A method for determining lime requirements for improving acidic soil under field conditions

Abstract

The present invention provides a method for determining the amount of lime required for improving acidic soil under field conditions, belonging to the technical field of acidic soil improvement. The present invention uses a primary equilibrium method to extract active aluminum from acidic soil, then performs complex color development with a chrome azurol S mixed colorant and active aluminum, and uses the RGB method to determine the aluminum concentration and active aluminum content in the active aluminum test solution. Finally, the acid neutralization capacity (ANC) of the lime and the active aluminum content (Al) are determined. act The lime requirement LR is calculated based on the molar ratio of [OH] / [Al] of soil active aluminum. The present invention provides a feasible method for determining soil active aluminum under field conditions, solving the time-consuming and labor-intensive problem of determining lime requirements when improving acidic soils, and significantly improving the efficiency of diagnosis and decision-making for acidic soil improvement.

Description

Technical Field

[0001] The invention relates to the technical field of acidic soil improvement, and in particular to a method for determining lime requirement for improving acidic soil under field conditions. Background Art

[0002] Acidic soil solutions typically contain high concentrations of aluminum, while other nutrients such as calcium, magnesium, and phosphorus are low. Aluminum toxicity to crop roots has long been a major factor limiting crop growth in acidic soils. Soil acidity can be addressed through the application of lime, a calcium-rich base that neutralizes soil acidity and raises soil pH. Lime requirement generally refers to the amount of lime needed to achieve a target soil pH or active aluminum content. The amount of lime added should be sufficient to neutralize soil acidity and eliminate the toxicity of active soil aluminum to crops. The amount of lime required to adjust soil acidity generally depends on the initial soil pH, the soil's acid-base buffering capacity, the target pH, and the acid-neutralizing capacity of the lime material. Currently, lime requirement is typically determined by taking soil samples collected in the field and returning them to the laboratory through a series of simulation studies. For example, soil pH buffering capacity is measured in the laboratory, and the lime requirement is calculated based on parameters such as the difference between the target and initial soil pH, soil bulk density, and the acid-neutralizing capacity of the lime. However, measuring soil pH buffering capacity, one of the aforementioned parameters, is time-consuming, requiring seven days or more. This step also complicates the determination of lime requirements, and this method can only be performed in the laboratory. Therefore, using this method to diagnose and make decisions about acidic soil improvement is time-consuming and labor-intensive, and it fails to provide farmers with timely guidance on soil improvement based on field conditions. To address this technical issue, developing a method for estimating the amount of lime required for acidic soil improvement under field conditions would provide rapid and timely guidance for acidic soil improvement, which would be of great practical significance.

[0003] Based on research on soil aluminum chemistry, a method for estimating the lime requirement for acidic soil improvement by eliminating the toxic effects of active aluminum in acidic soils has been proposed. Active aluminum in acidic soils primarily consists of exchangeable aluminum and soluble aluminum. Accurately and rapidly determining the active aluminum content in acidic soils under field conditions is a key step in this method. Currently, laboratory extraction of active aluminum, such as exchangeable aluminum, from soils typically involves multiple leaching with a 1 mol / L potassium chloride solution. Following extraction, aluminum content is determined using alkaline titration, UV-visible spectrophotometry, atomic absorption spectrometry, or inductively coupled plasma optical emission spectrometry. Multiple leaching methods are time-consuming and labor-intensive to extract active aluminum, making them difficult to implement in the field. Determination of aluminum content using methods such as UV-visible spectrophotometry, atomic absorption spectrometry, and inductively coupled plasma optical emission spectrometry requires large instrumentation, confining it to the laboratory and making it difficult to implement in the field. Furthermore, the precision instruments used in atomic absorption spectrometry and inductively coupled plasma optical emission spectrometry are expensive, bulky, and difficult to carry. The measurement process is cumbersome and requires specialized analysis, resulting in a long wait for experimental results. It can be seen that there is a lack of a reliable and easy-to-operate method for determining the active aluminum content in soil under field conditions. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for determining the amount of lime required for improving acidic soil under field conditions, so as to solve the problem in the prior art that the determination of soil pH buffer capacity is time-consuming and difficult to implement under field conditions, resulting in the inability to quickly diagnose and decide on the improvement of acidic soil and the inability to carry out the improvement in a timely manner.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for determining the amount of lime required for improving acidic soil under field conditions, comprising the following steps:

[0007] (1) Adding the soil sample to a potassium chloride solution, shaking it manually, letting it stand, and filtering it to obtain an active aluminum extract;

[0008] (2) mixing the active aluminum extract, the mixed color developer, the masking agent, and the pH buffer solution to obtain an active aluminum color developer solution, then preparing an aluminum standard solution color developer solution, measuring the color difference ΔE of the aluminum standard solution, and establishing a standard curve of aluminum concentration and color difference ΔE;

[0009] (3) Determine the color difference of the active aluminum test solution and calculate the aluminum concentration [mmol / L] in the active aluminum extract and the active aluminum content [Al] in the soil according to the standard curve. act (mmol / kg);

[0010] (4) If the active aluminum content [Al] act>2.00mmol / kg, it is determined that the soil needs to be improved, otherwise no improvement is needed;

[0011] (5) Mix lime and water, and titrate the resulting mixed suspension with hydrochloric acid solution to a pH of 5.5-6.0. Record the consumption of hydrochloric acid solution V, and calculate the acid neutralization capacity ANC of the lime according to formula (1):

[0012]

[0013] Wherein, V is the consumption of hydrochloric acid solution, in mL;

[0014] C is the concentration of hydrochloric acid solution, in mol / L;

[0015] m is the mass of lime, in g;

[0016] ANC is the acid neutralization capacity of lime, in mol / kg;

[0017] (6) After mixing the soil sample with water, measure the pH value of the soil and calculate the molar ratio of active aluminum in the soil [OH] / [Al] according to formula (2):

[0018]

[0019] (7) Calculate the lime requirement LR for improving acidic soil according to formula (3):

[0020]

[0021] Where ρ is the soil bulk density in g / cm 3 ;

[0022] [Al] act is the active aluminum content in the soil, in mmol / kg;

[0023] [Al] is the concentration of aluminum, in [mmol / L];

[0024] LR is the lime requirement in kg / ha.

[0025] Preferably, in step (1), the mass volume ratio of the soil sample to the potassium chloride solution is 1-3 g: 20-30 mL, wherein the concentration of the potassium chloride solution is 0.5-1.5 mol / L.

[0026] Preferably, in the step (1), the manual shaking time is 1 to 3 minutes; and the standing time is 20 to 40 minutes.

[0027] Preferably, in step (2), the mixed developer is prepared by mixing a chrome azurol S solution and a cetyltrimethylammonium bromide solution to obtain a mixed developer.

[0028] Preferably, the chrome azure blue S solution is prepared by mixing chrome azure blue S and water, wherein the mass volume ratio of chrome azure blue S to water is 1 g:400-600 mL; the cetyltrimethylammonium bromide solution is prepared by mixing cetyltrimethylammonium bromide and ethanol, wherein the mass volume ratio of cetyltrimethylammonium bromide to ethanol is 1 g:40-60 mL; the volume ratio of the chrome azure blue S solution to the cetyltrimethylammonium bromide solution is 40-60:4-6.

[0029] Preferably, in step (5), the mass volume ratio of lime to water is 1 g: 300-500 mL.

[0030] Preferably, in step (5), the concentration of the hydrochloric acid solution is 0.8 to 1.2 mol / L.

[0031] Preferably, in step (6), the mass ratio of the soil sample to water is 1:2-3.

[0032] Beneficial effects of the present invention:

[0033] (1) The present invention can determine the active aluminum content in acidic soil under field conditions, and then calculate the amount of lime required for improving the acidic soil based on the active aluminum content. Compared with the traditional method of determining the soil pH buffering capacity under laboratory conditions and then calculating the amount of lime required, the method provided by the present invention is faster and simpler for estimating the amount of lime required for improving acidic soil.

[0034] (2) The present invention adopts a single equilibrium method to extract active aluminum from acidic soil. Compared with the laboratory method of extracting active aluminum from soil by multiple leaching with potassium chloride solution, it saves time and labor and is convenient for field operation.

[0035] (3) Since the active aluminum form in soil is generally Al 3+ and aluminum hydroxyl (Al(OH) 2+ 、Al(OH)2 + and Al(OH)3, etc., if all active aluminum is regarded as Al 3+ The calculated lime requirement for improving acidic soil is higher than the actual lime requirement. The present invention establishes a correction equation based on the relationship between the active aluminum form and the soil pH, and the lime requirement calculated based on this equation is more accurate.

[0036] (4) The determination of aluminum in the laboratory uses ultraviolet-visible spectrophotometry or atomic absorption spectrophotometry, which is difficult to perform under field conditions. The present invention forms a blue complex with active aluminum and chrome azuroin S in the pH range of 5.7 to 6.1, and then uses a lightweight colorimeter to measure the color difference value of the active aluminum color development solution to be tested. The aluminum concentration is calculated based on the quantitative relationship between the color difference value and the aluminum concentration. The colorimeter has the advantages of low price, small size, light weight, and the ability to be equipped with a removable battery. Combining it with the solution colorimetry method can realize the field determination of active aluminum in acidic soil. Therefore, the present invention provides a feasible method for the determination of active aluminum in soil under field conditions, solves the problem of time-consuming and labor-intensive determination of lime requirements when improving acidic soils, and greatly improves the efficiency of diagnosis and decision-making for improving acidic soils. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Graph showing the linear relationship between the aluminum concentration and the color difference ΔE of a series of aluminum standard solutions measured using chrome azurol S in combination with a colorimeter in Example 1;

[0038] Figure 2 This is a linear relationship diagram between the aluminum concentration and the color difference value ΔE of a series of aluminum standard solutions measured using catechol purple in combination with a colorimeter;

[0039] Figure 3 This is a linear relationship diagram between the aluminum concentration and the color difference value ΔE of a series of aluminum standard solutions measured using hematoxylin and a colorimeter;

[0040] Figure 4 This is a linear relationship diagram between the aluminum concentration and the color difference value ΔE of a series of aluminum standard solutions measured using an aluminum reagent and a colorimeter;

[0041] Figure 5 This is a linear relationship diagram between the aluminum concentration and the color difference value ΔE of a series of aluminum standard solutions measured by using tirazole and a colorimeter;

[0042] Figure 6 This is the linear correlation diagram of the results of soil active aluminum content extraction by elution method and single equilibrium method;

[0043] Figure 7 This is a comparison chart of the active aluminum content measured in the field and in the laboratory three months after treatment of acidic soils treated with Example 2 and Comparative Examples 1-2, wherein the control is Comparative Example 1, Treatment 2 is Example 2, and Treatment 3 is Comparative Example 2;

[0044] Figure 8 This is a comparison of soil active aluminum content measured three months after field conditions and air-dried soil in acidic soil treated with Example 2 and Comparative Examples 1-2, wherein the control is Comparative Example 1, Treatment 2 is Example 2, and Treatment 3 is Comparative Example 2;

[0045] Figure 9This is a comparison chart of rapeseed yield after planting rapeseed in acidic soil treated with Example 2 and Comparative Examples 1-2, wherein the control is Comparative Example 1, Treatment 2 is Example 2, and Treatment 3 is Comparative Example 2. DETAILED DESCRIPTION

[0046] The present invention provides a method for determining the amount of lime required for improving acidic soil under field conditions, comprising the following steps:

[0047] (1) Adding the soil sample to a potassium chloride solution, shaking it manually, letting it stand, and filtering it to obtain an active aluminum extract;

[0048] (2) mixing the active aluminum extract, the mixed color developer, the masking agent, and the pH buffer solution to obtain an active aluminum color developer solution, then preparing an aluminum standard solution color developer solution, measuring the color difference ΔE of the aluminum standard solution, and establishing a standard curve of aluminum concentration and color difference ΔE;

[0049] (3) Determine the color difference of the active aluminum test solution and calculate the aluminum concentration [Al] (mmol / L) in the active aluminum extract and the active aluminum content [Al] in the soil according to the standard curve. act (mmol / kg);

[0050] (4) If the active aluminum content [Al] act >2.00mmol / kg, it is determined that the soil needs to be improved, otherwise no improvement is needed;

[0051] (5) Mix lime and water, and titrate the resulting mixed suspension with hydrochloric acid solution to a pH of 5.5-6.0. Record the consumption of hydrochloric acid solution V, and calculate the acid neutralization capacity ANC of the lime according to formula (1):

[0052]

[0053] Wherein, V is the consumption of hydrochloric acid solution, in mL;

[0054] C is the concentration of hydrochloric acid solution, in mol / L;

[0055] m is the mass of lime, in g;

[0056] ANC is the acid neutralization capacity of lime, in mol / kg;

[0057] (6) After mixing the soil sample with water, measure the pH value of the soil and calculate the molar ratio of active aluminum in the soil [OH] / [Al] according to formula (2):

[0058]

[0059] (7) Calculate the lime requirement LR for improving acidic soil according to formula (3):

[0060]

[0061] Where ρ is the soil bulk density in g / cm 3 ;

[0062] [Al] act is the active aluminum content in the soil, in mmol / kg;

[0063] [Al] is the concentration of aluminum, in [mmol / L];

[0064] LR is the lime requirement in kg / ha.

[0065] In the present invention, the amount of lime required for improving acidic soil is calculated based on a soil layer thickness of 0 to 20 cm.

[0066] In the present invention, in step (1), the mass volume ratio of the soil sample to the potassium chloride solution is 1-3 g:20-30 mL, preferably 1.5-2.5 g:22-28 mL, and more preferably 2 g:25 mL, wherein the concentration of the potassium chloride solution is 0.5-1.5 mol / L, preferably 1.0 mol / L.

[0067] In the present invention, in step (1), the hand shaking time is 1 to 3 minutes, preferably 2 minutes, and the standing time is 20 to 40 minutes, preferably 25 to 35 minutes, and more preferably 30 minutes.

[0068] In the present invention, in step (2), the mixed developer is prepared by mixing a chrome azurol S solution and a cetyltrimethylammonium bromide solution to obtain a mixed developer.

[0069] In the present invention, the chrome azure S solution is prepared by mixing chrome azure S and water, wherein the mass volume ratio of chrome azure S to water is 1g:400~600mL, preferably 1g:420~580mL, and more preferably 1g:450~550mL; the cetyltrimethylammonium bromide solution is prepared by mixing cetyltrimethylammonium bromide and ethanol, wherein the mass volume ratio of cetyltrimethylammonium bromide to ethanol is 1g:40~60mL, preferably 1g:45~55mL, and more preferably 1g:50mL; the volume ratio of the chrome azure S solution to the cetyltrimethylammonium bromide solution is 40~60:4~6, and preferably 50:5.

[0070] In the present invention, the masking agent is an ascorbic acid solution, wherein the mass volume ratio of ascorbic acid to water is 1 g:90-110 mL, preferably 1 g:95-105 mL, and more preferably 1 g:100 mL.

[0071] In the present invention, the pH buffer solution is an acetic acid-sodium acetate buffer solution, which is prepared by mixing sodium acetate trihydrate, glacial acetic acid and water, then transferring the mixture to a 1000mL volumetric flask to constant volume, and finally adjusting the pH value. The mass volume ratio of sodium acetate trihydrate, glacial acetic acid and water is 120-150g:10-15mL:800-1000mL, and the pH value is adjusted to 5.7-6.1.

[0072] In the present invention, the volume ratio of the active aluminum extract, mixed color developer, masking agent and pH buffer solution is 0.1-1:2-5:0.8-1.2:2-5, preferably 0.2-0.8:2.5-4:0.9-1.1:2.5-4, and more preferably 0.2-0.6:2.5-3:1.0:2.5-3.

[0073] In the present invention, the calculation formula of the color difference value ΔE is the Euclidean formula:

[0074]

[0075] In the present invention, in step (5), the mass volume ratio of lime to water is 1g:300-500mL, preferably 1g:350-450mL, and more preferably 1g:400mL.

[0076] In the present invention, in step (5), the concentration of the hydrochloric acid solution is 0.8 to 1.2 mol / L, preferably 0.9 to 1.1 mol / L, and more preferably 1.0 mol / L.

[0077] In the present invention, in step (6), the mass ratio of the soil sample to water is 1:2-3, preferably 1:2.5.

[0078] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0079] Preparation method of the mixed developer used in the embodiment: prepare a chrome azuro blue S solution according to the mass volume ratio of chrome azuro blue S and deionized water of 1g:500mL; prepare a cetyl trimethylammonium bromide solution according to the mass volume ratio of cetyl trimethylammonium bromide and anhydrous ethanol of 1g:50mL, then slowly pour the chrome azuro blue S solution into the cetyl trimethylammonium bromide solution and stir evenly to obtain a mixed developer.

[0080] Preparation method of the masking agent: according to the mass volume ratio of ascorbic acid to deionized water being 1 g:100 mL, ascorbic acid and deionized water are mixed evenly to obtain an ascorbic acid solution with a concentration of 10 g / L.

[0081] Preparation method of pH buffer solution: place 136g of sodium acetate trihydrate in a 1000mL beaker, add 15mL of glacial acetic acid, add 800mL of deionized water, stir evenly, transfer to a 1000mL volumetric flask and make up to volume, and finally adjust the pH of the solution to 5.9 with acetic acid or sodium hydroxide to obtain acetic acid-sodium acetate buffer solution.

[0082] Example 1

[0083] Eight types of acidic soils (see Table 1 for details) were collected from different regions at a sampling depth of 0 to 20 cm and naturally air-dried to obtain soil samples.

[0084] Grind the soil sample and pass it through a 60-mesh sieve. Use a 1 / 10,000 balance to weigh 1.0000 g of soil and place it in a 50 mL plastic centrifuge tube. Then add 25 mL of 1.0 mol / L potassium chloride solution. Shake by hand for 2 minutes, let it stand for 30 minutes, and filter it with a 0.45 μm filter membrane. The filtrate obtained is the active aluminum extract.

[0085] Take 0.2 mL of active aluminum extract and place it in a 25 mL colorimetric tube, then add 1 mL of ascorbic acid solution, 2.5 mL of mixed color developer, and 2.5 mL of acetic acid-sodium acetate buffer solution with a pH value of 5.9, then dilute to the scale with deionized water, shake well, and obtain the active aluminum color solution to be tested.

[0086] 0 mL, 0.25 mL, 0.50 mL, 0.75 mL, 1 mL, 1.25 mL, and 1.5 mL of a 100 μmol / L aluminum standard solution were taken and placed in 25 mL colorimetric tubes. 1 mL of ascorbic acid solution, 2.5 mL of a mixed color developer, and 2.5 mL of acetic acid-sodium acetate buffer solution with a pH of 5.9 were then added to the tubes. The volume was adjusted to the mark with deionized water and the solution was shaken to obtain a series of aluminum standard solution colorimetric solutions with aluminum concentrations of 0 μmol / L, 1 μmol / L, 2 μmol / L, 3 μmol / L, 4 μmol / L, 5 μmol / L, and 6 μmol / L, respectively. The aluminum standard solution colorimetric solutions were transferred to 1 cm glass cuvettes. The red (R), green (G), and blue (B) color values ​​of the aluminum standard solution colorimetric solutions were measured using a colorimeter from one side of the cuvette that was transparent. The other side of the cuvette was covered with white paper. The standard curve was established using the Euclidean formula, where ΔR, ΔG, and ΔB are the differences in R, G, and B after color development with different concentrations of aluminum standard solutions and the R, G, and B of the blank control (0 μmol / L aluminum standard solution color development solution). A standard curve was established with aluminum concentration as the x-axis and color difference value ΔE as the y-axis to obtain the linear relationship equation between aluminum concentration and color difference value, see Figure 1 .

[0087] Transfer the active aluminum colorimetric solution to be tested into a 1 cm glass cuvette, and use a colorimeter to measure the red (R), green (G), and blue (B) color values ​​of the aluminum standard solution colorimetric solution from one side of the cuvette, and cover the other side with white paper. Obtain the difference between the R, G, and B values ​​of the colorimetric solution to be tested and those of the blank control (0 μmol / L aluminum standard solution colorimetric solution), and calculate the ΔE of the colorimetric solution to be tested. Figure 1 The aluminum concentration in the active aluminum extract was calculated using the provided standard curve and formula, and then the active aluminum content in the soil was calculated (results are shown in Table 1).

[0088] Mix lime and water in a ratio of 1 g:400 mL and titrate with 1 mol / L hydrochloric acid solution to a pH of 6.0. Record the consumption of hydrochloric acid solution V and calculate the acid neutralization capacity of lime according to formula (1): ANC = 3.232 × 1 / 0.1 = 32.32 mol / kg.

[0089] The soil sample was ground and passed through a 10-mesh sieve. The soil sample and water were mixed evenly at a mass ratio of 1:2.5. The pH value of the soil was measured, and then the [OH] / [Al] molar ratio of active aluminum was calculated according to formula (2).

[0090] Finally, the lime requirement LR for improving acidic soil was calculated according to formula (3) (results are shown in Table 1).

[0091] The soil sample was ground, passed through a 10-mesh sieve, and placed in a 250 mL plastic beaker. Lime was added to the beaker according to the lime requirement calculated in Table 1. After mixing evenly, deionized water was added according to 30% of the maximum field water holding capacity of each soil.

[0092] The soil to which lime was added was placed in a constant temperature incubator and cultured at 25±1°C. Water was added every 3 days to maintain a basically stable moisture content. After 35 days of culture, the soil sample was taken out, air-dried, ground and passed through a 10-mesh sieve for soil pH determination. Another soil that had passed through the 10-mesh sieve was further ground and passed through a 60-mesh sieve for determination of soil active aluminum content. The test method was the same as above. The test results are shown in Table 1.

[0093] Table 1 Lime requirement of acidic soil and soil pH and active aluminum content before and after cultivation measured in Example 1

[0094]

[0095] As can be seen from Table 1, when the lime requirement is calculated according to the method provided by the present invention, the active aluminum content of various acidic soils is significantly reduced and the pH is significantly increased after adding lime to the soil for 35 days of incubation. This indicates that the lime requirement calculated by the method provided by the present invention can basically eliminate the harmful effects of active aluminum in acidic soils under the incubation experimental conditions.

[0096] Example 2

[0097] The determination of soil active aluminum and the calculation of lime requirement under field conditions were carried out in Xingqiao Town, Ji'an City, Jiangxi Province. A total of four plots were arranged, numbered Ⅰ, Ⅱ, Ⅲ, and Ⅳ. Each plot was divided into three experimental areas, namely Ⅰ-1, Ⅰ-2, Ⅰ-3, Ⅱ-1, Ⅱ-2, Ⅱ-3, Ⅲ-1, Ⅲ-2, Ⅲ-3, Ⅳ-1, Ⅳ-2, and Ⅳ-3. The area of ​​each experimental area was 10×3m 2 .

[0098] The five-point sampling method was used to collect soil samples from I-3, II-3, III-3, and IV-3, respectively, with a sampling depth of 0 to 20 cm. The soil samples collected from each experimental area were mixed evenly, and then 2.00 g of soil samples from different experimental areas were weighed using a 1% balance and placed in a 50 mL plastic centrifuge tube. 25 mL of 1.0 mol / L potassium chloride solution was then added, and the tubes were shaken by hand for 2 minutes and allowed to stand for 30 minutes. The tubes were filtered with a 0.45 μm filter membrane to obtain the filtrate, which was the active aluminum extract.

[0099] Take 0.2 mL of active aluminum extract and place it in a 25 mL colorimetric tube, then add 1 mL of ascorbic acid solution, 2.5 mL of mixed color developer, and 2.5 mL of acetic acid-sodium acetate buffer solution with a pH value of 5.9, then dilute to the scale with deionized water, shake well, and obtain the active aluminum color solution to be tested.

[0100] The R, G, and B color values ​​of the active aluminum color developing solution to be tested were determined according to the method of Example 1, and the differences between the R, G, and B of the active aluminum color developing solution to be tested and the R, G, and B of the blank control (0 μmol / L aluminum standard solution color developing solution) were obtained. The ΔE of the color developing solution to be tested was calculated according to the method of Example 1. Figure 1 The aluminum concentration in the active aluminum extract was calculated using the provided standard curve and formula, and then the active aluminum content in the soil was calculated (results shown in Table 2). It can be seen from Table 2 that the active aluminum content was higher than 10.00 mmol / kg, so the soil needed to be improved.

[0101] Mix lime and water in a ratio of 1 g:400 mL and titrate with 1 mol / L hydrochloric acid solution to a pH of 6.0. Record the consumption of hydrochloric acid solution V and calculate the acid neutralization capacity of lime according to formula (1): ANC = 3.232 × 1 / 0.1 = 32.32 mol / kg.

[0102] The soil sample and water were mixed evenly at a mass ratio of 1:2.5, the pH value of the soil was measured, and then the molar ratio of [OH] / [Al] of active aluminum was calculated according to formula (2).

[0103] Finally, the lime requirement LR for improving acidic soil was calculated according to formula (3) (results are shown in Table 2).

[0104] Lime was applied according to the lime requirement in Table 2. After lime application, the surface soil was tilled evenly. Three months later, soil samples were collected again and the active aluminum content was determined again using the RGB method.

[0105] Comparative Example 1

[0106] For the experimental areas I-1, II-1, III-1, and IV-1 set up in Example 2, soil samples were collected according to the method of Example 2, and then the pH value and active aluminum content were measured. However, the soil in the experimental areas I-1, II-1, III-1, and IV-1 was not improved. The test results are shown in Table 2.

[0107] Comparative Example 2

[0108] For the experimental areas I-2, II-2, III-2, and IV-2 set in Example 2, soil samples were collected according to the method of Example 2, and then the pH value and active aluminum content were measured. The difference from Example 2 was that the lime requirement was calculated using the pH buffer capacity, where the pH buffer capacity was 31.44 mmol / kg / pH and the soil bulk density ρ was 1.3 g / cm 3 , the target soil pH is 5.5, and the calculated lime requirement results are shown in Table 2.

[0109] Table 2 Test results and lime requirements of Example 2 and Comparative Examples 1-2

[0110]

[0111] Three months later, the soil active aluminum was measured in the experimental areas of Example 2, Comparative Example 1 and Comparative Example 2. The results are as follows: Figure 7 As shown. Figure 7 It can be seen that under field conditions, after applying the lime dosage calculated based on the active aluminum content determined by the RGB method and the soil pH, the soil active aluminum content decreased from 12.71 mmol / kg in Comparative Example 1 to 1.63 mmol / kg, and the relative deviation between the field active aluminum content determination results and the laboratory determination results was between 0.6 and 2.1%. It can be considered that there is no difference in the determination results of the two methods. Compared with Comparative Example 1, the soil active aluminum content in Comparative Example 2 decreased from 12.71 mmol / kg to 4.68 mmol / kg, and the improvement effect was worse than that in Example 2. This shows that compared with the improvement effect of the lime dosage calculated based on the pH buffering capacity on soil acidity, the lime dosage calculated by the method of the present invention has a better improvement effect on soil acidity. The above results show that the acidic soil improvement scheme formulated by the present invention based on the on-site determination results of soil active aluminum under field conditions is reliable and feasible.

[0112] For the experimental areas in Example 2 and Comparative Examples 1-2, soil samples were collected from different experimental areas after rain. The soil moisture content was first determined using the alcohol combustion method under field conditions, and then the active aluminum content in the soil was determined. In addition, the collected soil samples were sealed and brought back to the laboratory, and the soil moisture content was determined using the drying method. The results were compared with the soil moisture content determined using the alcohol combustion method under field conditions. The results are shown in Table 3.

[0113] Table 3 Results of soil moisture determination by field alcohol combustion method and laboratory drying method

[0114]

[0115] As can be seen from Table 3, the relative deviation of the two methods for determining soil moisture content is within ±8.9%, indicating that the alcohol combustion method can replace the drying method for determining soil moisture content under field conditions.

[0116] The method for determining soil active aluminum under field conditions is described in Example 2. After the soil samples were air-dried in the laboratory, the soil active aluminum content was determined using a similar method under laboratory conditions and compared with the results obtained under field conditions. Figure 8 As shown. Figure 8 It can be seen that by comparing the active aluminum determination results after considering the soil moisture content under field conditions and the determination results of the air-dried soil in the laboratory, the relative deviation of the determination results of the two methods is within ±5.2%, indicating that the method of using the alcohol combustion method to determine the soil moisture content under field conditions is feasible.

[0117] The present invention planted rapeseed in three treatment plots, and measured the rapeseed yield in each treatment plot after harvest to verify the improvement effect of soil acidity. The results are shown in Figure 9. Figure 9 It can be seen that Example 2 and Comparative Example 2 significantly increased rapeseed yield compared to Comparative Example 1. This indicates that the lime requirement calculated based on soil active aluminum and pH and the lime requirement calculated based on pH buffering capacity can both significantly increase rapeseed yield, with significant differences compared to the control group (Comparative Example 1).

[0118] The present invention uses different types of color developers in conjunction with a colorimeter to measure aluminum concentration. The specific process is as follows:

[0119] (1) Determination of aluminum concentration using catechol violet in combination with a colorimeter: 0 mL, 1 mL, 2 mL, 3 mL, 4 mL, and 5 mL of a 60 μmol / L aluminum standard solution were taken, respectively, and placed in a 25 mL colorimetric tube. Then, 2 mL of a hydroxylamine hydrochloride-phenanthroline mixed solution, 2 mL of catechol violet color developer, and 5 mL of a hexamethylenetetramine buffer solution with a pH value of 6.2 were added to the above colorimetric tubes, respectively. The volume was adjusted to the scale line with deionized water, and the solution was shaken to obtain a series of aluminum standard solution colorimetric solutions with aluminum concentrations of 0 μmol / L, 2.4 μmol / L, 4.8 μmol / L, 7.2 μmol / L, 9.6 μmol / L, and 12 μmol / L, respectively.

[0120] The hydroxylamine hydrochloride-o-phenanthroline mixed solution was prepared by weighing 10 g of hydroxylamine hydrochloride and 0.15 g of o-phenanthroline and dissolving them in 80 mL of deionized water. The solution was then transferred to a 100 mL volumetric flask and diluted to 100 mL with deionized water.

[0121] The preparation method of the catechol violet color developer is as follows: 0.15 g of catechol violet is weighed and dissolved in 100 mL of deionized water.

[0122] The preparation method of the hexamethylenetetramine buffer is as follows: first, a 20% hexamethylenetetramine solution is prepared, and then the pH of the solution is adjusted to 6.2 with dilute hydrochloric acid.

[0123] Then, the colorimetric solution of the aluminum standard solution was measured according to the method of Example 1, and a standard curve was established to obtain a linear relationship equation between aluminum concentration and color difference value, as shown in FIG. Figure 2 .

[0124] from Figure 2 It can be seen that within the aluminum concentration range of 0 to 12 μmol / L, there is no good linear relationship between the RGB color difference value ΔE of the standard solution and the aluminum concentration, and the correlation coefficient is less than 0.97.

[0125] (2) Determination of aluminum concentration using hematoxylin in combination with a colorimeter: 0 mL, 0.1 mL, 0.2 mL, 0.3 mL, and 0.4 mL of a 10 mg / L aluminum standard solution were taken, respectively, and placed in a 25 mL colorimetric tube. Then, 2 mL of hematoxylin colorimetric reagent and 10 mL of cetyltrimethylammonium bromide solution were added to the above colorimetric tubes, respectively. The volume was then made up to 25 mL with hexamethylenetetramine buffer (pH 7.5). After shaking, the solution was color developed at room temperature for 1 h to obtain a series of aluminum standard solution colorimetric solutions with aluminum concentrations of 0 mg / L, 0.04 mg / L, 0.08 mg / L, 0.12 mg / L, and 0.16 mg / L, respectively.

[0126] The preparation method of the above-mentioned hematoxylin color developer is as follows: 0.1 g of hematoxylin is dissolved in 100 mL of ethanol.

[0127] The above-mentioned cetyltrimethylammonium bromide solution was prepared by dissolving 3.65 g of cetyltrimethylammonium bromide in 800 mL of deionized water, then transferring the solution to a 1 L volumetric flask and diluting the volume to 1 L with deionized water.

[0128] The preparation method of the hexamethylenetetramine buffer solution with a pH of 7.5 is as follows: first prepare a 10% hexamethylenetetramine solution, and then adjust the pH to 7.5 with dilute hydrochloric acid.

[0129] Then, the colorimetric solution of the aluminum standard solution was measured according to the method of Example 1, and a standard curve was established to obtain a linear relationship equation between aluminum concentration and color difference value, as shown in FIG. Figure 3 .

[0130] from Figure 3 It can be seen that within the aluminum concentration range of 0 to 0.16 mg / L, there is no good linear relationship between the RGB color difference value ΔE of the standard solution and the aluminum concentration, and the correlation coefficient is less than 0.96.

[0131] (3) Determination of aluminum concentration using aluminum reagent and colorimeter:

[0132] To 25 mL colorimetric tubes, add 5 mL of pH 4.2 acetic acid-sodium acetate buffer, 1 mL of ascorbic acid, and 5 mL of aluminum reagent. Add 0 mL, 0.5 mL, 1 mL, 1.5 mL, 2 mL, and 2.5 mL of a 10 mg / L aluminum standard solution to the tubes, respectively, and finally dilute to 25 mL with deionized water. After shaking and allowing the solution to develop for 25 minutes, a series of aluminum standard solutions with aluminum concentrations of 0 mg / L, 0.2 mg / L, 0.4 mg / L, 0.6 mg / L, 0.8 mg / L, and 1.0 mg / L were obtained.

[0133] The pH 4.2 acetic acid-sodium acetate buffer solution was prepared as follows: 60 mL of glacial acetic acid was diluted to 900 mL with deionized water, 100 mL of 100 g / L sodium hydroxide solution was added, and then the pH was adjusted to 4.2 with acetic acid or 100 g / L sodium hydroxide solution.

[0134] The preparation method of the above-mentioned ascorbic acid is as follows: weigh 1g of ascorbic acid and dissolve it in 100mL of deionized water, and prepare it before use.

[0135] The aluminum reagent was prepared as follows: 0.2000 g of the aluminum reagent was weighed and dissolved in 100 mL of the acetic acid-sodium acetate buffer solution having a pH of 4.2, and then the volume was adjusted to 500 mL with deionized water for immediate use.

[0136] Then, the colorimetric solution of the aluminum standard solution was measured according to the method of Example 1, and a standard curve was established to obtain a linear relationship equation between aluminum concentration and color difference value, as shown in FIG. Figure 4 .

[0137] from Figure 4 It can be seen that within the aluminum concentration range of 0 to 1.0 mg / L, there is no good linear relationship between the RGB color difference value ΔE of the standard solution and the aluminum concentration, and the correlation coefficient is less than 0.98.

[0138] (4) Determination of aluminum concentration using a colorimeter combined with a colorimeter

[0139] Pipette 0 mL, 1 mL, 2 mL, 3 mL, and 4 mL of 10 mg / L aluminum standard solution into 25 mL colorimetric tubes respectively.

[0140] To each of the colorimetric tubes, 1 mL of 1 mol / L nitric acid solution was added, followed by 6 mL of acetic acid-sodium acetate buffer solution at pH 5.5 and 2 mL of tryptophan solution. Finally, 3 mL of 1 mol / L sodium hydroxide solution was added. Each solution was shaken evenly. After standing at room temperature for 24 hours, a colorimetric solution of a series of aluminum standard solutions with aluminum concentrations of 0 mg / L, 0.4 mg / L, 0.8 mg / L, 1.2 mg / L, and 1.6 mg / L was obtained.

[0141] The preparation method of the above nitric acid solution is: take 63mL of concentrated nitric acid and dilute it to 1L.

[0142] The acetic acid-sodium acetate buffer solution is prepared as follows: 10 g of sodium acetate trihydrate is weighed and dissolved in 100 mL of deionized water, and the pH is adjusted to 5.5 using glacial acetic acid or sodium hydroxide as indicated by a pH meter.

[0143] The preparation method of the above-mentioned ferrochlore solution is as follows: weigh 0.2g of ferrochlore reagent and dissolve it in 100mL of deionized water.

[0144] The sodium hydroxide solution was prepared by weighing 4.0 g of sodium hydroxide and dissolving it in deionized water, and then diluting the solution to 100 mL.

[0145] Then, the colorimetric solution of the aluminum standard solution was measured according to the method of Example 1, and a standard curve was established to obtain a linear relationship equation between aluminum concentration and color difference value, as shown in FIG. Figure 5 .

[0146] from Figure 5 It can be seen that within the aluminum concentration range of 0 to 1.0 mg / L, the RGB color difference value ΔE of the standard solution has a good linear relationship with the aluminum concentration, and the correlation coefficient reaches 0.9928.

[0147] from Figures 1 to 5It can be seen that in the aluminum concentration determination method using hematoxylin, catechol violet, aluminum reagent, and a colorimeter, there is no good linear relationship between the RGB color difference value ΔE of the standard solution and the aluminum concentration, with correlation coefficients of less than 0.98. In addition, the hematoxylin and catechol violet color development process uses hexamethylenetetramine, a dangerous chemical that is easily explosive and therefore difficult to transport and use in the field. In the aluminum concentration determination method using tinol and a colorimeter, there is a good linear relationship between the RGB color difference value ΔE of the standard solution and the aluminum concentration. However, this method has a display time of 24 hours, which is much longer than the color development time of the chrome azuro blue S method using a colorimeter. Therefore, the chrome azuro blue S method using a colorimeter is the optimal method for determining aluminum concentration in soil solution under field conditions.

[0148] The present invention compares the results of extracting soil active aluminum by the elution method and the single equilibrium method. The specific process is as follows:

[0149] (1) Leaching method: 35 kinds of acidic soils with a thickness of 0 to 20 cm were collected from different regions, naturally air-dried, ground and passed through a 60-mesh sieve. 4.0000 g of soil was accurately weighed on a sample paper using a 1 / 10,000 balance, and then transferred into a funnel covered with filter paper. The funnel was connected to a 100 mL volumetric flask. The soil sample was eluted with a 1 mol / L potassium chloride solution in small amounts and multiple times. When the filtrate was close to the scale of the volumetric flask, the volume was fixed with a 1 mol / L potassium chloride solution to obtain the extract of soil active aluminum extracted by the multiple elution method.

[0150] (2) Single-stage equilibrium method: Use a 1 / 10,000 balance to weigh 1.0000 g of soil into a 50 mL plastic centrifuge tube, then accurately add 25 mL of 1 mol / L potassium chloride solution, shake at 25°C for 30 min, and then centrifuge at 5000 rpm for 5 min. Filter the supernatant with filter paper to obtain the single-stage equilibrium soil active aluminum extract.

[0151] Then, the 8-hydroxyquinoline colorimetric method (pH 8.3) was used to determine the active aluminum content extracted by the two methods. The active aluminum content extracted by the single equilibrium method was used as the x-axis, and the active aluminum content extracted by the multiple elution method was used as the y-axis. A standard curve was established to obtain the linear relationship equation between the active aluminum content extracted by the two methods, as shown in Figure 2. Figure 6 shown.

[0152] Depend on Figure 6 The results show a good linear relationship between the active aluminum content extracted from soil using the single-equilibrium method and the multiple-elution method, and the difference in active aluminum content obtained from the same sample using the two methods is not significant. The slope of the standard curve is 1.0333, and the intercept is -0.3067, indicating that the active aluminum content extracted by the two methods is essentially the same.

[0153] The steps for determining aluminum content by 8-hydroxyquinoline colorimetric method (pH 8.3) are as follows: add aluminum standard solution (the concentration of aluminum standard stock solution is 0.01 mol / L, and the concentration of standard series is: 0.25, 0.5, 1.0, 2.0, 3.0 (×10 -5 mol / L)) and the test solution (the concentration after volume adjustment does not exceed 3.0×10 -5 mol / L), add an appropriate amount of distilled water to a final volume of 15 mL, add 1 mL of 2.5% 8-hydroxyquinoline solution, add 3 drops of phenol red solution as an indicator, and use a dropper to add 0.5 mol / L ammonia solution, shaking the centrifuge tube while adding until the solution just turns red. At this point, the solution pH is around 8.3. Add 1 mL of 20% ammonium acetate buffer solution at pH 8.3 to maintain a constant pH during the reaction. Add 5 mL of butyl acetate, cap the tube tightly, and shake vigorously by hand for 15 seconds. Let stand for at least 30 seconds to allow the ester and aqueous phases to separate. Use a pipette to aspirate the upper ester phase solution, and measure the absorbance at 395 nm using a UV-Vis spectrophotometer and a quartz cuvette.

[0154] To prepare the aluminum standard stock solution, accurately weigh 0.2698 g of pure aluminum foil (at least 99.5%) and completely dissolve it in 20 mL of concentrated HCl. Transfer the solution to a 1-liter volumetric flask and bring the volume up to the mark. This solution has a concentration of 0.01 mol / L. This solution serves as the stock solution for preparing aluminum standard solutions of other concentrations as needed.

[0155] The 2.5% 8-hydroxyquinoline solution was prepared as follows: 2.5 g of 8-hydroxyquinoline was dissolved in 6.5 mL of glacial acetic acid, and the volume was made up to 100 mL with deionized water. The solution was stored in a plastic bottle in a dark place and kept at low temperature.

[0156] The phenol red indicator was prepared as follows: 0.1 g of phenol red was weighed and dissolved in 28 mL of 0.01 mol / L NaOH solution, diluted to 250 mL, and stored in a plastic bottle.

[0157] The preparation method of the above 0.5 mol / L ammonia water is as follows: measure 17 mL of concentrated ammonia water, dilute it to 500 mL, and store it in a plastic bottle.

[0158] The preparation method of the above-mentioned 20% ammonium acetate buffer solution with a pH of 8.3 is as follows: 100 g of ammonium acetate is weighed, dissolved in deionized water and the volume is adjusted to 500 mL, and then concentrated ammonia water is used to adjust the pH to 8.3 as indicated by a pH meter.

[0159] The present invention compares the measurement results of the RGB method and the commonly used 8-hydroxyquinoline colorimetric method, and the specific process is as follows:

[0160] Seventeen different acidic soils (0-20 cm thick) were collected from different regions, air-dried, and ground through a 60-mesh sieve. Using a 1 / 10,000 balance, 4.0000 g of soil was accurately weighed onto a paper sample. The soil was then transferred to a filter paper-lined funnel connected to a 100 mL volumetric flask. The soil sample was then eluted with 1 mol / L potassium chloride solution in small, repeated doses. When the filtrate reached the mark, the volume was adjusted with 1 mol / L potassium chloride solution to obtain the soil active aluminum extract. 0.2 mL of the active aluminum extract was pipetted into a 25 mL colorimetric tube. 1 mL of ascorbic acid solution, 2.5 mL of a mixed developer (chrome azurol S and cetyltrimethylammonium bromide), and 2.5 mL of a pH 5.9 acetic acid-sodium acetate buffer solution were added to the tubes. The volume was then adjusted to the mark with purified water and shaken to mix.

[0161] Transfer the color-developing solution into 1 cm glass cuvettes. Measure the red (R), green (G), and blue (B) color values ​​of the color-developing solution using a colorimeter from one side of the cuvette that is transparent to light, while covering the other side with white paper.

[0162] The R, G, and B values ​​of the colorimetric solution to be tested were obtained, and the differences between the R, G, and B values ​​of the colorimetric solution of the blank solution (0 μmol / L aluminum standard solution) in Example 1 were calculated to obtain the ΔE value of the colorimetric solution to be tested. The concentration of aluminum in the active aluminum extract was calculated according to the standard curve and formula provided in Example 1, and the active aluminum content in the soil was further calculated. The results are shown in Table 1.

[0163] The aluminum concentration in the active aluminum extract was determined using the commonly used 8-hydroxyquinoline colorimetric method (pH 8.3) for comparison with the results of the RGB method of the present invention. The results are detailed in Table 4.

[0164] Table 4 Comparison of soil active aluminum content determined by RGB method and 8-hydroxyquinoline colorimetry

[0165]

[0166] As shown in Table 4, the aluminum content determined by the RGB method of the present invention is consistent with the value determined by the commonly used 8-hydroxyquinoline colorimetric method (pH 8.3), and the relative deviation is within ±5%, which shows that the RGB method of the present invention can accurately determine the actual active aluminum content in acidic soil.

[0167] The active aluminum extract from the acidic soil in Langxi, Anhui Province was used as a sample for a spiked experiment. The aluminum concentration after spiked was then detected using the RGB method of the present invention and the recovery rate was calculated. The specific spiked concentrations and recoveries are shown in Table 5.

[0168] Table 5 Recovery test results of activated aluminum extract from Langxi acidic soil in Anhui Province after spiked

[0169] Spike concentration (μmol / L) Measured concentration (μmol / L) Recovery rate 0 1.73 —— 1 2.66 95.8 2 3.73 100.1 3 4.80 104.1

[0170] Spiked recovery rates within the range of 95% to 105% meet the requirements for trace analysis. Spiked recovery rates were measured on acidic soils from Langxi, Anhui Province, with recoveries ranging from 95.8% to 104.1%. This demonstrates that the RGB method for determining active aluminum content is suitable for actual acidic soils and provides accurate results that meet the requirements for trace analysis.

[0171] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for determining lime requirements for improving acidic soil under field conditions, characterized in that: The steps include: (1) Adding the soil sample to a potassium chloride solution, shaking it manually, letting it stand, and filtering it to obtain an active aluminum extract; In the step (1), the hand shaking time is 1 to 3 minutes; the standing time is 20 to 40 minutes; (2) Mixing the active aluminum extract, the mixed color developer, the masking agent, and the pH buffer solution to obtain the active aluminum color developer to be tested, and then preparing the aluminum standard solution color developer. The aluminum standard solution color developer is transferred to a 1 cm glass cuvette, and the red (R), green (G), and blue (B) color values ​​of the aluminum standard solution color developer are measured from the light-transmitting side of the cuvette using a colorimeter. The difference between the R, G, and B values ​​of the aluminum standard solution after color development at different concentrations and the R, G, and B values ​​of the blank control are obtained, and the color difference value ΔE of the aluminum standard solution is calculated. A standard curve of aluminum concentration and color difference value ΔE is established; In the step (2), the mixed developer is prepared by mixing a chrome azurol S solution and a cetyltrimethylammonium bromide solution to obtain a mixed developer; (3) The active aluminum test solution was transferred to a 1 cm glass cuvette. The red (R), green (G), and blue (B) color values ​​of the aluminum test solution were measured using a colorimeter from the light-transmitting side of the cuvette. The R, G, and B values ​​of the test solution were compared with those of the blank control. The color difference value ΔE of the active aluminum test solution was calculated. The aluminum concentration [Al] in the active aluminum extract and the active aluminum content [Al] in the soil were calculated based on the standard curve. act ; (4) If the active aluminum content [Al] act >2.00mmol / kg, it is determined that the soil needs to be improved, otherwise no improvement is needed; (5) Mix lime and water, and titrate the resulting mixed suspension with hydrochloric acid solution to a pH of 5.5-6.

0. Record the consumption of hydrochloric acid solution V, and calculate the acid neutralization capacity ANC of the lime according to formula (1): Wherein, V is the consumption of hydrochloric acid solution, in mL; C is the concentration of hydrochloric acid solution, in mol / L; m is the mass of lime, in g; ANC is the acid neutralization capacity of lime, in mol / kg; (6) After mixing the soil sample with water, measure the pH value of the soil and calculate the molar ratio of active aluminum in the soil [OH] / [Al] according to formula (2): (7) Calculate the lime requirement LR for improving acidic soil according to formula (3): Where ρ is the soil bulk density in g / cm 3 ; [Al] act is the active aluminum content in the soil, in mmol / kg; [Al] is the concentration of aluminum, in [mmol / L]; LR is the lime requirement in kg / ha.

2. The method for determining lime requirement for improving acidic soil under field conditions according to claim 1, characterized in that: In the step (1), the mass volume ratio of the soil sample to the potassium chloride solution is 1-3 g: 20-30 mL, wherein the concentration of the potassium chloride solution is 0.5-1.5 mol / L.

3. The method for determining lime requirement for improving acidic soil under field conditions according to claim 1, characterized in that: The chrome azure blue S solution is prepared by mixing chrome azure blue S and water, wherein the mass volume ratio of chrome azure blue S to water is 1 g:400-600 mL; the cetyl trimethylammonium bromide solution is prepared by mixing cetyl trimethylammonium bromide and ethanol, wherein the mass volume ratio of cetyl trimethylammonium bromide to ethanol is 1 g:40-60 mL; and the volume ratio of the chrome azure blue S solution to the cetyl trimethylammonium bromide solution is 40-60:4-6.

4. The method for determining lime requirement for improving acidic soil under field conditions according to claim 2 or 3, characterized in that: In the step (5), the mass volume ratio of lime to water is 1g:300-500mL.

5. The method for determining lime requirement for improving acidic soil under field conditions according to claim 4, characterized in that: In the step (5), the concentration of the hydrochloric acid solution is 0.8 to 1.2 mol / L.

6. The method for determining lime requirement for improving acidic soil under field conditions according to claim 3 or 5, characterized in that: In the step (6), the mass ratio of the soil sample to water is 1:2-3.

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