METHOD AND DEVICE FOR DETERMINING THE NITROGEN CONTENT IN AMMONIUM NITROGEN CONTAINING MATERIALS

Abstract: Method and device for simple determination of the nitrogen content of ammonium and urea containing materials, such as manure, digested sludge, compost, soil and the like. The method is characterized by introducing into a gas-tightly sealable container (1, 26), provided with a device (3) for measuring the gas pressure within the container, a predetermined sample quantity of said material and separately thereto an excess of an agent capable of oxidizing ammonium and urea nitrogen into nitrogen gas, gas-tightly sealing the container, from the outside of the container bringing the material sample and the oxidizing agent into contact with each other in the container, and reading the pressure rise due to nitrogen gas evolution caused by reaction of the material sample with the oxidizing agent on said gas pressure measuring device (3), which pressure rise is directly related to the amount of ammonium and urea nitrogen in the material sample.

Description: Method and device for determining the nitrogen content in ammonium nitrogen containing materials. The present invention relates to a method and a device for simple and field determination of the content of ammonium nitrogen and urea nitrogen primarily in various natural manures of animal origin and., particularly liquid manure. The method and the device of the invention may, however, also be used for determining the nitrogen content in such materials as digested sludge, compost, topsoil, etc. The price trend for fertilizers in recent years has caused an increasing interest in the utilization of the plant nutrient contents of farmyard manure, and especially nitrogen, phosphorus and potassium. Potassium and phosphorus are bound in the ground, while the nitrogen nitrified by the soil bacteria is soluble and is easily leached. When spreading liquid manure in the autumn most of the nitrogen is likely to disappear and it must therefore be fully compensated for with fertilizers in spring. Although the nitrogen supply to the soil may be dosed relatively exactly, the nitrogen resource of the farmyard manure is lost. If the farmyard manure is spread in late winter or spring a great part of the nitrogen content will, under suitable conditions, be available to the plants. This part is then possibly supplemented with ertilizer. The rate of the nitrogen supply to the soil, is, however, rather critical to the cultured plants. Too * much nitrogen produces bigger and heavier plants having a loose tissue which fall and form so- called laid corn, while too little nitrogen gives a bad crop yield. A basic prerequisite for the utilization of the nitrogen of farmyard manure is therefore to know the nitrogen content thereof. In addition to the fact that the nitrogen content of farmyard manure may vary from farm to farm, it may also vary in time in the same farm due to, for example, dilution with melt water, evaporation or the microbial degradation process in the marfure basin. For a successful result the farmyard manure should therefore be analyzed on each spreading occasion. Such analysis of the manure is today performed to a very limited extent, and in such a case by having manure samples analyzed in a chemical analytical laboratory. Since the sampling must take place some time before the spreading, the sample, on one hand, will have time to be microbially transformed in relation to the contents of the manure basin during the transport thereof to the laboratory, and, on the other hand, the nitrogen content of the manure will have time to change before the spreading occasion. Although reliable methods of analysis are known since a long time, these methods are complicated and may in practice only be performed in a laboratory. ^^T RI ^ O PI In farmyard manure the nitrogen is primarily bonded, on one hand, organically in amino acids and proteins, and, on the other hand, in the form of ammonium (NH. ). It is the ammonium nitrogen that is nitrified by soil bacteria into nitrate, which is the form that is most easily taken up by the plants. In liquid manure ammonium nitrogen is between 50 and 90%, whereas manure having a higher content of dry matter t and solid manure contain 20% of this nitrogen form. Thus, it is the ammonium nitrogen that is of interest in the analysis. A method of analysis that has been suggested recently for a more extensive analysis of the ammonium nitrogen content in liquid manure is based upon an about 50 years old method for the determination of nitrogen in urine described by Tovborg- Jensen, "Untersuchungen ϋber Ammoniakentbindung und Stickstoffverluste bei der Dϋngung mit Jauche", Arkiv fur Pflanzenbau, _3> 1930, page 161-180. In this method the ammonium nitrogen and possibly present urea nitrogen are oxidized into free nitrogen gas by a sodium hypobromite solution. The evoluted gas is then determined volumetrically. The method has several disadvantages. The sodium hypobromite used as oxidizing agent is, in addition to being expensive, very volatile and emits bromine vapour. The liquid also contains lye which is highly caustic. At least the preparation of the oxidizing liquid requires cautiousness and should be performed in a. so-called fume cupboard. Further, the volumetric gas measurement requires the use of a waterfilled reading tube and various cock connections. For the hitherto suggested apparatus it has also been necessary to filter the manure sample in order to remove the solid constituents before the introduction thereof into the reaction vessel. In summary, the above mentioned disadvantages make it seem difficult to develop an apparatus for this method that can be manufactured in series and used fieldwise in the farms. Nor has any such apparatus hitherto been produced. T e object of the invention is to obviate the disadvantages of the known method and apparatus. This Is accomplished by the method and the device indicated in the subsequent claims and which is further explained below. The method of the invention is based upon the same oxidation principle as the above described hypobromite method but differs essentially in two respects, viz. firstly by, Instead of measuring the gas evolution volumetrically, determining the pressure increase generated by the nitrogen gas in a vessel of constant volume, and secondly, by using a considerably safer oxidizing agent than the sodium hypobromite used in the previous method. Due to this method it will be possible to perform a nitrogen analysis on location, the result being directly readable on a pressure gauge, such as a manometer, since the pressure rise is directly related to the content of ammonium and urea nitrogen. The method may be carried out with a very simple apparatus, which with fully acceptable accuracy of measurement may be made very robust and manufactured in series, and may, in contrast to the previously used hypobromite method, readily be carried out by unskilled labour. The novel simplified method and apparatus of the invention thus makes it possible to introduce nitrogen analysis as a standard procedure in farms having liquid manure equipment, permitting sampling and analysis to take place in direct connection to the spreading. This in turn produces excellent prerequisites for a satisfactory utilization of the plant nutrient of the farmyard manure. The oxidizing agent to be used when practising the invention should be an agent which, like the above mentioned sodium hypobromite, only oxidizes the ammonium and urea nitrogen of the manure into gaseous products. The reaction must additionally not run explosively. Finally, the oxidizing agent should, in contrast " to sodium hypobromite, be substantially safe to handle. As examples of suitable oxidizing agents sodium hypochlorite, potassium hypochlorite and calcium hypochlorite may be mentioned. These agents may be used as solids or solutions. From a practical point of view sodium hypochlorite and calcium hypochlorite would be preferred. The former is commerciably available as an about 12% solution, whereas calcium hypochlorite is the main constituent of chlorinated lime, which is commercialized in solid form. As will appear from the following the solid form may be preferred, since the size of the reagent vessel can be reduced. The reaction between calcium hypochlorite and the ammonium nitrogen of the manure may be represented by the following . ' reaction formula 3Ca(OCl) 2 + 4NH^ + + 4OH " — →-3CaCI 2 + 2N 2 + 10H 2 O Since the reaction is carried out in a closed vessel, the quantity of free nitrogen formed can thus be measured as a pressure rise with a manometer (or other pressure meter), graduated in, e.g., kilograms N/m . A measuring apparatus according to the invention comprises a container capable of being gas-tightly sealed and provided with a suitable pressure measuring device, and into which the manure sample and the oxidizing agent can be introduced separately and kept apart until the container has been sealed. The container is designed such that the manure sample and the oxidizing agent can be brought into contact with each other to permit the desired reaction and nitrogen evolution to take place by operation of the container from the outside thereof. The nitrogen content is then measured on the pressure meter, e.g. a spring manometer, which as mentioned above preferably is graduated directly in nitrogen content. A simple and convenient embodiment of the invention thus consists of a can-shaped container having a gas-tightly attachable lid or cover. The lid is provided with a manometer, and in the interior thereof the container carries a smaller container for oxidizing agent, which container can take two positions, viz. a first position where the oxidizing agent can be introduced into the oxidizing agent container and be retained there, and a second position where the oxidizing agent container, e.g. through rotation about an axis, no longer can retain the oxidizing agent but empties it towards the bottom of the container. The operation of the oxidizing agent container from the outside of the reaction vessel, after the lid has been attached, may take place by an operating arm or 0 the like via a lead- through in the vessel wall, but the oxidizing agent container may also be arranged such that it can be brought to said second position simply by tipping or tilting the apparatus. In the latter case It may, for example, be relatively freely journalled on a horizontal axis in the container, such that it in an upper position leans against th inner wall of the vessel and can be tipped to -5 rotate downwards to hang with the opening towards the bottom of the vessel. Optionally a free container may be used as oxidizing agent container, which container is placed in the material sample on the bottom of the vessel or on a suitable step inside the container. Other arrangements accomplishing the same function are, of course, also within the scope of the invention. Optionally means 0 are provided for agitating the reaction mixture as well as suitable means for thermostatting the reaction vessel. For practical use, however, a sufficient accuracy of measurement would be obtained even without such thermostatting. Said optional agitating means may either be separate or combined with the oxidizing agent container, such that stirring is performed by turning the latter in 5 the reaction vessel. With such a device the method of the invention can practically be carried out by introducing a predetermined manure sample into the container, intro¬ ducing an excess of oxidizing agent (in relation to the ammonium and urea nitrogen in the manure sample) into the oxidizing agent container and fastening 0 the lid provided with ' the manometer. The oxidizing agent Is then brought into contact with the manure sample in suitable manner, the reaction mixture is agitated and, when the reaction is completed - which takes about I minute - the result of the analysis is read on the manometer. The method is thus extremely simple to carry out and, even without -5 thermostatting, gives an analysis result which is sufficiently accurate in relation to the accuracy obtained for the very sampling and the accuracy obtained for the subsequent spreading of the farmyard manure. A great advantage of the method of analysis according to the invention, wherein in contrast to the previous method no filtrate is used but a whole manure sample added, is that the nitrogen___ content is obtained related to the sample material including gravel, straw, sawdust and the like which may be contained in the liquid manure. The measuring apparatus of the invention can be made very simple and robust and easy to clean and is therefore excellently suited for use in the field. Further, it is completely safe to use, since the pressure rises operated with are not very great. A suitable pressure increase is, for example, of the order of 1 kp/c . As indicated above the analysis also comprises urea, which is not any disadvantage since the nitrogen in this form is quickly transformed into ammonium nitrogen. In most cases this will have taken place substantially completely already in the liquid manure container. As mentioned above the method and the device of the invention are, of course, not restricted to the determination of the ammonium nitrogen content of liquid manure, but may as well, possibly with some modifications, be applied to liquid manure with a higher content of dry matter and solid manure, compost, topsoil, etc. In the following the method and the device of the invention are further illustrated with respect to some particular embodiments, reference being made to the accompanying drawings, wherein Fig. 1 is a perspective view, with parts broken away, of an embodiment of a measuring device according to the invention, Fig. 2 is a schematic side elevation, partially in section, of the measuring device of Fig. 1 without the lid and with the oxidizing agent container in a first position, Fig. 3 is a corresponding view to Fig. 2 but with the lid attached and the oxidizing agent container in a second position, Fig. 4 is another embodiment of the measuring device according to the invention and Fig. 5 is a perspective view of an embodiment of a manure sampler for use in the invention. The device shown in Fig. 1-3 comprises a box-shaped container or reaction vessel 1, which may be gas-tightly closed with a lid 2. To the lid a manometer, such as a spring manometer 3, is fixed, the measuring aperture of which opens on the inner side of the lid. A splash shield for the manometer measuring aperture is attached to the lid. The lid 2 has downwardly projecting edges 5, which, when the lid is mounted, extend downwards over the top of the container 1 and fixes the lid against lateral displacements. A gasket 6 of an oxidation resistent material, e.g. EPDM, Teflon or the like, is arranged in the lid 2 along the lateral edges thereof. Optionally the gasket 6 may extend over the whole inside of the lid with the exception of the manometer lead-through and the splash shield 4. The lid 2 is clamped to the container 1 by means of, on one hand, two bracket means 7 at either end of one side edge of the lid, which grasp corresponding tap members or supports S fixed to the upper part of the container 1, and, on the other hand, a hook means 9 on the opposite side edge of the lid and arranged to receive the bracket member 10 of a conventional clamp locking device 11. The locking or clamping force can in conventional manner be adjusted by the bracket member 10 being screwably arranged in a horizontal, rotatably journalled axis 12 of the clamp locking device. The manometer 3 is preferably, as is shown in the Figures, attached by screwing in a threaded lead-through 12 of the lid 2 and optionally fixed by a nut 13 to permit easy replacement of the manometer. An internal trough-shaped container 14 for oxidizing agent is disposed within the container 1 and supported on a horizontal axis 15 through mounting braces 16. The axis 15 is rotatably journalled in a gas-tight bushing or lead- through 17 in one sidewall of the container 1 and may be operated by means of an operating arm IS attached to the axis 15 on the outside of the container 1. The gas-tight bushing 17 may, as shown in Fig. 1, consist of an externally threaded cylinder part 1 fixed in the container wall and provided with a central ' bore or . the axis 15. A cap nut 20, screwn on the cylinder part 19, presses a gas-tight, oxidation resistant sealing 21, e.g. one or more Teflon rings, against the axis 15 and the cylinder part 19. The trough or oxidizing agent container 14 may, due to the above described arrangement, be pivoted from first position, or filling position, shown in Fig. 1 and 2, where the trough 10- has its opening facing upwards and preferably rests with one side edge thereof against the adjacent side wall of the container I to prevent oxidizing agent from being spilled into the container 1 during the charging thereof. The size of the trough 1 is adapted such that it can hold an excess of oxidizing agent in relation to the amount of manure sample to be introduced into the container, as will be further explained below. By turning the operating arm IS in counter clockwise direction the trough 14 can be pivoted to a lower position, shown in Fig. 3, where the trough has Its opening facing downwards. Although in Fig. 3 the trough 14 is shown with the opening facing the bottom of the container 1, the trough may be pivoted as far as to the end position shown with broken lines, where the side edge of the trough goes against the container side wall. In order that the projecting portion of the manometer 3 on the inner side of the lid 2 should not prevent the pivoting movement of the trough 14 within the container, the manometer is disposed at a sufficient distance from the trough at one end of the lid. Due to the cooperating locking members 7, 8 of the lid 2 and the container 1, respectively, the lid can not be fixed in an incorrect position preventing the pivoting movement of the trough. For reasons which will appear below, the lower edge of the oxidizing agent container 14 should, in the lower part of the pivoting path shown in -Fig. 3, be relatively close to the bottom. A suitable material for the container is, for example, stainless steel, but other oxidation resistant materials, such as suitable plastic materials, may also be used. As mentioned above an overpressure of about one atmosphere is a suitable overpressure to operate with and does not put any extreme requirements upon the strength of the measuring apparatus. The apparatus may optionally be provided with a safety valve, but the conventionally arranged bursting opening would be sufficient to prevent accidents, if the pressure rise in the apparatus for any reason should become too great during the measurement. To analyse the nitrogen content of, for example, liquid manure one may proceed in the following manner. As mentioned above the sampling should take place in direct connection to the ' spreading of the farmyard manure, the latter being homogenized through agitation. Suitably, a larger sample is taken from the agitated manure basin by means of a bucket or the like. From the bucket a predetermined quantity of manure sample is then taken by means of a special sampler, e.g. designed as the sampler 22 in Fig. 5. The sampler shown therein consists of a cylindric container 23 having a handle 24. The container 23 should be relatively high and thin to provide good accuracy for the sample volume , withdrawn. To sample the sampler is introduced into the bucket with liquid manure (alternatively directly into the manure basin), so that the container 22 is filled to the brim. After the lid 2 has been removed from the measuring apparatus and the oxidizing agent container 14 being in the upper position (Fig. 2), the manure sample is poured Into the container 1. Oxidizing agent, e.g., chlorinated lime, is then filled into the trough 14. The oxidizing agent should be added in excess in relation to the estimated maximum ammonium nitrogen and urea nitrogen amount of the manure sample and may be dosed with a similar sampler as the manure sampler of Fig. 5, or alternatively filled to a suitable marking in the trough 14. Since the nitrogen content varies substantially between various types of liquid manure, various sizes of the fillers for manure sample and oxidizing agent, respectively, are suitably used. For example, liquid manure from swine and cow usually contain about 5-6 kg N/m , poultry manure up to about 40 kg N/m 3 and digested sludge about 0,5-1 kg N/m 3. An excess of oxidizing agent of 15-20% may be suitable. For a reaction vessel volume of about 1,4 liters OMPI S • 3 a suitable sample amount of swine/cow manure is about 200 cm and a corresponding suitable addition of chlorinated lime about 50 cm . This gives an approximate overpressure of about 1 kp/cm in the subsequent reaction. After charging the oxidizing agent the lid is attached and clamped by means of the clamp locking device 11. The operating arm 18 is then brought -in counter clockwise direction (in the direction of the arrow)to the position shown in Fig. 3, whereby all the , oxidizing agent in the trough 14 is emptied into the manure sample on the bottom of the container. Thereafter the operating arm 18 is moved forwards and backwards in the lower position thereof, the inverted trough 14 functioning as an agitator so that the mixture is stirred properly. The splash shield 4 prevents splashes from the mixture from entering into the manometer opening. After about 1 minute the reaction is completed, and the pressure rise obtained is read on the manometer scale 25. The latter is suitably graduated directly in, for example, kilograms N/m , the scale being directly dependent of the size of the manure sample container. It may be convenient to have three parallel scales on the manometer corresponding to three sizes of manure sample fillers, e.g., the following scales of 0-4 kg N/m , 0-10 kg N/m 3 and 0-40 kg N/m 3 . •In the above described manner an analysis of the contents of ammonium nitrogen and urea nitrogen in a manure sample is thus quickly and conveniently carried out. While the measuring apparatus of the invention is particularly suitable for the determination of nitrogen in liquid manure and digested sludge, it may, as mentioned above, also be used for analyzing liquid manure of higher dry matter content and solid manure, compost, top-soil, etc. In Fig. 4 another embodiment of the measuring apparatus of the invention is shown, which is somewhat simpler to manufacture than the measuring apparatus of Fig. 1-3. The container 1 in Fig. 1-3 is here corresponded by a cylindric container 26, and the lid 2 by a lid 27, in the centre of which the manometer 3 is disposed. The lid Is clamped with a number, in the shown case three, of clamp locking devices 11, whose bracket members 10 engage recesses 28 in the edge of the lid. In the same way as In the previous embodiment an oxidation resistant gasket 6 extends at least along the contact edge of the lid 27 with the container 26. Also in this case a splash shield 4 is arranged in front of the measuring opening of the manometer 3. The oxidizing agent container consists of a cylindrical container 29 attached to a horizontal pivot arm 30, which is rotatably journalled In two projections, e.g. tube taps 31 fixed to the inner wall of the container 26. Tne oxidizing agent container 29 is suspended to be capable of occupying a semi-stable upper position (as is shown in the Figure JRH with solid lines), in which the upper part of the container 29 rests against the inner wall of the reaction vessel 26. Since the pivot axle 30 is freely journalled in the tube taps 31 the container 29 can be brought to pivot down to the position shown in dashed lines by merely tilting the. apparatus. Manure analysis is performed essentially in the same way as described above in connection with the embodiment of Fig. 1-3. Thus, a predetermined quantity of the manure sample is introduced into the container 26 with a sampler or filler 22 (Fig. 5), a suitable amount of oxidizing agent (excess) is charged and the lid 27 is clamped. Then the apparatus is tilted so that the oxidizing agent container pivots downwards and the contents thereof are emptied over the manure sample. Optionally the outside of the container 26 may be provided with supports to allow the apparatus to be left in a tilted position. The measuring apparatus is then carefully shaken to mix the contents thereof. In the same way as above a reliable value of analysis for the nitrogen content can be read on the manometer scale 25 after about one minute. As appears from the above the described measuring devices according to the invention are robust, safe to use and may be manufactured at a relatively low cost. An essential advantage is also that they are very simple to clean. The method and the device of the invention are, of course, not restricted to the above described and specifically shown embodiments, but many variations and modifications may be made within the scope of the general inventive concept as it appears from the subsequent claims. For example, it is not necessary for the oxidizing agent container (14, 29) to be journalled in the reaction vessel, but it may be a completely unattached part or alternately a fixed integral part of the container. In the former case it may, e.g., be a container which is placed in the manure sample on the bottom of the reaction vessel, and in the latter case a container -shaped shelf, step or the like fixed to the inner side of the apparatus. In both cases the oxidizing agent is contacted with the manure sample by tilting or inverting the apparatus. While a conventional spring manometer is a suitable pressure gauge, other pressure measuring devices may also be used. As mentioned above means for thermostatting the reaction vessel may optionally be provided. Further, the operating means (18) in Fig. 1 must not necessarily be mechanically connected to the oxidizing agent container, but actuation of the latter may also take place through magnetic action.

Claims: CLAIMS 1. A method of determining the nitrogen content of ammonium and urea containing materials, su.ch as manure, digested sludge, compost, soil and the like, . characterized by introducing into a gas-tightly sealable container (1, 26), provided with a device (3) for measuring the gas pressure within the container, a predetermined sample quantity of said material and separately thereto an excess of an agent capable of oxidizing ammonium and urea nitrogen into nitrogen gas, gas-tightly sealing the container, from the outside of the container bringing the material sample and the oxidizing agent into contact with each other within the container, and reading the pressure rise due to nitrogen gas evolution caused by reaction of the material sample with the oxidizing agent on said gas pressure measuring device (3), which pressure rise is directly related to the amount of ammonium and urea nitrogen of the material sample. 2. The method of claim 1, characterized in that sodium hypochlorite, potassium hypochlorite, calcium . hypochlorite, chlorinated lime or mixtures thereof, preferably chlorinated lime, are used as oxidizing agent. 3. The method of claim 1 or 2, characterized in that the temperature is kept substantially constant during the reaction. 4. A device for determining the nitrogen content of ammonium and urea containing materials, such as manure, digested sludge, compost, soil and the like, characterized in that it comprises a gas-tightly sealable first container (1, 26) having at least one opening for the introduction of a material sample and oxidizing agent, and a pressure measuring device (3) for measuring the pressure in the container, said container comprising at least partially separated or separable spaces for the material sample and oxidizing agent, respectively, arranged to be capable of keeping the two substances separated, but through operation of the sealed container from the outside thereof permit mixing of the substances with each other. 5. The device of claim 4, characterized in that the container (1, 26) comprises a gas-tightly attachable lid (2, 27), to which the pressure measuring device (3) is fixed. 6. ' The device of claim 4 or 5, characterized in that said space for the oxidizing agent is a second container (14, 29) which is rotatably journalled in said first container (1, 26) between a first position, where the oxidizing agent is retained therein, and a second position, where the oxidizing agent is emptied into said first container (1, 26). 7. The device of claim 6, characterized in that the oxidizing agent container (14, 29) is actuable from the outside of said first container (1, 26) through operating means (18) arranged on the outer wall of the container. 8. The device of claim 7, characterized in that said operating means (18) are mechanically connected to the oxidizing agent container (14, 29) through a gas-tight lead-through means (19, 20, 21) in the container wail. 9. The device of any one of claims 4-8, characterized in that it comprises agitating means. 0~. The device of claim 9, characterized in that the oxidizing agent container " (14) also is capable of operating as said agitating means. 11. The device of any one of claims 4-10, characterized in that " the pressure measuring device (3) is a spring manometer. OMPI _

Inventors: ENGLUND CLAES ANDERS, JOHANSSON LARS ERIK GUSTAV
Applicants: ENGLUND CLAES ANDERS, JOHANSSON LARS ERIK GUSTAV
Application year: 1982
Main classification: G01N7
IPC codes: G01N7, G01N31