Abstract:
In a method for fumigating agricultural land which includes the release of cyanogen into the ground, the cyanogen is released at a depth from 10 cm to 50 cm below the ground surface, and cyanogen is present gaseous form under the release conditions, and the cyanogen is dissolved in water before the release and is released into the ground as an aqueous cyanogen solution.

Description:
BACKGROUND AND SUMMARY 
       [0001]    The invention relates to a method and device for fumigating agricultural land or other land areas. 
         [0002]    Such a method for treating farmland or agricultural areas comprises the release of cyanogen into the soil, wherein the cyanogen is released into the ground at a depth of 10 cm to 50 cm, that is to say the cyanogen is released into the ground through one or more apertures in one or more lines, wherein such one or more apertures is/are located at said depth in the ground. 
         [0003]    The term “release condition” is understood to refer particularly to a pressure of 1 bar of the prevailing atmospheric or ambient pressure, and the respective ambient temperature. 
         [0004]    The treatment of agricultural land with gas (fumigation) comprising biocidal substances such as cyanogen, phosphine, methyl bromide or carbonyl sulphide is generally known, and is used particularly for disinfecting and combating soil-borne pests such as nematodes, harmful fungi, bacteria or undesirable plant seeds. Currently during ground fumigation, cyanogen is introduced into the ground to a depth of 20 to 30 cm via a modified plough, wherein the gas is introduced directly into the furrow and the furrow is covered with soil immediately afterwards. This method is also called “shank injection”. The ground is sealed off with a film as soon as the cyanogen has been applied. 
         [0005]    This release of gaseous cyanogen into the soil may not be satisfactory in warmer climates, one of the main reasons being that cyanogen does not remain in the ground long enough. This leads to more cyanogen being needed to control the pests of concern. If pure cyanogen is injected into the ground as a liquid gas, the low boiling point of the liquid (−21.5° C.) means that some of it evaporates as soon as it leaves the dispensing unit; because under typical release conditions, cyanogen is in the gaseous phase. Accordingly, cyanogen that has been released into the ground evaporates spontaneously and rises toward the surface. This spontaneous evaporation shortens the residence time of the cyanogen in the ground to be sterilized by fumigation, and therewith also the effectiveness of the fumigation. Moreover, a fraction of the cyanogen used escapes into the atmosphere as a result of this evaporation. Even warmer soil temperatures can affect fumigation negatively, because higher temperatures not only hasten the evaporation of the cyanogen, they also reduce the active fumigation time. 
         [0006]    It is desirable to provide a method of the kind described in the introduction with improved performance with regard to the problem complex set forth above. 
         [0007]    Accordingly, according to an aspect of the present invention, it is provided that the cyanogen is dissolved in water before its release, and is introduced into the ground (into a furrow created by a plough, for example) as an aqueous cyanogen solution. 
         [0008]    The cyanogen may be dissolved in water either in the gas-phase or as a liquefied gas. In particular, cyanogen may be dissolved in water particularly advantageously under pressure, particularly under a pressure of 2 bar to 30 bar. If the cyanogen is dissolved in water under elevated pressure more strongly concentrated solutions of cyanogen can be prepared, particularly oversaturated cyanogen solutions. 
         [0009]    The use of cyanogen in an aqueous solution instead of in the gas phase for fumigating areas of agricultural land offers a number of advantages. Firstly, the combustibility of the cyanogen during ground fumigation is reduced and the spontaneous evaporation thereof is suppressed. Secondly, the effectiveness of the cyanogen used for ground fumigation is increased, because the dissolved cyanogen is able to spread over a larger volume and has a longer residence time, thereby prolonging the fumigation period. Consequently, the quantity of cyanogen that has to be used for sterilisation can be reduced. This also has a worker exposure advantage with less cyanogen released into the air meaning it is a safer fumigation process for users. 
         [0010]    In addition, use of a cyanogen solution reduces not only possible cyanogen emissions (release into the atmosphere) during ground fumigation but also the effect of the ground temperature on the fumigation. 
         [0011]    After the cyanogen solution is released, a three-phase system is produced at the release site (in the ground): 
         [0012]    a gas phase, which is formed from the cyanogen evaporating from the liquid, wherein the resulting cyanogen can be used to combat pests, 
         [0013]    a liquid, oversaturated phase, from which cyanogen escapes and can spread widely in the ground, and can also be used to combat pests, and 
         [0014]    a liquid, saturated phase which is formed after outgassing of a part of the cyanogen and has a concentration corresponding to the solubility equilibrium of cyanogen. 
         [0015]    According to one embodiment of the invention, an aqueous, oversaturated cyanogen solution is introduced into the ground. Such an oversaturated solution is particularly characterised by a cyanogen concentration that is greater than the cyanogen concentration given by the Henry&#39;s law constant. In particular, such an oversaturated solution has a concentration of more than 450 ml gas-phase cyanogen per 100 ml water, particularly at 20° C. and 1 bar. 
         [0016]    According to a further embodiment, the oversaturated cyanogen solution has a concentration of more than 8 g/l, more than 9 g/l, more than 10 g/l, more than 11 g/l, more than 12 g/l, more than 13 g/l, more than 14 g/l, more than 15 g/l or more than 20 g/l. The greater the oversaturation concentration of cyanogen in the solution, the stronger the gas phase formed therefrom will be, as described above, and accordingly the more effectively the ground fumigation will be performed. 
         [0017]    According to a further embodiment of the invention, the cyanogen is dissolved in water under a pressure from 1 bar to 30 bar. 
         [0018]    According to a further embodiment of the invention, the cyanogen is dissolved in water by adding cyanogen to a defined flow of water. The advantage of this embodiment is that the cyanogen and the water are thoroughly mixed very quickly. A further advantage is that it offers the capability of providing or producing cyanogen solution continuously, at the release site for example. 
         [0019]    According to a further embodiment, the cyanogen is introduced into the ground using a plough. One advantage of this embodiment is that the desired release depth can be reached with the plough that is used. A further advantage is that the soil to be fumigated is loosened by the plough, and this loosening results in improved propagation of the cyanogen solution and that of the cyanogen that escapes from the solution. 
         [0020]    Such a plough is preferably equipped with gas or liquid delivery system, wherein some or all of the ploughshares on the plough may comprise one or more lines, and wherein the lines are designed to deliver gases or liquids to the tip of the ploughshare, for example. The lines are furnished with apertures through which the aqueous cyanogen solution is or can be released into the soil, and such apertures are located at the intended depth in the soil when the agent is released. 
         [0021]    According to an embodiment of the invention, the ground is covered with a barrier film after the cyanogen solution has been released into the ground. 
         [0022]    The method according to the invention is particularly suitable for use in fumigating geographically challenging farmland, that is to say areas with steep slopes, hills or depressions. Since the cyanogen solution is introduced into the ground and not deposited on the surface, as in other methods, the cyanogen solution remains in place at the release site and is not displaced from its intended release site by the force of gravity. 
         [0023]    According to another aspect of the invention, a device for fumigating areas of agricultural land is provided that has a mixer designed to mix cyanogen and water in a pressure range from 1 bar to 30 bar to form an aqueous cyanogen solution, a first tank that is designed to store and supply cyanogen particularly in a pressure range from 1 bar to 200 bar, the first tank being connected to the mixer so ha cyanogen can be delivered to the mixer from the first tank, and a water supply connected with the mixer, which is designed to store and/or supply said water to said mixer, and a delivery means connected with the mixer, which is designed to release the aqueous cyanogen solution that is produced in the mixer into the ground, preferably at depth from 10 cm to 50 cm below the surface. 
         [0024]    In this context, a connection between two components (for example the tanks, the mixer or the delivery means) denotes a connection in which a flow medium is transported, via which said cyanogen, water or the solution produced therefrom is transportable. 
         [0025]    The term “water supply” shall cover any kind of provision of water, for example by public utilities, a pipe system, a tank, a vessel or any other source. 
         [0026]    According to an embodiment of the invention, the water supply comprises a second tank. Preferably, the second tank is connected to a third tank, the third tank being designed to store and supply a gas or gas mixture, particularly nitrogen (under a pressure from 2 bar to 200 bar for example). In this case, the pressurized gas or gas mixture in the third tank may be used to force or propel the water out of the second tank and into the mixer. 
         [0027]    According to a further embodiment of the invention, the delivery means is in the form of a plough that comprises one or more lines that are fed from the mixer, and each of which has at least one aperture for discharging the cyanogen solution. Lines of such kind with apertures may be provided on ploughshares of the plough, for example. 
         [0028]    One advantage of the device according to the invention is that it offers the capability of continuously producing fresh cyanogen solution with the device, and of introducing it into the ground immediately after it has been prepared. This enables a more effective concentration of cyanogen, because cyanogen in water decomposes over time, initially forming oxamide and subsequently ammonia and carbon dioxide. A more effective cyanogen concentration not only enables more efficient fumigation, but it also means that the quantity of cyanogens required for fumigation can be reduced. 
         [0029]    According to another embodiment of the invention cyanogen is dissolved in water and the resulting aqueous cyanogen solution is released into the ground via a drip tape. The term “drip tape” shall in particular mean tapes, tubes, hoses and dripperlines used in drip irrigation. The drip tape is provided with a large number of outlets, drippers or emitters. Water or any other fluid flows through the drip tape and exits the drip tape through the outlets/drippers. 
         [0030]    The aqueous cyanogen solution is distributed to one or more drip tapes which are either placed onto the ground or, preferably, are placed sub-surface, for example at a depth from 10 cm to 30 cm below the ground surface. The drip tape is preferably located at or close to the final location of the plant roots with the soil fumigation completed pre-planting. 
         [0031]    The water flow rate and the cyanogen volumes are determined by the area to be treated (treatment area), the soil type, the number of drip tapes, the length of the drip tapes and the drip rate, i.e. the volume of aqueous cyanogen solution per time and per length of drip tape. Furthermore, the application time (irrigation time) depends on the water flow rate and the treatment area. 
         [0032]    The ground is covered with a barrier film while the aqueous solution is applied and breaks down in the soil (the soil fumigation process). The barrier film enhances both efficancy as well as worker and bystander safety. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0033]    Further details and advantages of the invention will be explained in the following descriptions of an embodiment thereof, with reference to the drawings. 
           [0034]    In the drawing: 
           [0035]      FIG. 1  shows a device for carrying out the method according to the invention, 
           [0036]      FIG. 2  shows an alternative device according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0037]    Unlike conventional methods, in the method according to the invention as shown in  FIG. 1 , before it is introduced into the ground the cyanogen  21  is dissolved in water  22 , and this aqueous cyanogen solution  23  is then released into the ground, particularly at a depth from 10 cm to 50 cm below the surface. There, the cyanogen  21  is desorbed or is outgassed from solution  23  and rises slowly towards the surface, sterilizing the soil in the process. In order to produce aqueous cyanogen solution  23 , cyanogen  21  and water  22  are mixed in a mixer  13 , wherein the mixture  23  is created by adding gas-phase cyanogen  21  to a defined water flow  22 . In mixer  13 , the cyanogen  21  is preferably dissolved under elevated pressure, an increase in pressure resulting in a stronger concentration of cyanogen in solution  23 . From mixer  13 , the oversaturated cyanogen solution  23  obtained in this way is introduced into the ground via a plough  14 , and the ground is covered with a barrier film. 
         [0038]    The method according to the invention may be carried out for example using a device  100  as represented in  FIG. 1 . Such a device  100  comprises a first tank  11  (also referred to as the cyanogen tank), which is designed to store and supply cyanogen  21  under a pressure particularly from 1 bar to 50 bar. A mixer  13  or mixing chamber  13  is arranged downstream from cyanogen tank  11 , wherein cyanogen tank  11  and mixer  13  are connected to one another via a cyanogen feed line  31 . Cyanogen line  31  comprises a throttle  16  that is designed to relieve the pressurized cyanogen  21 , a diaphragm  17  or mass-controlled regulator for measuring flowrate, and a valve  18 . 
         [0039]    Device  100  further comprises a second tank  12  (also referred to as the water tank), which is connected to mixer  13  via a water feed line  32 , wherein water line  32  also comprises diaphragm  17  or other mass-controlled regulator for measuring flowrate. Water tank  12  is additionally connected to a third tank  15  (also referred to as the nitrogen tank) via a nitrogen feed line  34  wherein nitrogen tank  15  is designed to store and supply nitrogen  24  under a pressure particularly from 2 bar to 200 bar and wherein nitrogen feed line comprises a throttle  16  and a valve  18 . A plough  14  is also provided downstream from mixer  13 , and is connected to mixer  13  via a cyanogen solution line  33 , which is fitted with a valve  18  for metered dispensing of cyanogen solution  23 . Plough  14  is equipped with one or more lines  140 , each of which has an aperture O, through which the cyanogen solution  23  may be discharged into the ground at a predefined depth. Lines  140  may be provided on assigned ploughshares of plough  14 , for example. 
         [0040]    When the method according to the invention is carried out as represented in the embodiment of  FIG. 1 , pressurized cyanogen  21  is forwarded to cyanogens feed line  31  through valve  18 , depressurized to a definable pressure via throttle  16 , and passed to mixer  13 . There, the cyanogen  21  is preferably added to a defined water flow  22 . For this purpose, water  22  is displaced out of water tank  12  and into mixer  13  with the aid of the compressed nitrogen  24  exiting nitrogen tank  15 , wherein the compressed nitrogen  24  forces the water  22  out of water tank  12  and into mixer  13 . The cyanogen solution  23  that is created in mixer  13  is then transported to plough  14  via cyanogen solution line  33  and released into the ground through apertures O in the lines  140 . 
         [0041]      FIG. 2  shows an alternative embodiment of the invention. Cyanogen is stored in a cyanogen tank  11  under a pressure particularly from 1 bar to 50 bar. A static mixer  13  is arranged downstream from cyanogen tank  11 , wherein cyanogen tank  11  and static mixer  13  are connected to one another via a cyanogen feed line  31 . 
         [0042]    Static mixer  13  is further connected to a water supply  222  via a water feed line  32 . One or more drip tapes  214  are also provided downstream from static mixer  13 , and are connected to mixer  13  via a cyanogen solution line  33 . The drip tapes  214  are placed into the ground at a depth between 10 cm and 20 cm below the ground surface. 
         [0043]    When the method according to the invention is carried out as represented in the embodiment of  FIG. 2 , pressurized cyanogen  21  is forwarded to cyanogen feed line  31  and passed to static mixer  13 . There, the cyanogen  21  is added to and thoroughly mixed with a defined water flow  222 . The cyanogen solution that is created in the static mixer  13  is then transported to a number of drip tapes  214  via cyanogen solution line  33  and released into the ground through apertures in the drip tapes  214 . 
         [0000]    
       
         
               
             
               
               
             
           
               
                   
               
               
                 List of reference signs 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 11 
                 Cyanogen tank 
               
               
                 12 
                 Water tank 
               
               
                 13 
                 Mixer 
               
               
                 14 
                 Plough with gas feed line 
               
               
                 15 
                 Nitrogen tank 
               
               
                 16 
                 Throttle 
               
               
                 17 
                 Diaphragm 
               
               
                 21 
                 Cyanogen 
               
               
                 22 
                 Water 
               
               
                 23 
                 Cyanogen solution 
               
               
                 24 
                 Nitrogen 
               
               
                 31 
                 Cyanogen feed line 
               
               
                 32 
                 Water feed line 
               
               
                 33 
                 Cyanogen solution line 
               
               
                 34 
                 Nitrogen line 
               
               
                 100 
                 Device 
               
               
                 140 
                 Lines 
               
               
                 214 
                 Drip tape 
               
               
                 222 
                 Water supply 
               
               
                 O 
                 Apertures