CN115060671B - Farmland ammonia volatilization box type multipoint synchronous in-situ real-time monitoring method based on laser spectrum technology - Google Patents
Farmland ammonia volatilization box type multipoint synchronous in-situ real-time monitoring method based on laser spectrum technology Download PDFInfo
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- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 title claims abstract description 356
- 238000012544 monitoring process Methods 0.000 title claims abstract description 199
- 229910021529 ammonia Inorganic materials 0.000 title claims abstract description 175
- 238000000034 method Methods 0.000 title claims abstract description 96
- 238000011065 in-situ storage Methods 0.000 title claims abstract description 22
- 238000005516 engineering process Methods 0.000 title claims abstract description 13
- 230000001360 synchronised effect Effects 0.000 title claims abstract description 13
- 238000001228 spectrum Methods 0.000 title claims abstract description 12
- 238000012360 testing method Methods 0.000 claims abstract description 37
- 238000012417 linear regression Methods 0.000 claims abstract description 12
- 238000005259 measurement Methods 0.000 claims description 36
- 239000002689 soil Substances 0.000 claims description 10
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 8
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 6
- 238000004364 calculation method Methods 0.000 claims description 5
- 229910052757 nitrogen Inorganic materials 0.000 claims description 3
- 230000000630 rising effect Effects 0.000 claims description 2
- 229910000069 nitrogen hydride Inorganic materials 0.000 claims 1
- 238000012216 screening Methods 0.000 claims 1
- 238000005070 sampling Methods 0.000 abstract description 26
- 230000035945 sensitivity Effects 0.000 abstract description 2
- 239000007789 gas Substances 0.000 description 11
- 230000003068 static effect Effects 0.000 description 9
- 238000000605 extraction Methods 0.000 description 7
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 6
- 238000010521 absorption reaction Methods 0.000 description 5
- BFNBIHQBYMNNAN-UHFFFAOYSA-N ammonium sulfate Chemical compound N.N.OS(O)(=O)=O BFNBIHQBYMNNAN-UHFFFAOYSA-N 0.000 description 5
- 229910052921 ammonium sulfate Inorganic materials 0.000 description 5
- 235000011130 ammonium sulphate Nutrition 0.000 description 5
- 238000011160 research Methods 0.000 description 5
- 238000009825 accumulation Methods 0.000 description 4
- 239000002253 acid Substances 0.000 description 4
- 230000008859 change Effects 0.000 description 4
- 238000013461 design Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 230000004907 flux Effects 0.000 description 4
- 238000009423 ventilation Methods 0.000 description 4
- 238000011156 evaluation Methods 0.000 description 3
- 238000012827 research and development Methods 0.000 description 3
- UIIMBOGNXHQVGW-UHFFFAOYSA-M Sodium bicarbonate Chemical compound [Na+].OC([O-])=O UIIMBOGNXHQVGW-UHFFFAOYSA-M 0.000 description 2
- 241000209140 Triticum Species 0.000 description 2
- 235000021307 Triticum Nutrition 0.000 description 2
- 230000002745 absorbent Effects 0.000 description 2
- 239000002250 absorbent Substances 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 238000002474 experimental method Methods 0.000 description 2
- 238000009863 impact test Methods 0.000 description 2
- 238000000691 measurement method Methods 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 238000001179 sorption measurement Methods 0.000 description 2
- 240000008042 Zea mays Species 0.000 description 1
- 235000016383 Zea mays subsp huehuetenangensis Nutrition 0.000 description 1
- 235000002017 Zea mays subsp mays Nutrition 0.000 description 1
- 238000000862 absorption spectrum Methods 0.000 description 1
- -1 ammonium ions Chemical class 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 239000008358 core component Substances 0.000 description 1
- 230000001186 cumulative effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 239000003337 fertilizer Substances 0.000 description 1
- 230000006870 function Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000012625 in-situ measurement Methods 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 235000009973 maize Nutrition 0.000 description 1
- 230000003446 memory effect Effects 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 239000003895 organic fertilizer Substances 0.000 description 1
- 238000004445 quantitative analysis Methods 0.000 description 1
- 238000010223 real-time analysis Methods 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 229910000030 sodium bicarbonate Inorganic materials 0.000 description 1
- 235000017557 sodium bicarbonate Nutrition 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 238000011282 treatment Methods 0.000 description 1
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Abstract
The invention discloses a farmland ammonia volatilization box type multipoint synchronous in-situ real-time monitoring method based on a laser spectrum technology, which is used for farmland community comparison test ammonia volatilization monitoring. According to the method, a farmland ammonia volatilization in-situ monitoring system of a laser multi-reflection light path is adopted to monitor ammonia volatilization in comparison tests of cells, and a monitoring box is arranged in each test cell and used for monitoring ammonia volatilization; the monitoring adopts an intermittent closed monitoring mode, and the ammonia concentration, the air pressure and the air temperature in all monitoring boxes are synchronously monitored; and after the continuous monitoring data in each monitoring period are checked and screened by a linear regression equation, calculating the ammonia volatilization rate based on a dynamic closed box method theory. The method can realize multipoint synchronization, in-situ real-time online monitoring of ammonia volatilization of farmland cell contrast test with high sensitivity and high time resolution, avoid sampling errors and improve comparability of monitoring data.
Description
Technical Field
The invention relates to a farmland cell comparison test ammonia volatilization monitoring method, in particular to a farmland ammonia volatilization box type multipoint synchronous in-situ real-time monitoring method based on a laser spectrum technology.
Background
Since the 70 s of the last century, numerous scientists have made efforts to establish various types of farmland ammonia volatilization measurement methods, but there are large differences in applicability, accuracy, space-time resolution, and the like. Currently, the mainstream farmland ammonia volatilization measurement methods can be divided into two types, namely a microclimate method and a box method. The box-type method is the most main method for determining ammonia volatilization by farmland cell contrast test. The box type method is generally classified into a closed box type method and an open box type method according to whether the sampling box is communicated with the outside air. The closed box method is to directly measure the ammonia value added in the air in the closed sampling box within a certain time to calculate ammonia volatilization, and can be divided into a static closed box method and a dynamic closed box method according to the ammonia value added measuring method; the static airtight box method is to place an acid absorbent in the airtight box to continuously absorb volatile ammonia gas to measure ammonia volatilization flux, and the dynamic airtight box method is based on the assumption that the concentration of the volatile gas in the airtight box is linearly increased along with time, and the ammonia volatilization flux is measured by measuring the ammonia concentration at the beginning and the end of the airtight box; due to the limitation of detection technology, the existing ammonia volatilization detection mostly adopts a static closed box method, and the dynamic closed box method has less application. The open tank method is to pump out ammonia gas in the sampling tank at a stable flow rate by using a suction pump and enrich and measure the ammonia volatilization flux by using an acid absorbent, and is also called as a suction tank method. The static closed box method and the open box method which are commonly used at home and abroad rely on an acid absorption method to enrich soil volatile ammonia (generally obtain one sample in 12-24 hours), are time-consuming and labor-consuming, have low time resolution, and are difficult to reveal the daily dynamic change rule of ammonia volatilization. The conventional analysis technology is difficult to realize accurate and rapid online monitoring of the ammonia concentration, and limits the improvement of the ammonia volatilization research level of farmlands.
The tunable laser absorption spectrum technology utilizes the fingerprint characteristic of a molecular spectrum, and realizes quantitative analysis of gas concentration by acquiring the absorption information of the detected gas on the characteristic spectrum, thereby having the characteristics of high spectral resolution, high sensitivity, good selectivity and the like, and being one of effective methods for rapid and real-time analysis of trace gas. The method comprises two measurement modes of an open light path and a gas absorption tank, wherein the measurement mode of the gas absorption tank is suitable for gas sampling or in-situ measurement of a point to be measured, and is a necessary choice for ammonia volatilization measurement in a cell contrast test. The method is characterized in that a box-type ammonia volatilization real-time monitoring system which can be used for a district comparison test is developed by combining a cavity enhancement laser spectrum technology from a gas absorption tank and a dynamic closed box method abroad, one ammonia analyzer needs to be matched with a plurality of sampling boxes for use in farmland application, the plurality of sampling boxes are sequentially subjected to circulating air suction sampling measurement, monitoring data are asynchronous, for example, when one ammonia concentration analyzer is matched with 16 sampling boxes for circulating monitoring, the 1 st sampling box monitoring time and the 16 th sampling box monitoring time are separated by 4 hours, the difference of measurement results is larger due to the change of meteorological factors in 4 hours, the problems that the measurement time resolution of a single sampling box is low (6 data/day), the measurement result time of the plurality of sampling boxes is poor are solved, and the number of the sampling boxes is larger, and the single-point time resolution and the multi-point data are poor in comparability are solved; in the process of air extraction sampling measurement, the inner wall of the ammonia gas adsorption pipeline with high adsorptivity can cause larger sampling error and memory effect; the high-precision resonant cavity of the instrument core component has extremely high requirements on the monitoring environment and needs frequent laboratory calibration.
Disclosure of Invention
The invention aims to provide a box-type multi-point synchronous in-situ real-time monitoring method for ammonia volatilization in farmland based on a laser spectrum technology, which aims to overcome the defects of the box-type method for ammonia volatilization measurement in the conventional farmland cell comparison test, realize synchronous in-situ real-time monitoring of ammonia volatilization in all cells in the farmland cell comparison test and solve the problems of low single-point time resolution and poor multi-point data comparability in the conventional method.
The aim of the invention is achieved by the following technical scheme:
1. a farmland ammonia volatilization box type multipoint synchronous in-situ real-time monitoring method based on a laser spectrum technology is characterized by comprising the following steps:
(1) A monitoring box is arranged in each monitoring area and used for monitoring ammonia volatilization, and the ammonia volatilization value of the monitoring box is regarded as the ammonia volatilization value in the monitoring area;
(2) The monitoring adopts an intermittent closed monitoring mode, and the ammonia concentration C, the air pressure p and the air temperature T in all monitoring boxes are synchronously monitored;
(3) After the continuous monitoring data in each monitoring period are checked and screened by a linear regression equation, the ammonia volatilization rate Q (kg N ha –1 d–1) is calculated based on a dynamic closed box method theory, and the calculation formula is as follows
In the formula (1)The absolute concentration of ammonia in the monitoring box is measured, the unit of the absolute concentration of ammonia in the monitoring box is ppm, the unit of the p is the air pressure in the monitoring box is hPa, the unit of the absolute temperature of air in the monitoring box is K, the unit of the absolute temperature of the air in the monitoring box is K, the unit of the molecular weight of ammonia is 17, and the unit of the molecular weight of air is 28.97;
K in the formula (2) is a regression coefficient of a linear regression equation of ammonia concentration and time, V is the inner volume of the monitoring box, the unit is m 3, A is the inner horizontal cross section area of the monitoring box, namely the area of the covered monitoring soil, the unit is m 2, 14 is nitrogen atomic weight, and 17 is ammonia molecular weight;
The intermittent closed monitoring mode is that each monitoring period is 20-40 minutes, the cover closing measurement time is 2-3 minutes, the monitoring box is automatically closed within the time from 0 to 2-3 minutes, the ammonia concentration, the air pressure and the air temperature in the box are continuously monitored in situ, the cover of the monitoring box is opened and ventilated with the external environment in the rest time of the monitoring period, and the next monitoring period is entered after the end; all the monitoring boxes are set to be synchronously monitored. Taking a monitoring period of 20 minutes, a cover closing measurement time of 3 minutes as an example, performing cover closing monitoring for 0-3 minutes, and uncovering and ventilation for 4-20 minutes to form a first monitoring period; and (3) closing the cover for monitoring 21-23 minutes, opening the cover for ventilation for 24-40 minutes, forming a second monitoring period, and so on.
Preferably, when the monitoring box is arranged in the step a, if ammonia volatilization of a paddy field is monitored, after the monitoring box is inserted into soil, the height of the residual box above the water surface is 25+/-3 cm, the monitoring box is ensured to be horizontally placed, water is injected into the monitoring box until the height of the box above the water surface is 25+/-3 cm during the monitoring period, and the height of the box above the water surface is measured; if the ammonia volatilization in the dry land is monitored, the ground surface on which the monitoring box is installed is firstly repaired to be horizontal, then the monitoring box is inserted into soil, the height of the residual box body above the ground surface is 25+/-3 cm, the monitoring box is ensured to be horizontally placed, and the height of the box body above the ground surface is measured.
Preferably, the monitoring in the step (2) is set to automatically store the monitoring data once within 1-5 seconds.
Preferably, the continuous monitoring data in each monitoring period in the step (3) is that after being checked and screened by a linear regression equation: firstly, establishing absolute concentration of ammonia gasUnitary linear regression equation with time t (d)/>Wherein the decision coefficient R 2 =θ, where k is a regression coefficient and b is a constant term; when the theta is more than or equal to 0.95, the ammonia concentration is regarded as linearly rising along with time, and the ammonia volatilization rate can be calculated, if the theta is less than 0.95, the last 10 seconds of monitoring data in continuous 3 minutes of monitoring data are sequentially removed, and the removal is finished until the theta is more than or equal to 0.95, and the remaining data are used for calculating the ammonia volatilization rate.
Preferably, the ammonia volatilization rate calculated by each closed lid monitoring data in the step (3) is taken as an average value of the ammonia volatilization rate in each monitoring period.
The invention has the beneficial effects that:
1. Compared with the traditional box-type method, the method disclosed by the invention has the advantages that the laser spectrum technology is adopted, the ammonia concentration is monitored in situ on line in real time, and the defect that the ammonia is easy to adsorb the pipe wall to cause sampling errors is avoided; the time resolution is greatly improved, and the dynamic change in the ammonia volatilization day can be monitored; by adopting the intermittent cover closing monitoring method, the disturbance to the volatile environment is greatly reduced, and the measurement result is closer to the real natural environment.
2. Compared with the foreign box-type ammonia volatilization real-time monitoring method, the method provided by the invention realizes synchronous monitoring of ammonia volatilization by all monitoring boxes, the time resolution (72 data/day) of monitoring data of a single monitoring box and the comparability of monitoring data of a plurality of monitoring boxes are greatly improved, and the single-point time resolution and the comparability of multi-point data are not influenced by the number of the monitoring boxes.
Drawings
FIG. 1 monitors the effect of tank height on process accuracy.
Fig. 2 shows the effect of closing monitoring time on ammonia concentration accumulation law.
FIG. 3 monitors the effect of interval time on the accuracy of the method.
FIG. 4 reliability assessment of ammonia volatilization for the method of the invention and other box-type methods.
Fig. 5 is a schematic diagram of the monitoring tank of the present invention measuring ammonia concentration.
Detailed Description
The following is a clear and complete description of the technical solutions according to embodiments of the present invention, with reference to the accompanying drawings, and it is apparent that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1: farmland ammonia volatilization box type multipoint synchronous in-situ real-time monitoring method based on laser spectrum technology
1. Test design
A farmland ammonia volatilization in-situ sampling device (utility model patent, CN 202021342933.6) of a laser multiple reflection light path developed by the institute of optical precision machinery of Anhui of China academy of sciences is adopted to measure farmland ammonia volatilization. Research and development experiments are carried out in farmland in China academy of sciences Fengqiu farmland ecosystem national field scientific observation research station. The method comprises the steps of adopting an ammonium sulfate solution as a simulated ammonia volatilization source, starting ammonia volatilization by a weak base sodium bicarbonate solution at the beginning of a test, ending ammonia volatilization by a strong acid dilute sulfuric acid solution at the end of the test, calculating the volatilization rate of the volatilization source by measuring the content of ammonium ions in the solution before and after the test, and comparing the measurement result with the measurement result of the method of the utility model to evaluate the accuracy of the method. The method research and development is divided into three parts:
1) Impact test of monitoring tank height on method accuracy: ammonia is lighter than air, and the upward diffusion of soil volatile ammonia can lead to ammonia concentration to produce vertical gradient change, so monitoring box body height can influence experimental result, needs to evaluate. The monitoring box was set at three different heights of 25cm, 37.5cm, 50cm, 3 replicates each. A simulated ammonia volatilization source is manufactured by using 0.01mol/L ammonium sulfate solution, weak base is added immediately after the simulated ammonia volatilization source is placed into a monitoring box to start ammonia volatilization, a farmland ammonia volatilization in-situ sampling device adopting a laser multi-reflection light path is used for monitoring ammonia concentration, air pressure and air temperature in the box, the monitoring interval time is set to be 30 minutes, the cover closing monitoring time is set to be 5 minutes, monitoring data are automatically stored once in 1 second, and after continuous monitoring is carried out for 12 hours, dilute sulfuric acid solution is added to finish ammonia volatilization. The influence of different box heights on the accuracy of measuring ammonia volatilization by the method is studied, and the optimal box height is determined.
2) Impact test of closing monitoring time on ammonia concentration accumulation law: according to the test 1) results, the monitoring box is set to the optimal height, and 2 simulated ammonia volatilization sources with different volatilization rates are respectively prepared by using 0.01mol/L and 0.02mol/L of ammonium sulfate solution, and 3 repetitions are respectively set. And (3) immediately adding weak base to start ammonia volatilization after the simulated ammonia volatilization source is placed into a monitoring box, monitoring the ammonia concentration in the box by adopting a farmland ammonia volatilization in-situ sampling device of a laser multi-reflection light path, wherein the monitoring interval time is set to be 20 minutes, the cover closing monitoring time is set to be 15 minutes, the monitoring data is automatically stored once in 1 second, and the continuous monitoring is carried out for 12 hours. And researching the influence of the closing monitoring time on the ammonia concentration accumulation rule, and determining the optimal closing monitoring time.
3) Monitoring the influence test of the interval time on the accuracy of the method: setting the monitoring box to be the optimal height according to the result of the test 1), setting the optimal cover closing monitoring time according to the result of the test 2), setting four different monitoring intervals of 20 minutes, 40 minutes, 60 minutes and 120 minutes, and setting 3 repetitions of each monitoring interval. A simulated ammonia volatilization source is manufactured by using 0.01mol/L ammonium sulfate solution, weak base is added immediately after the simulated ammonia volatilization source is placed into a monitoring box to start ammonia volatilization, a farmland ammonia volatilization in-situ sampling device of a laser multi-reflection light path is adopted to monitor ammonia concentration, air pressure and air temperature in the box, monitoring data are automatically stored once in 1 second, and after continuous monitoring is carried out for 12 hours, dilute sulfuric acid solution is added to finish ammonia volatilization. And researching the influence of the monitoring interval time on the accuracy of the method, and determining the optimal monitoring interval time.
2. Ammonia volatilization calculation
The monitored ammonia volume concentration C (ppm) is converted into absolute concentrationConverting the formula intoWhere p is the monitor in-tank air pressure (hPa), T is the monitor in-tank air absolute temperature (K), 17 is the ammonia molecular weight, and 28.97 is the air molecular weight.
Establishing absolute concentration of ammonia gasUnitary linear regression equation with time t (d)Wherein the decision coefficient R 2 =θ, where k is a regression coefficient and b is a constant term; and if the theta is more than or equal to 0.95, the group of data can be used for calculating the ammonia volatilization rate, if the theta is less than 0.95, the last 10 seconds of monitoring data in the monitoring data are sequentially removed, the removal is finished until the theta is more than or equal to 0.95, and the rest data are used for calculating the ammonia volatilization rate.
The calculation formula of the ammonia volatilization rate Q (kg N ha –1 d–1) isWhere k is the regression coefficient of the linear regression equation of ammonia concentration and time, V is the monitoring tank internal volume (m 3), A is the monitoring tank internal horizontal cross-sectional area (i.e. the area of the covered monitored soil, m 2, the monitoring tank horizontal cross-sectional area used in this test is 0.205m 2), 14 is the nitrogen atomic weight, and 17 is the ammonia molecular weight. The ammonia volatilization rate calculated by the closed cover monitoring data in each monitoring period is taken as an average value of the ammonia volatilization rates in the whole monitoring period, and the ratio of the average value of the ammonia volatilization rates in all monitoring periods of each test single monitoring box to the actual ammonia volatilization rate of the simulated volatilization source is taken as the method measurement accuracy (recovery rate).
3. Test results
Monitoring the ammonia concentration in the tank does not linearly increase all the time, and when the partial pressure of the ammonia in the tank gradually increases along with the increase of the ammonia concentration, the ammonia concentration gradually becomes curve-increased until reaching saturation, which can lead to flux calculation errors; too low a height of the monitoring box disturbs the ammonia volatilization environment too much, and the ammonia concentration can reach saturation faster, and too high a height can lead to uneven ammonia gas space distribution so as to increase measurement errors. It is therefore necessary to study the effect of different monitor tank heights on the accuracy of the method to determine the optimal tank height. As shown in FIG. 1, the measurement accuracy of the method is remarkably reduced as the height of the monitoring box body is increased, and the accuracy is highest when the height in the box body is 25 cm. In order to ensure accuracy, when ammonia volatilization is monitored in the field, the height in the monitoring box is set to 25+/-3 cm, and a box height design of 25cm is adopted in the subsequent test.
The method is based on a dynamic closed box method for measuring farmland ammonia volatilization, and the principle is that the ammonia concentration in the closed box is assumed to linearly rise along with time, and the ammonia volatilization is calculated by measuring the increment of the gas concentration in the closed box in unit time. However, in practice, the ammonia concentration increases linearly with time in a short period of time, but in the later period, the ammonia concentration curve increases until saturation due to the increase of the ammonia concentration (the partial pressure of ammonia in air increases), so that the reliability of calculating the ammonia volatilization rate is highest by selecting the ammonia concentration monitoring data of the period of time of linearly increasing the ammonia concentration with time. Therefore, the influence of the closing monitoring time on the ammonia concentration accumulation rule is designed to be researched by the test so as to formulate the optimal closing monitoring time. As shown in fig. 2a, the ammonia concentration at different volatilization rates was monitored continuously for 15 minutes after closing the lid, and then the ammonia concentration was raised linearly until reaching a cumulative law close to saturation. As shown in FIG. 2b, the regression equation is used for judging that the coefficient R2 is more than or equal to 0.95 when the closing monitoring time is within 3 minutes through linear regression equation fitting, namely, the ammonia concentration is regarded as linearly increasing; as shown in fig. 2c, R2<0.95 at 4 minutes, i.e. the ammonia concentration has been shifted to a curve rise; therefore, when the ammonia volatilization is monitored in the field, the monitoring time for closing the cover of the monitoring box is properly set within 2-3 minutes. The closing monitoring time was set to 3 minutes in the following experiments.
The intermittent closed monitoring mode adopted by the method is that after the continuous cover closing monitoring is carried out for 3 minutes, the cover opening ventilation is carried out for a certain time, and the sum of the cover closing monitoring time and the cover opening ventilation time is a monitoring interval time. The monitoring interval time is too long, the time representativeness of the monitoring data is poor, and the measurement accuracy is affected; too short monitoring interval time, too frequent opening and closing of the cover greatly disturb the ammonia volatilization environment, and the authenticity of the measurement result is affected. Therefore, the influence of the monitoring interval time on the accuracy of the method is designed for the experimental study so as to formulate the optimal monitoring interval time. As shown in fig. 3, the measurement accuracy of the method is significantly reduced as the monitoring interval increases, the accuracy is highest when the monitoring interval is 20 minutes, and the measurement result error mainly depends on the time representativeness of the monitoring data. Thus, when ammonia volatilization is monitored in the field, the monitoring interval time is set to be 20-40 minutes, and the monitoring interval time of 20 minutes is adopted for design in the subsequent test.
Based on the three research and development tests, the application standard of the method is formulated. Example 2: reliability assessment method for farmland ammonia volatilization box type multipoint synchronous in-situ real-time monitoring method based on simulated ammonia volatilization source
1. Test design
The method is adopted to evaluate the ammonia volatilization by comparing with a static closed box method and an exhaust box method which are commonly used for domestic farmland community comparison test ammonia volatilization measurement and a foreign box type ammonia volatilization real-time monitoring system (Model 911-0011,Los Gatos Research,California, which is called as LGR instrument hereinafter). The static closed box method adopted in the test is described in Wang Chaohui, etc., in-situ determination of ammonia volatilization of northern winter wheat/summer maize rotation system, ecological journal, 2002, volume 22, 3: 359-365", see' Ni Kang et al for the extraction box method, the research on the quaternary ammonia volatilization loss of the soil wheat and the influence factors thereof for the long-term positioning test of the organic and inorganic fertilizer, 2009, volume 28, 12, 2614-2622). Simulated ammonia volatilization source application method referring to example 1,2 simulated ammonia volatilization sources with different volatilization rates are respectively manufactured by using 0.01mol/L and 0.02mol/L ammonium sulfate solution, 3 repeated monitoring boxes for measuring each volatilization rate are respectively arranged for continuous monitoring for 12 hours; meanwhile, 3 simulated ammonia volatilization sources with different volatilization rates are respectively arranged in the natural environment, and the accuracy of the measurement of the different box methods is represented by the ratio of the measured ammonia volatilization rate by the different box methods to the actual ammonia volatilization rate in the natural environment. The evaluation test is carried out in farmland in national science observation and research station of China academy of sciences Fengqiu farmland ecosystem.
2. Test results
As shown in FIG. 4a, the accuracy of the method for measuring the ammonia volatilization rate is significantly higher than that of other methods, which shows that the measurement result is closest to the ammonia volatilization in the real natural environment, mainly because the intermittent closed monitoring mode adopted by the method has less disturbance to the environment and is closer to the natural environment. The static closed box method is used for continuously monitoring in a closed manner, so that the ammonia volatilization environment is severely disturbed, and the difference between the static closed box method and the natural environment is great, so that the measuring result and the ammonia volatilization in the natural environment are great; although the exhaust box method is intermittent air extraction and sampling, the air extraction box method needs to be closed for air extraction for 4 hours, and the air pressure difference between the inside and outside of the sampling box caused by long-time cover closing and air extraction seriously disturbs the ammonia volatilization environment; the intermittent closed monitoring mode adopted by the foreign box-type ammonia volatilization real-time monitoring system has small disturbance to the environment, but the time resolution of a single sampling box is low, and the accuracy of the measurement result is reduced due to the ammonia adsorption error in the air exhaust pipeline.
The box-type method has the main function of being used for comparing and measuring the ammonia volatilization rates under different test treatments in the cell test, and the reliability of the comparison measurement is also an important index for evaluating the box-type method. In the evaluation test, the ratio of the measurement results of the simulated ammonia volatilization sources with different volatilization rates is measured by different box methods, and is compared with the actual volatilization rate ratio of the simulated ammonia volatilization sources with different volatilization rates in the natural environment, so that the reliability of the comparison measurement of the different box methods is evaluated. As shown in fig. 4b, the comparison result of the volatilization rates of different ammonia volatilization sources measured by the method of the invention is not significantly different from the natural environment, mainly because the measurement result of the method of the invention is close to the natural environment, all monitoring boxes synchronously monitor, and the measurement results are synchronously comparable. The static closed box method and the air extraction box method have significant differences between the comparison and measurement results and the natural environment because of large disturbance to the ammonia volatilization environment. The measurement results of the LGR apparatus in the united states are also significantly different from the natural environment, mainly because a plurality of sampling boxes sequentially circulate asynchronous measurement, and the measurement data time of different sampling boxes is poor in comparability.
In conclusion, the simulated ammonia volatilization source evaluation test shows that compared with the traditional box-type method and foreign instruments, the accuracy of measuring the ammonia volatilization of the comparison test of the farmland cell by the method is obviously improved, the comparison measurement result is closer to the actual field situation, the reliability is obviously improved, and the advancement and the effectiveness of the method are proved.
Claims (3)
1. A farmland ammonia volatilization box type multipoint synchronous in-situ real-time monitoring method based on a laser spectrum technology is characterized by comprising the following steps:
(1) A monitoring box is arranged in each monitoring area for monitoring ammonia volatilization;
(2) The monitoring adopts an intermittent closed monitoring mode, and the ammonia concentration C, the air pressure p and the air temperature T in all monitoring boxes are synchronously monitored;
(3) After the continuous monitoring data in each monitoring period are checked and screened by a linear regression equation, the ammonia volatilization rate Q is calculated based on a dynamic closed box method theory, the unit is kg N ha –1d–1, and the calculation formula is that
In the formula (1)The absolute concentration of ammonia in the monitoring box is measured in kg m –3, the concentration of ammonia in the monitoring box is measured in ppm, the pressure of air in the monitoring box is measured in p, the absolute temperature of air in the monitoring box is measured in hPa, the absolute temperature of air in the monitoring box is measured in T, the molecular weight of ammonia is measured in K, and the molecular weight of air is measured in 28.97;
K in the formula (2) is a regression coefficient of a linear regression equation of ammonia concentration and time, V is the inner volume of the monitoring box, the unit is m 3, A is the inner horizontal cross section area of the monitoring box, namely the area of the covered monitoring soil, the unit is m 2, 14 is nitrogen atomic weight, and 17 is ammonia molecular weight;
The intermittent closed monitoring mode is that each monitoring period is 20-40 minutes, the cover closing measurement time is 2-3 minutes, the monitoring box is automatically closed within the time from 0 to 2-3 minutes, the ammonia concentration, the air pressure and the air temperature in the box are continuously monitored in situ, the cover of the monitoring box is opened and ventilated with the external environment in the rest time of the monitoring period, and the next monitoring period is entered after the end; all monitoring boxes are set to synchronously monitor;
In the step a, when the monitoring box is arranged, if ammonia volatilization of a paddy field is monitored, after the monitoring box is inserted into soil, the height of the residual box above the water surface is 25+/-3 cm, the monitoring box is ensured to be horizontally placed, water is injected into the monitoring box until the height of the box above the water surface is 25+/-3 cm during the monitoring period, and the height of the box above the water surface is measured; if the ammonia volatilization in the dry land is monitored, the ground surface on which the monitoring box is installed is firstly repaired to be horizontal, then the monitoring box is inserted into soil, the height of the residual box above the ground is 25+/-3 cm, the monitoring box is ensured to be horizontally placed, and the height of the box above the ground is measured;
the continuous monitoring data in each monitoring period in the step (3) is subjected to linear regression equation test screening and then is: firstly, establishing a unitary linear regression equation of absolute ammonia concentration rho NH3 with time t (d) in kg m –3 Wherein the decision coefficient R 2 =θ, where k is a regression coefficient and b is a constant term; when the theta is more than or equal to 0.95, the ammonia concentration is regarded as linearly rising along with time, and the ammonia volatilization rate can be calculated, if the theta is less than 0.95, the last 10 seconds of monitoring data in continuous 3 minutes of monitoring data are sequentially removed, and the removal is finished until the theta is more than or equal to 0.95, and the remaining data are used for calculating the ammonia volatilization rate.
2. The farmland ammonia volatilization box type multipoint synchronous in-situ real-time monitoring method according to claim 1, which is characterized in that: and (3) setting 1-5 seconds to automatically store monitoring data once during monitoring in the step (2).
3. The farmland ammonia volatilizing box type multipoint synchronous in-situ real-time monitoring method according to any one of claims 1-2, characterized in that: the ammonia volatilization rate calculated by each closed cover monitoring data in the step (3) is taken as an average value of the ammonia volatilization rate in each monitoring period.
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