An effective method for estimating soil nitrate assimilation rate

Abstract

The present invention discloses a method for effectively estimating the soil nitrate nitrogen assimilation rate, which comprises the following steps: (1) obtaining the physicochemical properties of organic matter; (2) obtaining the nitrate nitrogen assimilation rate of soil nitrate nitrogen; 15 Organic nitrogen using N tracer technology 15 The N recovery method calculates the soil nitrate nitrogen assimilation rate under the input of organic materials; (3) the data of step (1) and step (2) are input into SIMCA software, and the importance of the physical and chemical properties of organic materials to the soil nitrate nitrogen assimilation rate is evaluated using projection importance analysis to obtain a VIP diagram; (4) the physical and chemical properties of organic materials that best affect the soil nitrate nitrogen assimilation rate are determined based on the VIP diagram, and a regression equation is established. The present invention uses laboratory analysis and regression model establishment methods to quickly and effectively estimate the soil nitrate nitrogen assimilation rate, which can overcome the cumbersome field operations and technical deficiencies, and no longer requires the addition of organic materials in the subsequent evaluation of the soil nitrate nitrogen assimilation capacity under the input of organic materials. 15 N markers, save costs, and thus have good promotion and practical significance.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation, and in particular to a method for effectively estimating the soil nitrate nitrogen assimilation rate. Background Art

[0002] Excessive nitrogen fertilizer application and rainfall or irrigation cause nitrate accumulation in farmland soils. This accumulated nitrate is easily lost through leaching, runoff, and denitrification, leading to ecological problems such as soil quality degradation, water pollution, and emissions of the greenhouse gas nitrous oxide (NO) (Yang et al., 2020; Gao et al., 2021). Soil nitrate assimilation involves the conversion of nitrate into microbial biomass nitrogen through a series of biochemical reactions by soil microorganisms, thereby reducing nitrate accumulation and potentially playing an important role in addressing the current problem of soil nitrate accumulation (Qiu et al., 2013; Wang et al., 2021). However, due to land use patterns, farmland soil organic carbon content and quality are significantly lower than those in forest and grassland soils, limiting microbial utilization of nitrate (Zhang et al., 2013; Li et al., 2019). However, a meta-analysis found that when a readily degradable carbon source, such as glucose, is added at an input exceeding 500 mg kg, the soil organic carbon content and quality are significantly lower than those in forest and grassland soils, limiting microbial utilization of nitrate (Zhang et al., 2013; Li et al., 2019). -1 When the carbon (C) / N ratio of plant residues is greater than 18, they can significantly enhance the soil nitrate assimilation process (Cheng et al., 2017).

[0003] Traditionally, it is usually used 15 N isotope dilution method, organic nitrogen 15 N recovery and microbial biomass nitrogen 15 The N recovery method calculates the soil nitrate nitrogen assimilation rate, while the above three methods require the addition of 15 The use of nitrogen markers makes calculating nitrate assimilation rates expensive (Burger and Jackson, 2003; Chen et al., 2019). Furthermore, the numerous measurement parameters make the entire process cumbersome. To quickly and conveniently determine soil nitrate assimilation rates in response to organic material inputs, a method for effectively estimating soil nitrate assimilation rates is urgently needed. This would facilitate rapid identification of the optimal organic carbon source, reduce nitrate accumulation in farmland soils, and mitigate associated environmental risks. Summary of the Invention

[0004] Purpose of the invention: The present invention aims to provide a method for effectively estimating the soil nitrate nitrogen assimilation rate.

[0005] Technical solution: The method for effectively estimating the soil nitrate nitrogen assimilation rate of the present invention comprises the following steps:

[0006] (1) Obtain the physical and chemical properties of organic materials;

[0007] (2) Obtaining 15 Organic nitrogen using N tracer technology 15 The N recovery method was used to calculate the soil nitrate assimilation rate under the input of organic matter;

[0008] (3) Inputting the data obtained in steps (1) and (2) into SIMCA software, using projection importance analysis to evaluate the importance of the physical and chemical properties of organic materials on the soil nitrate nitrogen assimilation rate, and obtaining a VIP map;

[0009] (4) Based on the VIP diagram, the physical and chemical properties of organic materials that best affect the soil nitrate nitrogen assimilation rate are determined, and then regression analysis is used to establish a regression equation.

[0010] Furthermore, in step (1), the organic material is five or more of wheat leaves, corn leaves, rice bran, peanut straw, rice leaves, rice husks, corn stalks, sodium lignin sulfonate, cellulose, sodium acetate, glucose, sawdust, or molasses powder; the physical and chemical properties include pH, total nitrogen, C / N ratio, lignin, holocellulose, soluble organic carbon, soluble organic nitrogen, lignin / nitrogen ratio, holocellulose / nitrogen ratio, soluble organic carbon / soluble organic nitrogen ratio, and organic material carbon mineralization rate. Furthermore, in step (2), the soil is nitrate-contaminated soil from an arid, semi-arid, or semi-humid region; the organic material is pulverized and passed through a 40-100 mesh sieve.

[0011] Furthermore, the method further comprises: step (5) verifying the regression equation by the physical and chemical properties of other organic materials and the soil nitrate nitrogen assimilation rate under the input of organic materials measured in step (2).

[0012] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0013] (1) The present invention can estimate the soil nitrate nitrogen assimilation rate under different types of organic material input through simple measurement, overcoming the cumbersome field operation and technical deficiencies;

[0014] (2) The present invention can make it possible to avoid adding 15 N marker, estimated cost is lower;

[0015] (3) The present invention can not only estimate the soil nitrate nitrogen assimilation rate, which is conducive to quickly finding the best organic material, but also reflect the microbial activity status of the soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a variable projection importance analysis (VIP value) diagram of soil nitrate nitrogen assimilation rate and plant residue properties in different organic material treatments in Example 1 of the present invention;

[0017] Figure 2 : is a regression relationship diagram of the organic material carbon mineralization rate and the soil nitrate nitrogen assimilation rate in Example 1 of the present invention;

[0018] Figure 3 Graph showing the regression relationship between the carbon mineralization rate of organic matter and the nitrate nitrogen assimilation rate in soil in Examples 1 and 2 of the present invention. DETAILED DESCRIPTION

[0019] The technical solution of the present invention will be further described below in conjunction with the embodiments and drawings.

[0020] Example 1: The method for effectively estimating the soil nitrate nitrogen assimilation rate according to the present invention comprises the following steps:

[0021] (1) Obtain the physicochemical properties of organic materials: pH, total nitrogen, C / N ratio, lignin, holocellulose, soluble organic carbon, soluble organic nitrogen, lignin / nitrogen ratio, holocellulose / nitrogen ratio, soluble organic carbon / soluble organic nitrogen ratio, and carbon mineralization rate of organic materials;

[0022] (2) Obtaining 15 Organic nitrogen using N tracer technology 15 The N recovery method calculates the soil nitrate nitrogen assimilation rate under the input of organic matter, specifically:

[0023] (3) Soil sample 1 was collected from the field, and impurities such as plant roots and stones were removed. After passing through a 10-mesh sieve (2 mm), it was stored in a refrigerator at 4 °C for cultivation experiments. The soil sample was collected from the nitrate-contaminated soil around the Fengqiu Agricultural Ecological Experimental Station of the Chinese Academy of Sciences in 2019.

[0024] (4) Weigh several 20 g (dry soil weight) soils and place them in 250 mL conical flasks and incubate them in a 25°C constant temperature incubator for one day;

[0025] (5) After incubation, wheat leaves, corn leaves, rice bran, peanut straw, rice leaves, rice husks, corn stalks, sodium lignin sulfonate, cellulose, sodium acetate, and glucose were added to the soil samples at a rate of 5 g C kg -1, and set the treatment without adding organic materials. Among them, wheat leaves, corn leaves, rice bran, peanut straw, rice leaves, rice husks, corn stalks, and cellulose were crushed by a Deke laboratory grinder, passed through a 60-mesh sieve (250μm), and added in powder form. Other organic materials were mixed with the nitrate nitrogen solution marked in the next step and added;

[0026] (6) Add 2 mL of 15 The soil samples were then incubated in a 25°C constant temperature incubator for 12 consecutive days. During the incubation period, the bottles were aerated for 30 minutes every two days to ensure sufficient oxygen in the bottles, and water lost due to evaporation was replenished by weighing. The water conditions simulated the general field water conditions in arid, semi-arid, and semi-humid regions.

[0027] (7) On the 0.02, 1, 3, 6 and 12th day after incubation, three soil samples were randomly taken from each organic material treatment and the treatment without organic material addition to determine the soil nitrate nitrogen and insoluble organic nitrogen content and other 15 Nitrate abundance was measured. The soil CO2 emission rate was also measured, except for 0.02 days. The number of incubation days was determined based on the release time of active organic carbon from plant residues, which is generally within 2 weeks (Blagodatskaya et al., 2009; Zheng and Marschner, 2017). Nitrate concentration was extracted with 2M potassium chloride solution at a ratio of 1:5 and then measured using a flow analyzer. 15 Before measuring the nitrogen abundance, the extract must be treated by diffusion method. First, magnesium oxide is used to convert ammonium nitrogen into NH3 for removal. Then Dai's alloy is added to convert nitrate nitrogen into NH3, and oxalic acid is used to absorb it. Then, the nitrate nitrogen is dried and measured. 15 N abundance: The extracted soil was filtered 2-3 times with qualitative filter paper to remove inorganic nitrogen concentration in the soil, then placed in an oven at <60°C for drying, ground, passed through a 100-mesh sieve (150 μm), and packaged. The soil insoluble organic nitrogen content and other nitrogen were then determined using a stable isotope mass spectrometer (IRMS 20-22, SerCon, Crewe, UK). 15 N abundance;

[0028] (8) Before collecting gas samples, all samples were ventilated. That is, the gas in the bottle was repeatedly flushed with fresh air three times to ensure that there was no residual CO2 generated by the soil in the gas space inside the culture bottle. At the same time, 40 mL of air was collected from the air inlet of the ventilation device as a blank and injected into a 22.5 mL vacuum bottle as the initial gas. After the culture bottle was sealed with a stopper for 6 hours, the gas in the culture bottle was collected with a 50 mL syringe and transferred to a vacuum cylinder for measuring the CO2 concentration.

[0029] (9) Utilization of organic nitrogen 15 Calculation of soil nitrate assimilation rate (I NO3 ), the formula is:

[0030] Org 15 N i =OrgN i ×Ae OrgNi

[0031]

[0032] Where: i is the i-th sampling; Org 15 N i is the soil insoluble organic nitrogen at the time of sampling 15 N concentration;OrgN i is the soil insoluble organic nitrogen concentration at the time of sampling; Ae OrgNi is the soil insoluble organic nitrogen at the time of sampling 15 N abundance; Ae i is the nitrate nitrogen at the time of sampling 15 N abundance; n is the number of sampling times; d is the number of culture days; the CO2 emission rate of all treatments was calculated using the gas emission formula, which is as follows:

[0033]

[0034] Where: F is the CO2 production rate (mg kg -1 d -1 ), ρ is the gas density under standard conditions (0.54 kg CO2-C m -3 ), V is the effective volume of the culture flask (m 3 ), W is the dry weight of the incubated soil (kg), dc / dt represents the change in gas concentration between two consecutive sampling times (ppm), T is the incubation temperature (25°C), Δt is the gas sampling interval (h), and 24 is used for unit conversion. Furthermore, the organic material carbon mineralization rate is the difference between the CO₂ emission rate of the soil treated with the corresponding organic material and the CO₂ rate of the soil treated without organic material.

[0035] (10) The data obtained in steps (1) and (2) (see Table 1) were input into SIMCA software, and the importance of the physical and chemical properties of organic materials on the soil nitrate nitrogen assimilation rate was evaluated using projection importance analysis to obtain a VIP diagram;

[0036] (11) According to the VIP diagram, the physical and chemical properties of organic materials that best affect the soil nitrate nitrogen assimilation rate are determined, such as Figure 1As shown in the results, it was shown that only the carbon mineralization rate of organic matter was the key organic matter property that affected the soil nitrate nitrogen assimilation rate. Then, regression analysis was used to establish a quantitative relationship between the carbon mineralization rate of organic matter and the nitrate nitrogen assimilation rate, as shown in the following figure: Figure 2 As shown, the relationship is: y = 0.02x + 0.81.

[0037] Table 1 Soil nitrate assimilation rate and organic material carbon mineralization rate under various organic material treatments

[0038]

[0039] Example 2: The difference from Example 1 is that: in step (1), the organic materials are corn leaves, rice bran, rice husks, wheat straw and glucose; in step (2), the soil is nitrate-contaminated soil collected from the vicinity of the Fengqiu Agricultural Ecological Experimental Station of the Chinese Academy of Sciences in 2021.

[0040] The organic material carbon mineralization rate and the corresponding nitrate nitrogen assimilation rate were calculated (Table 2). The data were input into the regression model, and the coefficients were corrected to obtain the final regression relationship: y = 0.03x + 0.60.

[0041] Example 2 also includes step (5) of verifying the regression equation using the physical and chemical properties of sawdust and molasses powder and the soil nitrate nitrogen assimilation rate under organic material input measured in step (2). As shown in Table 3, after adding sawdust, the soil nitrate nitrogen assimilation rate simulated based on the organic material carbon mineralization rate was 33.75% lower than the actual nitrate nitrogen assimilation rate; after adding molasses powder, the soil nitrate nitrogen assimilation rate simulated based on the organic material carbon mineralization rate was 17.40% lower than the actual nitrate nitrogen assimilation rate. The above results indicate that measuring the organic material carbon mineralization rate under organic material input can better predict the soil nitrate nitrogen assimilation rate. At the same time, the organic material carbon mineralization rate also reflects the metabolic status of microorganisms in the soil. Molasses powder, as a by-product of the sugar processing plant, is more easily utilized by microorganisms than sawdust. Therefore, the molasses powder carbon mineralization rate is higher than the sawdust carbon mineralization rate, and the microbial activity is higher under this treatment. The proposed method helps to quickly determine the type of organic material that best improves the soil nitrate nitrogen assimilation rate, thereby providing theoretical and technical support for alleviating the environmental risk of nitrate nitrogen accumulation in farmland soil.

[0042] Table 2 Soil nitrate assimilation rate and organic matter carbon mineralization rate under different organic matter treatments

[0043]

[0044] Table 3 Carbon mineralization rates after sawdust and molasses powder addition and simulated and measured soil nitrate assimilation rates under the corresponding treatments

[0045]

Claims

1. A method for effectively estimating the soil nitrate nitrogen assimilation rate, characterized in that: The following steps are involved: (1) Determine the organic carbon mineralization rate of organic materials; (2) Substituting the measured organic matter carbon mineralization rate into a predetermined linear regression equation to directly calculate the soil nitrate nitrogen assimilation rate; wherein the linear regression equation is established by the following method: (a) Select at least five different organic materials and measure their carbon mineralization rate, pH, total nitrogen, C / N ratio, lignin, holocellulose, soluble organic carbon, soluble organic nitrogen, lignin / nitrogen ratio, holocellulose / nitrogen ratio, and soluble organic carbon / soluble organic nitrogen ratio; (b) Adoption 15 The nitrate nitrogen assimilation rate of soil after adding various organic materials was determined by N tracing technology; the soil was nitrate-contaminated soil in arid, semi-arid or semi-humid areas; the amount of organic material added was 5 g C kg -1 ; (c) Projection importance analysis was performed using SIMCA software to confirm that the carbon mineralization rate of organic materials was the key indicator for the maximum VIP value; (d) Establish a quantitative relationship model between the carbon mineralization rate of organic matter and the nitrate nitrogen assimilation rate.

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