengthy shape of a vessel wherein the growth medium is placed, or the tubular body may alternatively have a wavy shape in the vessel.

The temperature regulating apparatus as described above may consist of one or more tubular bodies placed side by side such as in a standard duct plate for use in a greenhouse.

The temperature regulating apparatus as described above may be provided with a tubular body further allocated a heat- conducting element extending out from the tubular body and being in contact with the growth medium. The heat-conducting element may be of metal and designed to have a large surface in contact with the growth medium. In an alternative embodiment the heat-conducting element extends between two spaced apart positioned tubular bodies.

A temperature regulating apparatus as described above wherein the fluid is water or the fluid is a gas. In an alternative embodiment the fluid may be an aqueous solution containing glycol or another known cooling medium.

A temperature regulating apparatus as described above wherein the temperature regulating apparatus is connected to a con- trol unit, a valve arrangement and at least one temperature sensor. Opening or closing a valve such as a water cock may manually control the temperature regulating apparatus. The water may flow continuously. A person versed in the art will also know that a control device may be provided for automatic regulating of the flow rate and also the flow speed of the fluid by a pump and valve arrangement being controlled via at least one temperature gauge positioned in the growth medium. The temperature of the fluid may also be controlled by the fluid passing a cooling or heating element or alternatively that a cooling or heating element is positioned in a reservoir containing the fluid. The person versed in the art will also know that a temperature regulating apparatus may be split into several zones as the heat being picked up from the growth medium to the fluid will heat the fluid so that it no longer has the desired temperature controlling effect. Corre- spondingly the heat given from the fluid to the growth medium will, in those cases where a heating of the growth medium is desired, such as in a sprouting phase, cool the fluid so that it no longer has the desired temperature controlling effect.

In a second aspect the invention relates to a method for ad- justing the temperature in a growth medium by means of a temperature control apparatus such that the temperature of the growth medium is controlled by means of a temperature control fluid, which is separated from the growth medium by means of a tubular body. The temperature may be adjusted to a desired temperature interval. This temperature interval may be chosen such that the temperature is inhibitive for growth and reproduction of plant-pathogenic organisms. The plant-pathogenic organism may be fungus, particularly P. aphaniderma turn. Growth of P. aphanidermatum is particularly hampered when the temperature is below 25 ⁰C.

In a third aspect the invention relates to employment of a temperature regulating apparatus to fight or control plant- pathogenic fungal infections when growing plants in greenhouses. It has surprisingly been found that a per se known system for water-borne floor heating is very suitable for the purpose .

In the following is described an example of a preferred embodiment which is illustrated in the enclosed drawings, wherein:

Fig. 1 shows a longitudinal section of a temperature regulating apparatus according to the present inven- tion, wherein the apparatus is arranged to be able to achieve temperature control of a growth medium for plants;

Fig. 2a shows a section of figure 1 seen through the line A-A in figure 1;

Fig. 2b shows a cross-sectional view of an alternative embodiment of the temperature regulating apparatus shown in figure 2a;

Fig. 3 is a diagram showing the number of attacked and dead cucumber plants caused by P. aphanidermatum infection at different treatment methods; and

Fig. 4 is a diagram showing crops of cucumber fruit at different treatment methods against P. aphanidermatum infection.

In the figures the reference number 1 indicates a temperature regulating apparatus according to the present invention wherein plants 2 are placed to grow in a growth medium 3.

In figure 1, five plants 2 are placed to grow in an open vessel 3' filled with growth medium 3. The plants 2 are supplied with natural and artificial light (not shown) in a greenhouse (not shown) . The growth medium 3 is supplied with a nutrition solution (not shown) and surplus nutrition solution may be drained off in a recirculation system (not shown) . The growth medium 3 is placed on the temperature regulating apparatus 1 which in a first end portion is in fluid connection, via lines 1' , with a reservoir 31 containing a temperature regulating fluid 4. The temperature regulating fluid 4 in the reservoir 31 may be temperature regulated by means of a temperature regulator (not shown) . The temperature regulating fluid 4 is led out through a second end portion of the tern- perature regulating apparatus 1 and may possibly be led back (not shown) to the reservoir 31.

The temperature regulating apparatus 1 is connected to a control unit 5, which is connected to a temperature sensor 51 positioned in the growth medium 3 via a signal transmission cable 52. The control unit 5 is arranged to be able to control the fluid flow through the temperature regulating apparatus 1 and comprises at least one valve (not shown) . The valve may be controlled manually based on manual reading of the temperature sensor 51, or the valve may be controlled automatically based on a reading of the temperature sensor 51. The control unit 5 may further comprise a pump (not shown) .

Figure 2a shows a cross-section of the temperature regulating apparatus 1 seen through line A-A in figure 1 and shows the temperature regulating apparatus 1 in the shape of a so- called duct plate 3, which in the embodiment shown consists of ten fluid carrying cavities 32.

Figure 2b shows an alternative embodiment of the temperature regulating apparatus 1 shown in figure 2a. In figure 2b the temperature regulating apparatus 1 is formed by means of four mutually spaced pipes 33 surrounded by the growth medium 3. A plate shaped heat-conducting element 11 extending between the pipes 33 and to either side of the outermost pipes 33 is al- located to the surface of the pipes 33. It is to be understood that the heat-conducting element 11 alternatively, or in addition will be able to project out from each of the pipes 33 in any direction. It has surprisingly been found that a per se known system for water-borne floor heating is very suitable for the purpose. The temperature regulating apparatus 1 of figure 2b is positioned in a vessel 3' which on three sides is provided with a heat insulating material 7. The heat insulating material 7 may also be positioned between the plants 2 on the top sur- face of the growth medium.

Small plants of cucumber (cv Rapides, 3 plants per m²) was planted on rock wool (Grodan Master) or perlite (Plant per- lite No. 2, Pull Norway) in the greenhouse section at Bio- forsk West Sasrheim, Norway. In the greenhouse cultivation ditches were built wherein each ditch has a closed system for recirculating nutrition solution.

The nutrition solution was infected with P. aphaniderma turn grown in Petri dishes under optimal growing conditions. After one week samples of the nutrition solution confirming that inoculation with P. aphanidermatum was successful were taken.

The production took place as a light production using a high wire training system. The growing temperature was: daytimes (30 ⁰C), nighttimes (27 ⁰C), airing temperature (32 ⁰C) . The plants illuminated with 20 klux for 20 hours per day. The lighting was turned off when the natural light, measured outdoors, exceeded 300 W/m². The mats were insulated with expanded polystyrene. Under the mats were positioned a standard duct plate in polycarbonate for use in greenhouses, 18 cm wide and 7.5 m long and 1.2 cm thick. Each duct plate con- sisted of 6 ducts, each duct being 1 cm x 2 cm in cross- section inside. Two and two ducts were interconnected in one end of the duct plate. In the other and of the duct plate a first water hose of plastic material led water into one of the ducts and a second hose led the return water away from the duct plate. The plate was thus connected to 4 input hoses and 4 return hoses. The first water hoses were connected to a reservoir of water holding a temperature of 15 - 16 ⁰C. The water flow was controlled by means of a manual valve and the water was running continuously. The temperature was measured using a thermocouple gauge and the data continuously logged. The temperature of the growth medium for the control group was between 23.9 ⁰C and 31.4 ⁰C during the test, while the temperature in temperature controlled growth medium was between 19.4 ⁰C and 23.2 ⁰C.

The plants were watered with standard cucumber nutrition with electrical conductivity of 2.5. Watering frequency was high; three times 100 ml per hour per plant. pH in the nutrition solution was adjusted with phosphoric acid. The Cθ₂~level in the greenhouse was held at 800 ppm.

Visible attacks on plant neck; number of dead plants and amount of crop was recorded. Some plants from each treatment group were sent to Bioforsk Plantehelse, Norway, to get confirmation of infection with P. aphanidermatum. Harvesting of cucumber started 14 days after test start and went on for 4 weeks .

Table 1. Overview of the various test groups. Same tests were done on rock wool and perlite.

Table 2. Overview of temperatures in the test period (⁰C)

The result for attacks of P. aphanidermatum for the various treatment groups are shown in figure 3. The results for amount of crop for the various treatment groups are shown in figure 4.

In the non-infected control group 38% of the plants were infected and 4% were dead at the end of the test. This shows that the infection pressure was high in the greenhouse.

The best result was reached for the treatment group (no. 3), which was not inoculated with P. aphanidermatum and had cooled growth medium throughout the test lasting for 40 days. This group was not attacked and there were no dead plants. This showed that cooling was sufficient to prevent outbreak of P. aphanidermatum in a greenhouse with high infection pressure. Cooling was not sufficient to prevent outbreak of P. aphanidermatum when the nutrition solution was infected (group no 4), but cooling had a positive effect compared with the result for the infected group, which was not cooled (con- trol group, group no. 2) . The positive effect concerned both number of infected plants and number of dead plants. Cooling of the growth medium in the first 10 days after planting (group no. 5) increased the fungal attack. Particularly more plants died in this group compared with the infected control group. Acidizing of the nutrition solution had a certain limiting effect on the fungal attack.

A reduction of the temperature in the growth medium may be believed to have negative effect on the amount of crop, as the optimal growing temperature for cucumber roots is 22-23 ⁰C. The amount of crop for the various treatment groups is shown in figure 4. The results show that any drop in crops due to lower temperature in the growth medium is more than compensated for in that the plants are healthier. Group 3 that was cultivated having cooling throughout the growing season and only exposed to infection from the surroundings from P. aphanidermatum had significantly (p<0.05) the highest crop. Group 4, which also had cooling throughout the growing season came second best, but the amount of crops was not significantly better than for the non-infected control group and the group being supplied with acidized nutrition solution.

There was no difference between the two different growth media in the extent of the fungal attack as shown in table 3, but the amount of crops was largest at growing on perlite.

Table 3. Attacked plants, dead plants and amount of crops of class I fruit at growing on rock wool and perlite. Average of 12 parallels of 5 plants per treatment.

Growth medium Attacked Dead plants Crop plants (%) (%) (kg/m Vweek)

Rock wool 35.1 (a) 7 .2 (a) 1.53 (b)

Perlite 34.9 (a) 8 .7 (a) 1.97 (a) Equal letter behind the numbers show that the treatments are statistically speaking equal.

Claims

P a t e n t c l a i m s

1. A temperature regulating apparatus (1) for use with growing of plants in greenhouses, c h a r a c t e r i s e d i n that the apparatus comprises at least one tubular body (32, 33) which runs through at least a portion of a growth medium (3) and which is arranged to transport a fluid (4) separated from the growth medium ( 3) .

2. A temperature regulating apparatus (1) according to claim 1, c h a r a c t e r i s e d i n that two or more tubular bodies (32) are positioned adjacent to one another.

3. A temperature regulating apparatus (1) according to claim 1, c h a r a c t e r i s e d i n that the at least one tubular body (33) is further allocated a heat conducting element (11) projecting from the tubular body and being in contact with the growth medium

(3) .

4. A temperature regulating apparatus (1) according to claim 3, c h a r a c t e r i s e d i n that the heat conducting element (11) extends between two mutually spaced arranged tubular bodies (33) .

5. A temperature regulating apparatus (1) according to claim 1, c h a r a c t e r i s e d i n that the fluid (4) is water.

6. A temperature regulating apparatus (1) according to claim 1, c h a r a c t e r i s e d i n that the fluid

(4) is a gas.

7. A temperature regulating apparatus (1) according to any preceding claim, c h a r a c t e r i s e d i n that the temperature regulating apparatus (1) is con^¬ nected to a control unit (5), a valve arrangement, and at least one temperature sensor (51) .

8. A method for regulating the temperature in a growth medium (3) , c h a r a c t e r i s e d i n that the temperature of the growth medium (3) is regulated by means of a temperature regulating fluid (4) , which is separated from the growth medium (3) by means of a tubular body (32, 33) .

9. A method according to claim 8, c h a r a c t e r i s e d i n that the temperature is regulated to an inhibiting temperature for a plant-pathogenic organ- ism.

10. Use of a temperature regulating apparatus according to claim 1 to fight or control plant-pathogenic fungal infections at cultivation of plants in greenhouses.

11. Use of a system for water-borne floor heating to fight or control plant-pathogenic fungal infections at cultivation of plants in greenhouses.