Method and device for detecting carbon and nitrogen elements in fresh soil

Abstract

The invention discloses a method and device for detecting carbon and nitrogen elements in fresh soil. The method comprises the steps of pipeline air exhaust, water quantification, low-temperature cracking, medium-temperature oxidation, high-temperature combustion and the like. The device comprises a combustion furnace, a heat exchange tube, an electronic condenser, a dehalogenation device, a flow divider, a collector, a reduction furnace, a carbon adsorption column and a TCD detector. The electronic condenser is used for cooling the vaporized atmosphere in the fresh soil, real-time high-precision quantitative analysis is carried out on the water content, and the content of carbon and nitrogen elements in the fresh soil is converted into the content of carbon and nitrogen in the dry soil through the water content of the soil; the contents of carbon or nitrogen in various forms are distinguished by utilizing staged combustion detection for the first time, the contents of main nutrient elements of carbon and nitrogen in the soil can be rapidly and accurately determined in a field edge site, and compared with determination after air drying of a soil sample, the detection time is greatly saved; the determination result of the method can guide field fertilization, provides a scientific basis for agricultural production, and serves modern agricultural development.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soil element detection, and particularly relates to a method and device for detecting carbon and nitrogen elements in fresh soil. BACKGROUND

[0002] With the continuous advancement of agricultural modernization, centralized operation and technological planting gradually become a new trend of agricultural development, and the demand for rapid detection of soil nutrients is increasingly urgent. However, in the conventional process of existing soil carbon and nitrogen element analysis, including sample collection, laboratory air drying, grinding and element analyzer determination, the whole process needs to consume at least ten days, resulting in long analysis period and low efficiency. Therefore, the existing element analyzer cannot meet the demand of on-site rapid detection.

[0003] The soil water content is changed by factors such as rainfall, irrigation and water evaporation, and it is necessary to determine the soil water content synchronously, so as to convert the carbon and nitrogen element content in fresh soil into the carbon and nitrogen element content in dry soil, so as to have practical guiding value for agricultural production.

[0004] The traditional element analyzer is only suitable for the determination of air-dried soil samples, because the chemical adsorbent has limited ability in removing water, and can only remove trace amount of water. If the fresh soil sample is directly determined, the intervention of a large amount of water will cause the chemical adsorbent to fail quickly. The chemical adsorbent (such as magnesium perchlorate) has poor water tolerance, and cannot handle the high water content of fresh soil. In addition, water has absorption characteristics in the infrared spectrum region, which will have a significant interference effect on the detector.

[0005] In addition, soil organic carbon is closely related to life activities, and accurate distinction of it is essential for soil nutrient management, which can provide more accurate data. Especially in calcareous soil, it is necessary to understand the content of inorganic carbon and organic carbon and their contribution to soil nutrients, which must rely on modern analysis technology capable of distinguishing the two kinds of carbon. However, the traditional element analyzer usually adopts a one-time cracking method when processing soil samples, which cannot effectively distinguish inorganic carbon and organic carbon.

[0006] Therefore, a new soil nutrient on-site rapid detection process and its supporting device are needed, which can rapidly and accurately determine the content of carbon and nitrogen main nutrient elements in soil on the spot, the determination results guide field fertilization, provide scientific basis for agricultural production, and serve the development of modern agriculture. SUMMARY

[0007] The present application relates to the technical field of soil element detection, and particularly relates to a method and device for detecting carbon and nitrogen elements in fresh soil.

[0008] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0009] The present application firstly proposes a method for detecting fresh soil carbon and nitrogen elements, comprising the following steps:

[0010] S1, pipeline exhaust air:

[0011] A fresh soil sample (<3g) is placed in a combustion furnace, and oxygen is used at an inlet flow rate of 20-30 mL / min to perform exhaust treatment on the combustion furnace, heat exchange pipe, electronic condenser, dehalogenator, and flow divider. The exhaust gas is discharged from the exhaust port of the flow divider to the pipeline, and the oxygen content in the pipeline is >99%. The exhaust port is closed.

[0012] S2, water quantification process:

[0013] The oxygen inlet is closed, and the heat exchange pipe is closed to make the dehalogenator inoperative. The combustion furnace, electronic condenser, dehalogenator, and flow divider form a circulation loop. The temperature of the combustion furnace is controlled at 105±2℃. The electronic condenser condenses the volatile gas atmosphere, and the gas circulates for 6-8 min. The water content in the circulating gas at the bottom of the combustion furnace is <0.1%. The water mass in the electronic condenser (the water gradually condenses in the liquid reservoir below the electronic condenser, and the water volume is measured by a microliter pipette to convert the condensed water mass) is recorded, and then divided by the soil sample weight to obtain the water content in the soil.

[0014] The soil moisture result can be used to judge the soil moisture condition and to convert the soil carbon and nitrogen results.

[0015] By quantifying the water content in the fresh soil, the directly measured carbon and nitrogen element results are converted into the carbon and nitrogen contents in dry soil. The water content in the fresh soil with a mass of m is a%, and the nitrogen content obtained by TCD testing is k0, which is mg nitrogen / g fresh soil. The nitrogen content in dry soil is converted as follows:

[0016] k1=(k0×m)÷[(1-a%)×m], which is mg nitrogen / g dry soil.

[0017] For example, if the water content in 2g of fresh soil is 20%, and the nitrogen content obtained by subsequent TCD testing according to the present application is 50 mg nitrogen / g fresh soil, the nitrogen content in dry soil is converted as follows:

[0018] (50 mg / g×2g)÷[(1-20%)×2g]=62.5 mg nitrogen / g dry soil.

[0019] The real nitrogen / carbon content in the soil can be tested by accurate quantification of the soil moisture, which avoids the uncertainty of the soil moisture content, resulting in a determination result without agronomic guidance significance.

[0020] S3, low-temperature cracking:

[0021] With oxygen at an inlet flow rate of 50-60 mL / min, open the heat exchange tube, close the straight pipe between the combustion furnace and the electronic condenser, and close the straight pipe between the flow divider and the combustion furnace, open the pipe between the flow divider and the collector, close the oxygen inlet valve, open the carrier gas inlet valve at the bottom of the combustion furnace (to drive the combustion tail gas into the flow divider with carrier gas);

[0022] Open the collector, reduction furnace, carbon adsorption column and TCD detector in turn, and pass carrier gas into one end of the collector, the carrier gas being He or Ar, preferably He, to make the dehalogenator work, rapidly raise the temperature of the combustion furnace to 310°C ± 5°C, react for 5-8 min, detect the nitrogen content in the TCD detector after reduction, desulfurization and carbon adsorption, convert it into the microbial nitrogen content in the soil, then desorb the carbon dioxide in the carbon adsorption column, and detect the carbon dioxide content in the TCD detector, which is converted into the organic carbon content in the soil;

[0023] Under this temperature condition, the microbial nitrogen or other organic carbon in the soil reacts with pure oxygen, and generates N2 and CO2 through catalytic reduction, and the nitrogen content detected by the TCD after adsorption by the carbon adsorption column can be converted into microbial nitrogen, and the carbon content after desorption can be converted into the content of organic carbon. Generally, microbial nitrogen (calculated as nitrogen) is 11-15 mg of nitrogen per kg of soil, and organic carbon is 0.5-7.0% as the criterion. If the organic carbon is insufficient, measures such as applying organic fertilizer and returning straw to the field can be taken to improve the organic matter. In addition to organic pollution, the higher the organic matter, the higher the fertility, such as the black soil in the northeast, which basically contains about 6% of organic matter;

[0024] S4, medium temperature oxidation:

[0025] With oxygen at an inlet flow rate of 80-100 mL / min, open the heat exchange tube, close the straight pipe between the combustion furnace and the electronic condenser, and close the straight pipe between the flow divider and the combustion furnace, open the pipe between the flow divider and the collector, close the oxygen inlet valve, open the carrier gas inlet valve at the bottom of the combustion furnace, open the collector, reduction furnace, carbon adsorption column and TCD detector in turn, and pass carrier gas into one end of the collector, the carrier gas being He or Ar, preferably He, to make the dehalogenator work, rapidly raise the temperature of the combustion furnace to 620°C ± 10°C, react for 5-7 min, detect the nitrogen content in the TCD detector after reduction, desulfurization and carbon adsorption, convert it into the organic nitrogen content in the soil, then desorb the carbon dioxide in the carbon adsorption column, and detect the carbon dioxide content in the TCD detector, which is converted into the elemental carbon content in the soil;

[0026] Under this temperature condition, the organic nitrogen or elemental carbon in the soil reacts with pure oxygen and is catalytically reduced to generate N2 and CO2, and after adsorption by the carbon adsorption column, the nitrogen content detected by the TCD can be converted into the content of organic nitrogen, and after desorption, the carbon content can be converted into the content of elemental carbon. Generally, the content of organic nitrogen (calculated as nitrogen) is 45-60 mg of nitrogen per kg of soil, and the content of elemental carbon is 0.05-1.0% as the determination standard. If the organic nitrogen is insufficient, organic nitrogen fertilizer or nitrogen-fixing bacteria should be supplemented. Generally, the higher the content of elemental carbon, the higher the surface soil porosity, but excessive seepage can also cause the soil to have lower water retention, so when the content of elemental carbon is low, straw can be supplemented and applied with fertilizer before soil turning; when the content of elemental carbon is low, carbon decomposition bacteria or water retention agents should be applied;

[0027] S5, high-temperature combustion:

[0028] An oxygen inlet flow rate of 70-90 mL / min is used, the heat exchange tube is opened, the straight-through tube between the combustion furnace and the electronic condenser is closed, the straight-through tube between the flow divider and the combustion furnace is closed, the tube between the flow divider and the collector is opened, the oxygen inlet valve is closed, the carrier gas inlet valve at the bottom of the combustion furnace is opened, the collector, the reduction furnace, the carbon adsorption column, and the TCD detector are opened in sequence, and a carrier gas is introduced into one end of the collector, the carrier gas being He or Ar, preferably He, so that the dehalogenator is in working condition. The temperature of the combustion furnace is rapidly raised to ≥900℃ (generally, calcium carbonate is the main component of carbonates in the soil, and 930±30℃ can be selected; when the content of barium or strontium in the soil is high, the temperature can be raised to 1350℃ or 1450℃ to reach the decomposition temperature of barium carbonate or strontium carbonate in the soil), the reaction is carried out for 3-5 min, after reduction, desulfurization, and carbon adsorption, the nitrogen content in the TCD detector is detected, which is converted into the content of organic nitrogen in the soil, and then the carbon dioxide in the carbon adsorption column is desorbed, and the carbon dioxide content in the TCD detector is detected, which is converted into the content of carbonates in the soil;

[0029] Under this temperature condition, the inorganic nitrogen and carbonates in the soil react with pure oxygen and are catalytically reduced to generate N2 and CO2, and after adsorption by the carbon adsorption column, the nitrogen content detected by the TCD can be converted into the content of inorganic nitrogen, and after desorption, the carbon content can be converted into the content of carbonates. Generally, the content of inorganic nitrogen (calculated as nitrogen) is 6-9 mg of nitrogen per kg of soil, and the content of carbonates is 0-0.5% as the determination standard. If the inorganic nitrogen is insufficient, nitrogen fertilizer should be applied, and if it exceeds, nitrogen fertilizer can be temporarily not applied, and attention should be paid to environmental problems caused by excessive nitrogen fertilizer. The content of carbonates can reflect the soil texture properties, and when the content exceeds 0.5%, it is easy to be compacted and cannot retain water and fertilizer. The content of carbonates in high-nutrient red soil or black soil is less than 0.5% of the weight percentage of the soil, and when it exceeds 0.5%, agricultural measures such as straw returning can be taken to change the soil structure;

[0030] According to the contents of organic carbon, carbonate, organic nitrogen and inorganic nitrogen, the soil fertility is improved by appropriate agricultural measures such as moisture, fertilizer, organic matter, acid and alkaline, and water and fertilizer retention rate, so as to provide conditions for crop growth and improve crop yield.

[0031] The application also provides a device for detecting fresh soil carbon and nitrogen elements, which is applied to the method.

[0032] The shunt is provided with two outlets, one of which is a waste gas outlet, and the other is connected to the collector. The actual gas amount entering the detection section is controlled by the flow ratio of the two outlets. The shunt controls 50% of the combustion of the gas to be detected to enter the detection section. When the nitrogen content in the soil obtained by the detection section is 15 mg of nitrogen per gram of soil, the actual nitrogen content in the real soil is 15÷50%=30 mg of nitrogen per gram of soil. This is because the soil with high nitrogen content may affect the working load of the reduction furnace and the upper limit of the TCD detection, thereby reducing the working saturation.

[0033] Preferably, the gas outlet of the combustion furnace is connected to the heat exchange pipe and the electronic condenser through a three-way valve, the other end of the heat exchange pipe is connected to the electronic condenser, and the heat exchange pipe is provided with circulating water at 5-30 DEG C for heat transfer wall heat conduction cooling. The obtained circulating water can also be used as a non-direct contact heat exchange medium between the electronic condenser and the dehalogenator to improve the dehalogenation efficiency.

[0034] Preferably, the electronic condenser adopts a three-stage Peltier refrigeration fin combined structure, and the temperatures of the three-stage Peltier refrigeration fins are 10 DEG C, -5 DEG C and -15 DEG C (with an error of not more than 0.5 DEG C) in sequence. The water retention rate can be greatly improved (≥98.7%) through step-by-step cooling. The water retention rate of the cooling structure using only a -15 DEG C refrigeration fin is only 92.3%. When the gas outlet temperature of the combustion furnace is high, preliminary cooling can be performed through the heat exchange pipe to further improve the water retention rate.

[0035] Preferably, the dehalogenator is internally provided with a red-hot copper wire with a temperature of 200-300 DEG C. The combustion furnace outlet gas contains excess oxygen. In the high-temperature oxygen atmosphere, halogen compounds (including organic halogen and inorganic halogen) are oxidized into copper chloride, thereby reducing the interference of halogen components in the soil on the determination of carbon and nitrogen contents. After the dehalogenator is used for a period of time (generally set as: 10 kg of cumulative soil determination), zinc powder and nitrogen gas are used to circulate and ventilate the dehalogenator at a dust gas concentration of 50 mg of zinc powder per liter of nitrogen gas. The reduction reaction is performed at 100-120 DEG C for 10-15 min. The copper wire after reduction is soaked in clean water for 10-15 min to remove the zinc chloride product, and then the copper wire is dried by a hair dryer to obtain a restored bright copper wire.

[0036] Preferably, the reduction furnace is provided with a copper-tungsten binary catalyst (CuWO x ), and the typical ratio is Cu 0.5 W 0.5 O x , the temperature window is 250-340℃, the NO conversion rate is >90%, the N2 selectivity is high, the nitrogen oxides are reduced to nitrogen at 250-340℃, the N2 and He mixed gas are obtained by separating CO2 through a carbon adsorption column, the nitrogen content is detected in TCD after natural cooling to 50-60℃ through a long pipeline, the thermal conductivity of N2 in the TCD detector is quite different from that of He, so that the nitrogen component concentration is tested, and the nitrogen concentration / test time curve is obtained according to the flow rate and test time of the test gas, and the nitrogen element content in the soil is obtained by integration and conversion, and the various carbon contents in the soil can be calculated in turn according to the N2 contents obtained at different combustion temperatures.

[0037] Preferably, the carbon adsorption column is provided with 5A molecular sieve, which can preferentially adsorb CO2 at less than 50℃, so as to separate N2 and CO2, when the nitrogen test is completed, desorption is carried out, He is introduced to discharge the nitrogen in the pipeline, and the carbon adsorption column is heated to 250℃ by the resistance wires around the carbon adsorption column to discharge the CO2 and He mixed gas, the CO2 content is detected in TCD after natural cooling to 50-60℃ through a long pipeline, and the various carbon contents in the soil can be calculated in turn according to the CO2 contents obtained at different combustion temperatures.

[0038] Preferably, the inner wall of the sulfur adsorption pipe is coated with an Ag2WO4 coating absorption pipe, which can perform a chemical adsorption reaction on the H2S gas produced by reduction at 200-250℃ (the waste heat of the reduction furnace tail gas can be directly utilized for direct reaction), and Ag2S is produced by the chemical adsorption reaction on the H2S gas produced by reduction at 200-250℃, so as to avoid the interference of S on the carbon and nitrogen tests of the soil with high sulfur content.

[0039] According to the previous research, the carbon elements in the soil mainly include organic carbon (low-temperature cracking temperature: 310℃±5℃), elemental carbon (medium-temperature oxidation temperature: 620℃±10℃), and carbonate (high-temperature combustion temperature: 930℃±20℃), the organic carbon, elemental carbon and a small part of carbonate are mainly derived from root systems, humus and bacterial components, and the carbonate is mostly derived from soil primary minerals, secondary minerals and fertilizers, so the present application designs segmented combustion detection to evaluate the soil fertility and water retention capacity and the like.

[0040] According to previous research, the nitrogen elements in the soil mainly include: ① microbial nitrogen (200-350 DEG C): mainly amino sugar nitrogen; ② organic nitrogen (350-550 DEG C): mainly amino acid nitrogen with biological activity; ③ inorganic nitrogen (> 700 DEG C): mainly ammonium or nitrate nitrogen, which is related to the nitrogen fertilizer condition of the soil. Under the condition of pure oxygen, the oxidation combustion reaction products of microbial nitrogen, organic nitrogen and inorganic nitrogen at the corresponding temperature are nitrogen oxide (NO x ) or nitrogen, so the contents of various nitrogen forms are tested by temperature segmentation.

[0041] Compared with the prior art, the beneficial effects of the present application are:

[0042] 1. The present application first uses segmented combustion detection, that is, through three-step method of low-temperature pyrolysis (310 DEG C), medium-temperature oxidation (620 DEG C) and high-temperature combustion (930 DEG C), the contents of organic carbon, elemental carbon, carbonate, microbial nitrogen, organic nitrogen and inorganic nitrogen and other forms are distinguished, and accurate data support is provided for soil improvement according to soil nutrient fertility indexes, and the research purposes of fertilization and agricultural improvement, differentiated fertilization and precision fertilization of different soils can be realized according to the differences in the contents of different elements or components.

[0043] 2. The present application uses three-stage refrigeration (10 DEG C, -5 DEG C, -15 DEG C) of electronic condenser combined with circulating gas drying, and the water retention rate is greater than or equal to 98.7%, which is significantly better than the traditional method. In addition to avoiding the negative effects of water on subsequent reactions, the water content of fresh soil can also be analyzed in real time with high precision, and the quantitative analysis time of the whole element (including water, carbon and nitrogen) is about 30-40 min. If only total carbon and total nitrogen are tested, it only takes 5-10 min. This is also the first time for quantitative analysis of fresh soil in the field, which improves the detection feedback efficiency.

[0044] 3. The present application eliminates the interference of water, halogen and sulfur by condensation dehydration, dehalogenator (red-hot copper wire) and sulfur adsorption tube (Ag2WO4 coating), respectively, improves the detection accuracy, and balances between detection accuracy and test real-time performance; At the same time, through the accurate measurement of the water content of the soil, the results of directly measured carbon and nitrogen elements are converted into the carbon and nitrogen contents in the dry soil, so as to avoid the negative effects of rain or irrigation on the true carbon and nitrogen contents of the soil.

[0045] 4. The present application combines the analysis of the contents of various carbon and nitrogen forms in the soil by previous people, and directly guides the water management, organic fertilizer / strain application and acid-base adjustment through the correlation analysis of the carbon and nitrogen form contents and the growth needs of crops, so as to improve the soil fertility, has the instant feedback effect of actual measurement implementation, avoids the disconnection between the test data and the soil management caused by climate change, and reduces the crop development loss caused by the existing detection errors. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 A flow chart of a method for detecting fresh soil carbon and nitrogen elements (horizontal placement) is provided for the present application. DETAILED DESCRIPTION

[0047] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments.

[0048] I. Research on soil carbon and nitrogen components:

[0049] According to previous research, carbon elements in soil mainly include organic carbon (low-temperature cracking temperature: 310℃±5℃), elemental carbon (medium-temperature oxidation temperature: 620℃±10℃), and carbonate (high-temperature combustion temperature: 930℃±20℃). Organic carbon, elemental carbon, and a small part of carbonate mainly come from components such as root systems, humus, and bacteria, and most of the carbonate comes from soil primary minerals, secondary minerals, and fertilizers. Therefore, the present application designs segmented combustion detection to evaluate soil fertility and water retention capacity and other conditions.

[0050] According to previous research, nitrogen elements in soil mainly include: ① microbial nitrogen (200-350℃): mainly amino sugar nitrogen; ② organic nitrogen (350-550℃): mainly amino acid nitrogen with biological activity; and ③ inorganic nitrogen (>700℃): mainly ammonium or nitrate nitrogen, which is related to soil nitrogen fertilizer conditions. Under pure oxygen conditions, the oxidation combustion reaction products of microbial nitrogen, organic nitrogen, and inorganic nitrogen at the corresponding temperatures are nitrogen oxides (NO x ) or nitrogen, so the content of various nitrogen forms is tested by temperature segmentation.

[0051] II. Detection method:

[0052] A method for detecting fresh soil carbon and nitrogen elements, comprising the following steps:

[0053] S1, pipe air exhaust:

[0054] A fresh soil sample (<3g) is placed in a combustion furnace, and oxygen is used at an inlet flow rate of 20-30mL / min to exhaust the combustion furnace, heat exchange pipe, electronic condenser, dehalogenizer, and flow divider. The exhaust gas is discharged from the exhaust port of the flow divider to the pipe, and the oxygen content in the pipe is >99%, and the exhaust port is closed.

[0055] S2, water quantification process:

[0056] Close the oxygen inlet, and close the heat exchange tube, so that the dehalogenator is in the non-working state, so that the combustion furnace, the electronic condenser, the dehalogenator and the flow divider form a circulating loop, the temperature of the combustion furnace is controlled to be 105±2℃, the electronic condenser condenses the volatile gas atmosphere, the gas circulates for 6-8min, the water content in the circulating gas at the bottom of the combustion furnace is less than 0.1%, and the water quality in the electronic condenser (the water gradually condenses in the liquid reservoir below the electronic condenser, the water volume is measured by a microliter pipette, and the condensed water quality is converted to obtain the water content in the soil) is recorded, and then divided by the weight of the soil sample, so as to obtain the water content in the soil. Generally, the water content of crops at the seedling stage is required to be 15-30%, so this is also a judgment condition for whether the soil needs irrigation;

[0057] By quantifying the soil moisture content, the directly measured carbon and nitrogen element results can be converted into the carbon and nitrogen contents in the dry soil. For example, if 2g of fresh soil has a water content of 20%, the nitrogen content obtained by the subsequent TCD after the present application is 50mg of nitrogen per gram of fresh soil, but the nitrogen content in the dry soil is:

[0058] (50mg / g x 2g) ÷ [(1-20%) x 2g] = 62.5mg of nitrogen per gram of dry soil;

[0059] That is, by accurately quantifying the soil moisture, the true carbon / nitrogen content of the soil can be tested, avoiding the problem that the carbon / nitrogen content is not accurately tested due to rain or irrigation of the soil.

[0060] S3, low-temperature cracking:

[0061] An oxygen inlet is adopted at an inlet flow rate of 50-60mL / min, the heat exchange tube is opened, the straight-through pipe between the combustion furnace and the electronic condenser is closed, and the straight-through pipe between the flow divider and the combustion furnace is closed. The pipe between the flow divider and the collector is opened, the oxygen inlet valve is closed, and the carrier gas inlet valve at the bottom of the combustion furnace is opened (so that the carrier gas drives the combustion tail gas into the flow divider);

[0062] The collector, the reduction furnace, the carbon adsorption column and the TCD detector are opened in sequence, carrier gas is introduced into one end of the collector, the carrier gas is He or Ar, and He is preferred. The dehalogenator is in the working state, the temperature of the combustion furnace is rapidly raised to 310℃±5℃, the reaction is carried out for 5-8min, the nitrogen content in the TCD detector after reduction, desulfurization and carbon adsorption is detected, which is converted into the microbial nitrogen content in the soil. The carbon dioxide in the carbon adsorption column is desorbed, and the carbon dioxide content in the TCD detector is detected, which is converted into the organic carbon content in the soil;

[0063] Under this temperature condition, the microbial nitrogen or other organic carbon in the soil reacts with pure oxygen and is catalytically reduced to generate N2 and CO2, and after adsorption by the carbon adsorption column, the nitrogen content detected by the TCD can be converted into the content of microbial nitrogen, and after desorption, the carbon content can be converted into the content of organic carbon. Generally, the microbial nitrogen (calculated as nitrogen) is 11-15 mg of nitrogen per kg of soil, and the organic carbon is 0.5-7.0% as the determination standard. If the organic carbon is insufficient, measures such as applying organic fertilizer and returning straw to the field can be taken to improve the organic matter. In addition to organic pollution, the higher the organic matter, the higher the soil fertility, such as the black soil in the northeast, which generally contains about 6% of organic matter;

[0064] S4, medium temperature oxidation:

[0065] An oxygen inlet flow of 80-100 mL / min is used, the heat exchange pipe is opened, the straight pipe between the combustion furnace and the electronic condenser is closed, the straight pipe between the shunt and the combustion furnace is closed, the pipe between the shunt and the collector is opened, the oxygen inlet valve is closed, the carrier gas inlet valve at the bottom of the combustion furnace is opened, the collector, the reduction furnace, the carbon adsorption column and the TCD detector are opened in sequence, and carrier gas is introduced into one end of the collector, which is He or Ar, preferably He, so that the dehalogenator is in working condition. The temperature of the combustion furnace is rapidly raised to 620℃±10℃, and the reaction is carried out for 5-7 min. After reduction, desulfurization and carbon adsorption, the nitrogen content in the TCD detector is detected, which is converted into the content of organic nitrogen in the soil. Then, the carbon dioxide in the carbon adsorption column is desorbed, and the carbon dioxide content in the TCD detector is detected, which is converted into the content of elemental carbon in the soil;

[0066] Under this temperature condition, the microbial nitrogen or other organic carbon in the soil reacts with pure oxygen and is catalytically reduced to generate N2 and CO2, and after adsorption by the carbon adsorption column, the nitrogen content detected by the TCD can be converted into the content of microbial nitrogen, and after desorption, the carbon content can be converted into the content of organic carbon. Generally, the microbial nitrogen (calculated as nitrogen) is 11-15 mg of nitrogen per kg of soil, and the organic carbon is 0.5-7.0% as the determination standard. If the organic carbon is insufficient, measures such as applying organic fertilizer and returning straw to the field can be taken to improve the organic matter. In addition to organic pollution, the higher the organic matter, the higher the soil fertility, such as the black soil in the northeast, which generally contains about 6% of organic matter;

[0067] S5, high temperature combustion:

[0068] The oxygen is used at an inlet flow rate of 70-90 mL / min, the heat exchange tube is opened, the straight-through tube between the combustion furnace and the electronic condenser is closed, the straight-through tube between the flow divider and the combustion furnace is closed, the tube between the flow divider and the collector is opened, the oxygen inlet valve is closed, the carrier gas inlet valve at the bottom of the combustion furnace is opened, the collector, the reduction furnace, the carbon adsorption column and the TCD detector are opened in sequence, and the carrier gas is introduced into one end of the collector, the carrier gas being He or Ar, preferably He, so that the dehalogenator is in working condition. The temperature of the combustion furnace is rapidly increased to ≥900℃ (generally, calcium carbonate is the main component of carbonates in soil, and 930±30℃ can be selected; when the content of barium or strontium in the soil is high, the temperature can be increased to 1350℃ or 1450℃ to reach the decomposition temperature of barium carbonate or strontium carbonate in the soil), the reaction is carried out for 3-5 min, the nitrogen content in the TCD detector after reduction, desulfurization and carbon adsorption is detected, which is converted into the organic nitrogen content in the soil, and then the carbon dioxide in the carbon adsorption column is desorbed, the carbon dioxide content in the TCD detector is detected, which is converted into the carbonate content in the soil;

[0069] Under this temperature condition, the inorganic nitrogen and carbonates in the soil react with pure oxygen and generate N2 and CO2 through catalytic reduction, and the nitrogen content detected by the TCD after adsorption by the carbon adsorption column can be converted into the content of inorganic nitrogen, and the carbon content after desorption can be converted into the content of carbonates. Generally, inorganic nitrogen (calculated as nitrogen) is 6-9 mg of nitrogen per kg of soil, and carbonates are 0-0.5% as the determination standard. If the inorganic nitrogen is insufficient, nitrogen fertilizer should be applied, and if it exceeds, nitrogen fertilizer can be temporarily not applied, and attention should be paid to the environmental problems caused by excessive nitrogen fertilizer. The content of carbonates can reflect the soil texture properties, and if the content exceeds 0.5%, the soil is easy to harden and cannot retain water and fertilizer. The content of carbonates in high-nutrient red soil or black soil accounts for less than 0.5% of the weight percentage of the soil. When it exceeds 0.5%, agricultural measures such as straw returning can be taken to change the soil structure;

[0070] According to the contents of organic carbon, carbonates, organic nitrogen and inorganic nitrogen, appropriate agricultural measures such as water, fertilizer, organic matter, acidity and alkalinity, and water and fertilizer retention rate are taken to improve the soil fertility and provide the conditions required for crop growth, thereby improving the yield of crops.

[0071] The flow divider has two outlets, one of which is a waste gas outlet, and the other of which is connected to the collector. The actual inlet gas amount into the detection section is controlled by the flow ratio of the two outlets. The flow divider controls 50% of the combustion gas to be detected into the detection section. When the nitrogen content in the soil detected by the detection section is 15 mg of nitrogen per g of soil, the actual nitrogen content in the soil is 15÷50%=30 mg of nitrogen per g of soil. This is because the soil with high nitrogen content may affect the working load of the reduction furnace and the upper limit of the TCD detection, thereby reducing the working saturation.

[0072] The following examples are set according to the above steps:

[0073] Example 1:

[0074] Northeastern black soil (high organic matter soil)

[0075] Sample information: Fresh black soil sample 2.5g, collected from farmland in Heilongjiang, not air-dried, directly detected.

[0076] Detection steps:

[0077] S1 (exhaust treatment): O2 flow 25 mL / min, exhaust to O2 content > 99%.

[0078] S2 (water quantification): 105°C cycle 7min, electronic condenser collects water 0.55g, moisture content = 22.0%.

[0079] S3 (low-temperature pyrolysis): 310°C pyrolysis for 6min, CO2 corresponding organic carbon = 6.1%, TCD detection of nitrogen = 1.1mg, converted microbial nitrogen = 14.2mg N / kg.

[0080] S4 (medium-temperature oxidation): 620°C oxidation for 6min, CO2 corresponding elemental carbon = 0.6%, TCD detection of nitrogen = 12.1mg, converted organic nitrogen = 57.3mg N / kg.

[0081] S5 (high-temperature combustion): 930°C combustion for 4min, CO2 corresponding carbonate = 0.3%, TCD detection of nitrogen = 1.1mg, inorganic nitrogen = 7.8mg N / kg.

[0082] Data analysis and recommendations:

[0083] High content of organic carbon (6.1%) and organic nitrogen (57.3mg / kg), consistent with the high fertility characteristics of black soil. Carbonate (0.3%) is consistent with the type and nature of the soil.

[0084] Example 2:

[0085] Southern red soil (low organic matter soil)

[0086] Sample information: Red soil sample 2.8g, collected from dry land in Jiangxi.

[0087] Test results:

[0088] Moisture content: 18.5%, organic carbon: 1.9%, microbial nitrogen: 10.8mg N / kg, organic nitrogen: 34.6mg N / kg, elemental carbon: 0.7%, carbonate: 0.4%;

[0089] Data analysis and recommendations:

[0090] Low organic carbon and organic nitrogen, need to supplement mature organic fertilizer (such as compost 5kg / m2 ) or inoculating nitrogen-fixing bacteria (such as rhizobium). The element carbon is moderate, and the water retention is good.

[0091] Example 3:

[0092] Saline-alkali soil (high carbonate soil)

[0093] Sample information: 3.0 g of saline-alkali soil was collected from a salinization area in Inner Mongolia.

[0094] According to the method of Example 1, the soil data is:

[0095] Carbonate content: 0.72%;

[0096] Inorganic nitrogen (ammonium or nitrate nitrogen): 9.5 mg N / kg;

[0097] Organic carbon: 2.3%;

[0098] Data analysis and recommendations:

[0099] It is proved to be a high carbonate soil, and soil remediation can be carried out according to the saline-alkali land improvement scheme.

[0100] According to the specific soil of Example 1, the following comparative examples are set up:

[0101] Comparative Example 1:

[0102] Traditional elemental analysis method (total carbon and nitrogen determination)

[0103] Method: The same as Example 1, except that the sample is dried before determination, and 950°C combustion is used directly without using step pyrolysis.

[0104] Problem:

[0105] Total carbon = 3.8% (cannot distinguish between organic carbon / carbonate).

[0106] Total nitrogen = 82 mg N / kg (cannot distinguish between microbial nitrogen / organic nitrogen).

[0107] Conclusion: Comparative Example 1 has a shorter test determination time, but the sample is ground after being dried for 5 days, and the specific composition of C / N cannot be judged. The traditional method cannot accurately guide the type of fertilization and timely guide fertilization.

[0108] Comparative Example 2:

[0109] The same as Example 1, except that a dehalogenator is not used,

[0110] Sample: Coastal beach soil (containing Cl - 1.2%),

[0111] Results:

[0112] TCD nitrogen and carbon dioxide signal abnormalities (chloride interferes with CO2 adsorption, NO x Reduction is inhibited by halogen.

[0113] Comparative Example 3:

[0114] The same as Example 1, except that a single-stage refrigeration (-15℃) is used instead of the three-stage refrigeration of Example 1,

[0115] Data analysis:

[0116] Single-stage refrigeration: water retention rate 92.1%, water quantitative error ±2.1%, subsequent carbon and nitrogen deviation +8%; three-stage refrigeration: water retention rate 98.9%, water quantitative error ±0.3%, subsequent carbon and nitrogen deviation +0.5%.

[0117] Mechanism analysis: single-stage refrigeration leads to water escape, affecting the performance of subsequent adsorbents.

[0118] The present application realizes the integration of "detection-regulation" by implementing Example 1-3 through segmented pyrolysis associated with soil improvement measures, and the detection error is controlled to be <1% by three-stage refrigeration + dehalogen design, verifying the accuracy and practicability of the method, while the comparative examples reveal the limitations of traditional methods. Combined with carbon and nitrogen form data and agronomic measures, soil management efficiency can be significantly improved.

[0119] Example 4:

[0120] The device of Example 1-3 and Comparative Example 1-3 is applied, which includes a combustion furnace, a heat exchange pipe, an electronic condenser, a dehalogenator, a flow divider, a collector, a reduction furnace, a carbon adsorption column, and a TCD detector.

[0121] The gas outlet of the combustion furnace is connected to the heat exchange pipe and the electronic condenser through a three-way valve, the other end of the heat exchange pipe is connected to the electronic condenser, and the heat exchange pipe is provided with circulating water at 5-30℃ for heat transfer wall heat conduction cooling. The obtained circulating water can also be used as a non-direct contact heat exchange medium between the electronic condenser and the dehalogenator to improve the dehalogenation efficiency.

[0122] The electronic condenser adopts a three-stage Peltier refrigeration fin combination structure, and the temperatures of the three-stage Peltier refrigeration fins are 10℃, -5℃ and -15℃ (error not more than 0.5℃) respectively. Through step-by-step cooling, the water retention rate can be greatly improved (≥98.7%), while the water retention rate of the cooling structure using only -15℃ refrigeration fin is only 92.3%. When the combustion furnace gas temperature is high, preliminary cooling can be performed through the heat exchange pipe to further improve the water retention rate.

[0123] The dehalogenizer is internally provided with hot copper wires with temperature of 200-300℃, the gas discharged from the combustion furnace contains excess oxygen, under the atmosphere of high-temperature oxygen, halogen compounds (including organic halogen and inorganic halogen) are oxidized into copper chloride, thereby reducing the interference of halogen components in soil on the determination of carbon and nitrogen content; after the dehalogenizer is used for a period of time (generally set as: 10 kg of cumulative determination amount of soil), the dehalogenizer is circulated and ventilated with dust gas of zinc powder and nitrogen gas with concentration of 50 mg zinc powder / L nitrogen gas, reduction reaction is carried out at 100-120℃ for 10-15 min, the reduced copper wires are taken out and soaked in clean water for 10-15 min to remove the zinc chloride product, and the recovered bright copper wires are dried by a blower.

[0124] The carrier gas component is introduced into the collector, the carrier gas is He or Ar, and He is preferred. The reducing atmosphere reduces the nitrogen oxides in the reduction furnace. The reduction furnace is internally provided with Pt / TiO2 reduction catalyst filler. The nitrogen oxides are reduced at 250-340℃ to obtain nitrogen gas. The thermal conductivity of nitrogen gas in the TCD detector is greatly different from that of He and trace H2, so the concentration of the nitrogen component is tested. According to the flow rate of the test gas and the test time, a nitrogen concentration / test time curve is obtained. After integration and conversion, the nitrogen content in the soil is obtained.

[0125] The reduction furnace is internally provided with a copper-tungsten binary catalyst (CuWO x ), and the typical ratio is Cu 0.5 W 0.5 O x . The temperature window is 250-340℃, the NO conversion rate is >90%, and the N2 selectivity is high. The nitrogen oxides are reduced at 250-340℃ to obtain nitrogen gas. N2 and He mixed gas is obtained after CO2 separation by a carbon adsorption column. The mixed gas is naturally cooled to 50-60℃ through a long pipeline and the nitrogen content is detected in the TCD. The thermal conductivity of N2 in the TCD detector is greatly different from that of He, so the concentration of the nitrogen component is tested. According to the flow rate of the test gas and the test time, a nitrogen concentration / test time curve is obtained. After integration and conversion, the nitrogen content in the soil is obtained. According to the N2 content obtained at different combustion temperatures, the various carbon contents in the soil can be sequentially calculated.

[0126] The carbon adsorption column is internally provided with 5A molecular sieve, which can preferentially adsorb CO2 at less than 50℃, so as to separate N2 and CO2. After the nitrogen test is completed, desorption is carried out, He is introduced to discharge the nitrogen in the pipeline, and the resistance wires around the carbon adsorption column are heated to 250℃ to discharge CO2 and He mixed gas. The mixed gas is naturally cooled to 50-60℃ through a long pipeline and the CO2 content is detected in the TCD. According to the CO2 content obtained at different combustion temperatures, the various carbon contents in the soil can be sequentially calculated.

[0127] Example 5:

[0128] On the basis of embodiment 4, a sulfur adsorption pipe can also be arranged between the reduction furnace and the carbon adsorption column, the inner wall of the sulfur adsorption pipe is coated with an Ag2WO4 coating absorption pipe, and H2S gas generated in reduction is subjected to chemical adsorption reaction at 200-250 DEG C to produce Ag2S, thereby avoiding the interference of S on the carbon and nitrogen tests of soil with high sulfur content.

[0129] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art in the technical range disclosed by the present application, according to the technical scheme and the inventive concept of the present application, equivalent replacement or change, should be covered in the protection scope of the present application.

Claims

1. A method for detecting carbon and nitrogen elements in fresh soil, characterized in that: The following steps are involved: S1, duct exhaust air: Place the fresh soil sample in a combustion furnace and use oxygen at an intake flow rate of 20-30 mL / min to exhaust the combustion furnace, heat exchange tube, electronic condenser, dehalogenator, and splitter. Exhaust gas is discharged from the exhaust port of the splitter until the oxygen content in the pipeline is greater than 99%, and then the exhaust port is closed; S2, water quantification process: Close the oxygen inlet and the heat exchange tube to disable the dehalogenator. Form a circulation loop with the combustion furnace, electronic condenser, dehalogenator, and diverter. Control the combustion furnace temperature to 105±2°C. Use the electronic condenser to condense the volatile atmosphere. Circulate the gas for 6-8 minutes. Ensure the water content of the circulating gas at the bottom of the combustion furnace is less than 0.1%. Record the water mass in the electronic condenser and divide it by the weight of the soil sample to obtain the water content in the soil. S3, low temperature cracking: Use oxygen at an intake flow rate of 50-60 mL / min, open the heat exchange tube, close the straight pipe between the combustion furnace and the electronic condenser, and close the straight pipe between the splitter and the combustion furnace, open the pipeline between the splitter and the collector, close the oxygen inlet valve, open the carrier gas inlet valve at the bottom of the combustion furnace, open the collector, reduction furnace, carbon adsorption column and TCD detector in sequence, and introduce carrier gas at one end of the collector, the carrier gas is He or Ar, the dehalogenator is put into working state, the combustion furnace temperature is rapidly increased to 310°C ± 5°C, the reaction is carried out for 5-8 minutes, and after reduction, desulfurization and carbon adsorption, the nitrogen content is detected in the TCD detector and converted into the microbial nitrogen content in the soil, and then the carbon dioxide in the carbon adsorption column is desorbed, and the carbon dioxide content is detected in the TCD detector and converted into the organic carbon content in the soil; S4, medium temperature oxidation: Using oxygen at an inlet flow rate of 80-100 mL / min, the combustion furnace temperature was rapidly raised to 620°C ± 10°C, and the reaction was carried out for 5-7 minutes. The nitrogen and carbon dioxide contents were detected in a TCD detector and converted into organic nitrogen and elemental carbon contents, respectively; S5, high temperature combustion: The combustion furnace temperature was rapidly raised to ≥900°C using oxygen at an inlet flow rate of 70-90 mL / min, and the reaction was carried out for 3-5 minutes. The nitrogen and carbon dioxide contents were detected in a TCD detector and converted into inorganic nitrogen and carbonate contents, respectively.

2. The method for detecting carbon and nitrogen elements in fresh soil according to claim 1, wherein By quantifying the moisture content of fresh soil, the directly measured carbon and nitrogen results are converted into the carbon and nitrogen content in dry soil. The moisture content of fresh soil with a mass of m is a%, and the nitrogen content obtained by TCD test is k0, with the unit of mg nitrogen / g fresh soil. The nitrogen content in dry soil is: k1=(k0×m)÷[(1-a%)×m], the unit is mg nitrogen / g dry soil.

3. A device for detecting carbon and nitrogen elements in fresh soil, applied to a method for detecting carbon and nitrogen elements in fresh soil according to claim 1 or 2, characterized in that: The device sequentially comprises a combustion furnace, a heat exchange tube, an electronic condenser, a dehalogenator, a splitter, a collector, a reduction furnace, a carbon adsorption column, a sulfur adsorption tube and a TCD detector.

4. The device for detecting carbon and nitrogen elements in fresh soil according to claim 3, characterized in that: The gas outlet of the combustion furnace is connected to the heat exchange tube and the electronic condenser through a three-way valve. The other end of the heat exchange tube is connected to the electronic condenser. Circulating water at 5-30°C is provided in the heat exchange tube for heat conduction and cooling of the heat transfer wall. The obtained circulating water is used as a non-direct contact heat exchange medium for the gas components between the electronic condenser and the dehalogenator to improve the dehalogenation efficiency.

5. The device for detecting carbon and nitrogen elements in fresh soil according to claim 3, characterized in that: The electronic condenser adopts a three-stage Peltier refrigeration plate combination structure, and the temperatures of the three-stage Peltier refrigeration plates are 10°C, -5°C and -15°C respectively. When the exhaust temperature of the combustion furnace is high, preliminary cooling is performed in advance through the heat exchange tube to improve the moisture retention rate.

6. The device for detecting carbon and nitrogen elements in fresh soil according to claim 3, characterized in that: A hot copper wire with a temperature of 200-300° C. is provided inside the dehalogenator. After the dehalogenator has been used for a period of time, zinc powder and nitrogen are used to circulate and ventilate the dehalogenator at a dust gas concentration of 50 mg zinc powder / L nitrogen. A reduction reaction is carried out at 100-120° C. for 10-15 minutes. The reduced copper wire is taken out and soaked in clean water for 10-15 minutes to remove zinc chloride products, and then dried with a hair dryer to obtain a restored and bright copper wire.

7. The device for detecting carbon and nitrogen elements in fresh soil according to claim 3, characterized in that: The reduction furnace is equipped with a copper-tungsten binary catalyst with a ratio of Cu 0.5 W 0.5 O x Nitrogen oxides are reduced at 250-340°C to obtain nitrogen, and CO2 is separated through a carbon adsorption column to obtain a mixture of N2 and He. After naturally cooling to 50-60°C through a long pipeline, the nitrogen content is detected in the TCD. The thermal conductivity of N2 in the TCD detector is quite different from that of He, so the concentration of the nitrogen component is tested, and the nitrogen concentration / test time curve is obtained according to the flow rate of the test gas and the test time. After integration and conversion, the nitrogen content in the soil is obtained. According to the N2 content obtained at different combustion temperatures, the various carbon contents in the soil can be measured in turn.

8. The device for detecting carbon and nitrogen elements in fresh soil according to claim 3, characterized in that: The carbon adsorption column is equipped with a 5A molecular sieve, which can preferentially adsorb CO2 at temperatures below 50°C, thereby separating N2 and CO2. After the nitrogen test is completed, desorption is carried out. During desorption, He is introduced into the nitrogen in the exhaust duct, and the resistance wires around the carbon adsorption column are used to heat it to 250°C to discharge the CO2 and He mixed gas. After naturally cooling to 50-60°C through a long pipeline, the CO2 content is detected in the TCD. According to the CO2 content obtained at different combustion temperatures, the various carbon contents in the soil can be measured in turn.

9. The device for detecting carbon and nitrogen elements in fresh soil according to claim 3, characterized in that: The inner wall of the sulfur adsorption tube is coated with an Ag2WO4 coating, and the H2S gas generated by reduction undergoes a chemical adsorption reaction at 200-250°C.

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