A method for simultaneously measuring soil n2o emission and nh3 volatilization

Abstract

The present application belongs to the technical field of agrochemistry and soil ecology, and particularly relates to a method for simultaneously measuring soil N2O emission and NH3 volatilization. First, the soil sample is subjected to aerobic culture, and then subjected to closed treatment for 24 hours, and the N2O concentration and the NH3 concentration are simultaneously measured under the same culture system condition. The method of the present application performs soil aerobic culture under the same culture condition, realizes spatial separation and collection of N2O and NH3 by setting a headspace gas collection structure on the top of the culture container and setting an acidic absorption unit inside the culture container, and simultaneously measures the two gaseous nitrogen through periodic closed culture operation within the same culture time scale.

Description

Technical Field

[0001] This invention belongs to the field of agricultural chemistry and soil ecology, specifically relating to a method for simultaneously measuring soil N2O emissions and NH3 volatilization. Background Technology

[0002] In the process of nitrogen cycle in farmland soil, N2O emission and NH3 volatilization are two important pathways for the loss of gaseous nitrogen, which not only affect fertilizer nitrogen use efficiency, but also have an important impact on the atmospheric environment and ecosystem security.

[0003] Currently, N2O emissions and NH3 volatilization are often measured separately using different culture systems or experimental setups. For example, N2O emissions are typically measured in a closed culture system using headspace gas collection, while NH3 volatilization is often measured in an independent system using acid absorption or a ventilation system. These separate system or time-scale measurement methods make it difficult to ensure consistency in culture conditions, microbial activity, and time scales between the two gaseous nitrogen measurement processes, resulting in poor comparability of the measurement results.

[0004] N2O emissions and NH3 volatilization may exhibit an inverse or synergistic relationship. Measuring only one type of gaseous nitrogen may overestimate or underestimate the regulatory effect on gaseous nitrogen loss, making it difficult to accurately assess its true environmental impact. Therefore, there is an urgent need for a method or apparatus that can simultaneously measure N2O emissions and NH3 volatilization within the same culture system and on the same timescale, in order to achieve a comprehensive and accurate assessment of the environmental effects. Summary of the Invention

[0005] The purpose of this invention is to provide a method for simultaneously measuring soil N2O emissions and NH3 volatilization, enabling the coordinated measurement of multiple nitrogen process parameters on the same time scale, thereby solving the problems of asynchronous gaseous nitrogen measurement, inconsistent culture conditions, and mutual interference between processes in the prior art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for simultaneously determining soil N2O emissions and NH3 volatilization involves first aerobically culturing soil samples, followed by a 24-hour sealed treatment, and then simultaneously measuring N2O and NH3 concentrations under the same culture system conditions.

[0007] Furthermore, soil samples were aerobically cultured in the same culture container and then sealed for 24 hours. During the sealing period, N2O was accumulated and NH3 was absorbed simultaneously. The above aerobic culture-aerobic culture operation was repeated periodically. After each sealing cycle, the N2O concentration and NH3 concentration were measured simultaneously.

[0008] The culture container is equipped with a headspace gas collection device at the top to collect N2O generated during the culture process; the culture container is equipped with an acid absorption unit inside to absorb NH3 volatilized during the culture process.

[0009] The acid absorption unit is a porous sponge impregnated with dilute sulfuric acid.

[0010] The gas collection of N2O and the absorption of NH3 are completed within the same closed cycle to ensure the consistency of the measurement results of the two gaseous nitrogen states over the same time scale.

[0011] The gas collection device injects N2O into a vacuum gas collection bottle, and the N2O concentration is determined using a gas chromatograph.

[0012] The porous adsorbent material was immersed in KCl solution and extracted by shaking. NH4 was then determined. + The -N content is used to calculate the NH3 concentration.

[0013] A method for determining the N2O emission rate and NH3 volatilization rate in soil, wherein the N2O concentration and NH3 concentration are determined by the method, the N2O emission rate is calculated by formula (1), and the NH3 volatilization rate is calculated by formula (2); Formula for calculating the emission rate of gaseous N2O: F=ρ× × × × ×24 (1) Where: F is the N2O emission rate, mg·kg -1 ·d -1 ρ is the density of N₂O; V is the effective volume of the culture flask, in m³. 3 W represents the dry soil weight of the culture bottle, kg; dc / dt represents the gas concentration change between two adjacent sampling intervals, ppm; T represents the temperature during incubation, 25℃; Δt represents the gas sampling interval, h. Formula for calculating the NH3 volatilization rate in soil: (2) In the formula, Fr is the NH3 volatilization rate, kg·hm -2 ·d -1 ; C NH4 + -N concentration, mg·L -1 ; V The volume of the extract is in ml.

[0014] The present invention has the following beneficial effects: The method of this invention involves aerobic soil culture under the same culture conditions. By setting a headspace gas collection structure at the top of the culture container and an acidic absorption unit inside the container, spatial separation and collection of N2O and NH3 are achieved. Furthermore, through periodic closed-system culture operations, the two gaseous nitrogen species are simultaneously measured within the same culture timescale. Specifically: (1) Realize simultaneous monitoring of multiple gaseous nitrogen states This invention enables the simultaneous measurement of N2O emissions and NH3 volatilization within the same culture system and the same culture cycle, avoiding the time asynchrony problem caused by traditional separate system or time-segmented measurement methods, and providing a unified technical means for the collaborative study of multiple gaseous nitrogen loss processes.

[0015] (2) Ensure consistency of culture conditions and improve data comparability Since the determination of N2O and NH3 both come from the same culture conditions and the same soil samples, the culture conditions, microbial activity and nitrogen transformation stages are kept consistent, which effectively eliminates the systematic errors introduced by the spatial heterogeneity of soil and the differences in culture conditions, and improves the comparability between the determination results of different gaseous nitrogen.

[0016] (3) Improve the accuracy of environmental impact assessment By simultaneously acquiring N2O emissions and NH3 volatilization data, this invention can more accurately reflect the comprehensive regulatory effect of different gaseous nitrogen loss pathways, avoiding misjudgments due to measuring only one type of gaseous nitrogen, thereby improving the accuracy and reliability of environmental effect assessment.

[0017] (4) The method is highly versatile and easy to operate. This invention is a methodological solution that is independent of soil type. While ensuring the effectiveness of simultaneous measurement, it maintains good operability and repeatability, and has good prospects for widespread application. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the culture system structure and sampling flowchart for the simultaneous determination of N2O and NH3 in Example 1 of the present invention; Figure 2 This is a graph showing the N2O emission and NH3 volatilization rate during the cultivation period in Example 1 of the present invention. Detailed Implementation

[0019] The present invention will be further described below with reference to specific embodiments. These embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Equivalent substitutions or adjustments made by those skilled in the art to the implementation conditions, steps, or parameters without departing from the technical concept of the present invention should all fall within the scope of protection of the present invention.

[0020] This invention achieves spatial separation of two gaseous nitrogen collection methods within the same culture container by rationally setting up a headspace gas collection structure and an NH3 acidic absorption unit. Simultaneously, in conjunction with periodic closed aeration culture operations, the accumulation of N2O and the absorption of NH3 are carried out synchronously within the same culture system and the same culture time scale, thereby constructing a stable and non-interfering synchronous measurement system.

[0021] This invention enables the simultaneous and independent determination of N2O and NH3 without significantly increasing experimental complexity, and is suitable for indoor incubation studies of soil nitrogen cycling processes.

[0022] Example 1 In this embodiment, each step of the operation must ensure that the solution is added evenly and the soil moisture is controlled stably; the sealing and aeration conditions must be strictly controlled before and after gas sampling to ensure the consistency of the cultivation conditions; the NH3 absorption unit should cover the NH3 volatilization path to avoid external interference.

[0023] 1. Experimental Materials 1.1 Test Soil In this embodiment, topsoil from farmland was selected as the culture medium. The soil was alluvial soil (yellow alluvial soil subclass), collected from the Agricultural Ecological Experimental Station of Fengqiu City, Henan Province (114°24′E, 35°00′N). Soil from the 0-20 cm topsoil layer was collected, and after removing visible plant debris and stones, it was sieved through a 2 mm sieve, mixed thoroughly, and stored at 4 ℃ for later use. The basic physicochemical properties of the soil are as follows: pH 8.2, organic carbon content 12.5 g·kg⁻¹. -1 The total nitrogen content is 0.94 g·kg⁻¹. -1 The soil is silty loam, with sand, silt and clay accounting for 69%, 27% and 4% respectively.

[0024] 1.2 Main Reagents The nitrogen fertilizer used is urea (analytical grade, Tianjin Damao Chemical Reagent Factory, China).

[0025] 2. Experimental treatment settings This embodiment sets up a soil culture system, which is repeated 3 times, to verify the effect of the simultaneous measurement method of the present invention on the simultaneous measurement of soil N2O emissions and NH3 volatilization.

[0026] 3. Sample Preparation 3.1 Soil Preparation Weigh 20 g (by dry weight) of soil sample and place it in a 250 mL Erlenmeyer flask. Gently shake to distribute the soil evenly. Pre-incubate at 25 ℃ for 2 days to restore soil microbial activity.

[0027] 3.2 Solution Preparation Prepare a urea solution.

[0028] 3.3 Moisture Regulation The soil moisture content was adjusted to about 60% of the maximum water holding capacity using deionized water, and water was replenished regularly during the cultivation process to maintain stable soil moisture.

[0029] 4. Culture container See culture container Figure 1 A headspace gas collection device is installed at the top of the conical flask to collect N2O generated during the culture process; a porous sponge soaked in dilute sulfuric acid is installed at the neck of the conical flask to absorb NH3 volatilized during the culture process.

[0030] 5. Culture and simultaneous measurement After the pre-culture is completed, add 2 mL of urea solution evenly to each conical flask. The amount of urea added to the solution should be based on the final nitrogen application rate of 100 mg N·kg. -1 Soil preparation. The conical flasks were sealed with sealing film, and holes were punched in the sealing film to ensure gas exchange during incubation. Aerobic incubation was carried out under constant temperature conditions of 25±1 ℃.

[0031] Before gas sampling, the culture system was sealed for 24 hours to accumulate N2O. During sampling, headspace gas was repeatedly extracted from the culture flask using a syringe and mixed thoroughly. A quantitative gas sample was injected into a vacuum sampling bottle, and the N2O concentration was determined using a gas chromatograph. The absorbing sponge was then removed and immersed in 100 mL of KCl solution for extraction. The extract was used to determine NH4+. + The N₂O content was used to calculate the NH₃ concentration. According to the formula described in this invention, the N₂O concentration in the headspace gas on day 2 of cultivation was 0.34 mg·L⁻¹. -1 NH4 in the absorption liquid + -N concentration was 0.40 mg·L⁻¹ -1 On day 10 of culture, the concentrations were 0.02 mg·L⁻¹. -1 and 0.12 mg·L -1 On day 30 of culture, the concentration was 0.01 mg·L⁻¹. -1 and 0.08 mg·L -1 .

[0032] After sampling, the culture system was briefly aerated, and culture continued after restoring aerobic conditions. The above aerobic culture-aerobic culture operation was repeated periodically, and the N2O and NH3 concentrations were measured simultaneously at the end of each closed cycle. Figure 2 This indicates that the N2O emission rate increases rapidly in the early stages of cultivation, reaching a peak of 106.41 μg·kg on the second day of cultivation. -1 ·d -1The nitrogen emission rate initially decreased gradually and then stabilized in the later stages of cultivation. Similarly, the NH3 volatilization rate was high in the early stages of cultivation, then gradually decreased, and remained at a low level in the later stages. These results demonstrate that the synchronous measurement system established in this invention can simultaneously acquire N2O emission and NH3 volatilization data under the same cultivation conditions, achieving simultaneous monitoring of the two gaseous nitrogen loss processes.

[0033] 6. Soil nitrogen transformation rate 6.1 Calculation of N2O emission rate In this embodiment, the N2O emission rate is calculated based on the change of N2O concentration in the culture system over time, and can be expressed by the following formula: Formula for calculating the emission rate of gaseous N2O: F=ρ× × × × ×24 In the formula: F is the N2O production rate, mg·kg -1 ·d -1 ρ is the density of N2O under standard conditions; V is the effective volume of the culture flask, in m³. 3 W represents the dry soil weight of the culture bottle, kg; dc / dt represents the gas concentration change between two adjacent sampling intervals, ppm; T represents the temperature during cultivation, 25 ℃; Δt represents the gas sampling interval, h, 24 is used for unit conversion.

[0034] In this embodiment: Day 2 of training

[0035] Take: ρ = 1.25 kg·m -3 V=0.00020 m 3 Given W = 0.020 kg, T = 25 ℃, Δt = 24 h, and dc / dt = 32.8 ppm, substituting these values, we get: Day 10 of cultivation Substituting the values, we get: 0.76 μg·kg -1 ·d -1 Day 30 of cultivation Substituting the values, we get: 0.12 μg·kg -1 ·d -1 ; In this embodiment, the soil N2O emission rate under different treatments peaked in the early stage of cultivation, then rapidly decreased and tended to stabilize. Taking day 1 of cultivation as an example, the N2O emission rate was 85.69 μg·kg⁻¹. -1 ·d -1The N2O emission rate peaked on day 2 of cultivation, with a rate of 106.41 μg·kg⁻¹. -1 ·d -1 In the later stages of cultivation (after day 10), the N2O emission rate decreased to 1 μg·kg⁻¹. -1 ·d -1 the following.

[0036] 6.2 Calculation of NH3 volatilization rate The evaporation rate of NH3 depends on the amount of NH4 in the absorbent. + The -N content can be calculated using the following formula: Formula for calculating the NH3 volatilization rate in soil:

[0037] In the formula, Fr is the NH3 volatilization rate, kg·hm -2 ·d -1 ; C NH4 in sponge extract + -N concentration, mg·L -1 ; V The value represents the volume of the extract in ml, and the other parameters are conversion coefficients.

[0038] In this embodiment: Day 2 of training

[0039] Where: C = 0.26 mg·L -1 V = 40 mL, substitute into: Day 10 of cultivation Substituting the values, we get: 0.0067 kg·hm -2 ·d -1 Day 30 of cultivation Substituting the values, we get: 0.0042 kg·hm -2 ·d -1 In this embodiment, the NH3 volatilization rate was also high in the early stage of cultivation, and then gradually decreased. Taking day 1 of cultivation as an example, the NH3 volatilization rate was 0.0342 kg·hm². -2 ·d -1 On day 2 of cultivation, the NH3 volatilization rate decreased to 0.0218 kg·hm². -2 ·d -1 After 10 days of cultivation, the NH3 volatilization rate decreased to 0.01 kg·hm². -2 ·d -1 the following.

Claims

1. A method for simultaneously determining soil N2O emissions and NH3 volatilization, characterized in that, Soil samples were first cultured aerobically, then sealed for 24 hours. Under the same culture system conditions, the concentrations of N2O and NH3 were measured simultaneously.

2. The method for simultaneously determining soil N2O emissions and NH3 volatilization according to claim 1, characterized in that, Soil samples were aerobically cultured in the same culture container and then sealed for 24 hours. During the sealing period, N2O was accumulated and NH3 was absorbed simultaneously. The above aerobic culture-aerobic culture operation was repeated periodically. After each sealing cycle, the N2O concentration and NH3 concentration were measured simultaneously.

3. The method for simultaneously determining soil N2O emissions and NH3 volatilization according to claim 1, characterized in that, The culture container is equipped with a headspace gas collection device at the top to collect N2O generated during the culture process; the culture container is equipped with an acid absorption unit inside to absorb NH3 volatilized during the culture process.

4. The method for simultaneously determining soil N2O emissions and NH3 volatilization according to claim 3, characterized in that, The acid absorption unit is a porous sponge impregnated with dilute sulfuric acid.

5. The method for simultaneously determining soil N2O emissions and NH3 volatilization according to claim 3, characterized in that, The gas collection of N2O and the absorption of NH3 are completed within the same closed cycle to ensure the consistency of the measurement results of the two gaseous nitrogen states over the same time scale.

6. The method for simultaneously determining soil N2O emissions and NH3 volatilization according to claim 3, characterized in that, The gas collection device injects N2O into a vacuum gas collection bottle, and the N2O concentration is determined using a gas chromatograph.

7. The method for simultaneously determining soil N2O emissions and NH3 volatilization according to claim 3, characterized in that, The porous adsorbent material was immersed in KCl solution and extracted by shaking. NH4 was then determined. + The -N content is used to calculate the NH3 concentration.

8. A method for determining soil N2O emission rate and NH3 volatilization rate, characterized in that: The N2O concentration and NH3 concentration were determined by the method described in claim 1. The N2O emission rate was calculated by formula (1), and the NH3 volatilization rate was calculated by formula (2). Formula for calculating the emission rate of gaseous N2O: F=ρ× × × × ×24 (1) Where: F is the N2O emission rate, mg·kg -1 ·d -1 ρ is the density of N₂O; V is the effective volume of the culture flask, in m³. 3 W represents the dry soil weight of the culture bottle, kg; dc / dt represents the gas concentration change between two adjacent sampling intervals, ppm; T represents the temperature during incubation, 25℃; Δt represents the gas sampling interval, h. Formula for calculating the NH3 volatilization rate in soil: （2） In the formula, Fr is the NH3 volatilization rate, kg·hm -2 ·d -1 ; C NH4 + -N concentration, mg·L -1 ; V The volume of the extract is in ml.

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