Calcareous soil exchangeable salt base and salt base total amount determination method

Abstract

The invention provides a calcareous soil exchangeable salt base and salt base total amount determination method, which comprises the following steps: putting soil to be measured and a magnetic stirrer into a centrifuge tube, adding an ammonium chloride-ethanol exchange liquid, putting the centrifuge tube on a magnetic stirrer, carrying out magnetic stirring for 3-5 minutes while keeping vortex on the liquid surface in the stirring process, and filtering to obtain filtrate; and filtering and collecting filtrate, and determining and analyzing the exchangeable salt base and the total amount of the salt base in the calcareous soil. According to the method, the overnight standing time is saved, and more than 110mL of 70% ethanol solution for salt leaching can be saved when one sample is measured; the exchange reaction only needs one time, and the reaction time is only 3 minutes; the pH value of the ammonium chloride-ethanol exchange liquid does not need to be adjusted; according to the method, 50mL of ammonium chloride-ethanol exchange liquid is needed for each sample, and compared with a corresponding method for measuring each sample, the usage amount of ammonium chloride is saved by 80%, and the usage amount of 70% ethanol is saved by 80%. The working efficiency is greatly improved; and the reagent usage amount is reduced.

Description

Technical Field

[0001] The invention belongs to the field of soil exchangeable base determination, and in particular relates to a method for determining the exchangeable base and the total amount of base in calcareous soil. Background Art

[0002] Soil cation exchange capacity (CEC) refers to the capacity of soil to adsorb and exchange cations, expressed as centimoles of monovalent ions per kilogram of soil, i.e. cmol / kg. Cation exchange capacity is related to the specific surface area and surface charge of soil colloids. Usually, soil cation exchange capacity is obtained by replacing all cations adsorbed by the soil with known cations and then measuring the adsorption capacity of the known cations. Soil cation exchange capacity is a very important chemical property of soil. It directly reflects the soil's fertilizer retention, fertilizer supply and buffering capacity, and also plays an extremely important role in the migration and transformation of soil pollutants.

[0003] Soil exchangeable base mainly refers to the Ca2+ adsorbed on soil colloids. 2+ Mg 2+ , K + 、Na + Soil exchangeable base is one of the important criteria for judging soil quality. Its content, saturation and different ion ratios reflect different soil physical and chemical properties. It also plays an important role in maintaining soil nutrients and preventing soil degradation. 2+ Mg 2+ , K + It is a nutrient element necessary for plant growth. Its quantity and composition ratio affect the absorption and utilization of nutrients and water by plants, which in turn affects crop production and the ability of plants to resist drought, frost, diseases and pests. + It is an important basis for evaluating the soil alkalinization level and improving the alkalinized soil.

[0004] With the advancement of agricultural science and technology, the national soil survey, soil quality evaluation, soil fertility improvement, soil improvement, soil pollution control and high-standard farmland construction projects have been carried out, and the determination of soil exchangeable base composition has become increasingly frequent. In the determination of exchangeable base and total base of calcareous soil (Agricultural Industry Standard of the People's Republic of China, NY / T 1615-2008. 2008, Ministry of Agriculture and Rural Affairs of the People's Republic of China, Beijing, China Agricultural Press.), the sample is first added with 50mL 70% ethanol solution and shaken for 30 minutes, and then left to stand overnight. The next day, the soil was transferred to a funnel with filter paper and rinsed with 30mL 70% ethanol solution. After the eluent was filtered dry, 30mL ethanol solution was added to continue eluting, and repeated several times until there was no Cl − and SO 4 2−The reaction was stopped. Then take out the filter paper and soil, put them in a 250mL conical flask, add 100mL pH 8.5 0.1mol / L ammonium chloride-70% ethanol exchange solution, shake for 30 minutes, and filter into a 250mL volumetric flask. Continue eluting with the exchange solution until the constant volume mark. Before the exchange base extraction of the above-mentioned calcareous soil, it is necessary to add 70% ethanol solution and shake it, then let it stand overnight, which greatly increases the extraction time; when the filter paper and soil are placed in a conical flask for shaking, due to the large volume of the filter paper, it is extremely difficult to shake evenly, which seriously affects the completeness of the exchange reaction and greatly reduces the work efficiency, and is in urgent need of improvement.

[0005] The basic principle of NY / T 1615-2008 standard is: potassium, sodium, calcium and magnesium in calcareous soil exist in the form of water-soluble salts, some of which are adsorbed by soil colloids, and there are also a large number of free calcium carbonate, magnesium carbonate and other insoluble salts. 2 H 5 OH) = 70%] to wash away the soluble chloride and sulfate in the soil, and then use ammonium chloride [c(NH 4 Cl)=0.1mol / L]-ethanol solution [φ(C 2 H 5 OH)=70%] to exchange potassium, sodium, calcium and magnesium adsorbed by soil colloids. Lower concentrations of ammonium chloride exchangers can reduce their salt effects, and higher pH values ​​and higher ethanol concentrations can inhibit the dissolution of insoluble carbonates and gypsum.

[0006] The contents of calcium and magnesium in the exchange solution are measured on an atomic absorption spectrophotometer, and the contents of potassium and sodium in the exchange solution are measured on a flame photometer. The sum of exchangeable potassium, sodium, calcium, and magnesium is the total amount of exchangeable bases. Summary of the invention

[0007] In view of the problem of low working efficiency caused by overnight standing, repeated salt washing, multiple exchange treatments, and the need to adjust the pH value of the exchange solution in the NY / T 1615-2008 standard, the present invention provides a method for determining the exchangeable base and the total amount of base in calcareous soil. By changing the exchange method and simultaneously determining the cation exchange capacity, the effect of omitting the overnight standing, omitting the salt washing step, reducing the number of exchanges, reducing the amount of exchange agent used, and omitting the adjustment of the pH value of the exchange solution is achieved, thereby improving the determination efficiency of the exchangeable base and the total amount of base in the soil.

[0008] In order to achieve the purpose of the present invention, the technical solution provided by the present invention is:

[0009] The invention provides a method for determining exchangeable base and total base amount of calcareous soil, which is characterized by: placing soil to be tested and a magnetic stirrer into a centrifuge tube, adding ammonium chloride-ethanol exchange solution, placing the centrifuge tube on a magnetic stirrer for magnetic stirring, maintaining a vortex on the liquid surface during the stirring process, the stirring time is 3-5 minutes, filtering and collecting the filtrate, and performing determination and analysis of the exchangeable base and total base amount; the soil to be tested is calcareous soil; wherein the soil cation exchange capacity is calculated according to the difference in ammonium ion concentration in the exchange solution before and after the exchange; and the exchangeable sodium is calculated by a difference method, that is, the exchangeable sodium=cation exchange capacity-(exchangeable calcium+exchangeable magnesium+exchangeable potassium).

[0010] Preferably, the calculation formula of the soil cation exchange capacity CEC is:

[0011]

[0012] Where:

[0013] CEC—cation exchange capacity of soil sample, cmol / kg;

[0014] c 0 —NH in the exchange solution 4 + Initial concentration, mg / L;

[0015] c—NH in the test solution 4 + Concentration, mg / L;

[0016] V—the volume of exchange solution added to each sample, mL;

[0017] m—weight of air-dried sample, g;

[0018] 180—per cmol NH 4 + Mass, mg / cmol.

[0019] Preferably, the calculation formula for the exchangeable base and the total amount of base is:

[0020]

[0021]

[0022]

[0023]

[0024]

[0025] Where:

[0026] ρ(Ca), ρ(Mg), ρ(K)—respectively refer to the concentration values ​​of calcium, magnesium, and potassium in the test solution obtained by checking the standard working curve or solving the regression equation, in milligrams per liter (mg / L);

[0027] V—the volume of the liquid to be tested, in milliliters (mL);

[0028] m—the mass of the sample weighed, in grams (g);

[0029] 20.04, 12.16, 39.10—respectively calcium (1 / 2Ca 2+ )、Magnesium(1 / 2Mg 2+ ), potassium (K + ) is the numerical value of the molar mass of a substance in grams per mole (g / mol);

[0030] ts—dilution multiple;

[0031] 10—Conversion factor from millimole per kilogram to centimole per kilogram.

[0032] Preferably, 50 mL of ammonium chloride-ethanol exchange solution is used for every 5.00 g of soil to be tested.

[0033] Preferably, the depth of the vortex is 2-5 mm; and / or

[0034] The magnetic stirrer is of type A.

[0035] Preferably, the stirring time is 3 minutes.

[0036] Preferably, the preparation method of each liter of the ammonium chloride-ethanol exchange solution is: dissolve 5.35g of ammonium chloride in 70% ethanol solution and make up to 1000mL.

[0037] Preferably, before the soil to be tested is exchanged with the ammonium chloride-ethanol exchange solution, it is not necessary to use a 70% ethanol solution to stand overnight and rinse to remove salt.

[0038] Preferably, when the soil to be tested is subjected to exchange reaction with the ammonium chloride-ethanol exchange solution, only one exchange treatment is required.

[0039] Preferably, the filtrate collected after the filtration does not need to be constant volume.

[0040] The beneficial effects of the present invention are:

[0041] When determining the exchangeable base and total base amount of calcareous soil, the NY / T 1615-2008 standard requires the addition of 50 mL of 70% ethanol solution for overnight standing and the 70% ethanol solution for leaching and washing salt. The present invention omits these steps, can save the time of standing overnight, and can save more than 110 mL of 70% ethanol solution for washing salt for each sample measured; the existing method requires 6 exchanges to complete the entire exchange reaction, while the present invention only requires 1 exchange reaction, and the reaction time is only 3 minutes, saving operation steps and time; the existing method requires the pH value of ammonium chloride-ethanol exchange solution to be adjusted to 8.5, while the present invention does not need to adjust, saving operation steps; the existing method requires 250 mL of ammonium chloride-ethanol exchange solution for each sample, while the present invention requires 50 mL, saving 80% of ammonium chloride usage and 80% of 70% ethanol usage for each sample measured compared with the corresponding method. The work efficiency is greatly improved and the reagent usage is saved. DETAILED DESCRIPTION

[0042] The following examples are provided for a better understanding of the present invention, but are not intended to limit the present invention. The experimental methods in the following examples are conventional methods unless otherwise specified. The experimental materials used in the following examples are purchased from conventional biochemical reagent companies unless otherwise specified. The quantitative tests in the following examples are repeated three times, and the results are averaged.

[0043] Compared with the NY / T 1615-2008 standard, the present invention is different in that: when preparing the ammonium chloride-ethanol exchange solution, the step of adjusting the pH value is omitted; the amount of each sample exchange solution added is 50 mL; the steps of standing overnight with 70% ethanol and rinsing the salt are omitted; a magnetic stirring bar is used for stirring, and specific conditions related to the magnetic stirring are defined; the number of exchanges to complete the entire exchange reaction is 1, and the reaction time only takes 3 minutes; and the exchangeable sodium content is calculated by using the difference subtraction method. The remaining steps are the same as the detection method in the NY / T1615-2008 standard.

[0044] Specifically, the present invention provides a method for determining the exchangeable base and the total amount of base in calcareous soil, comprising the following steps:

[0045] Weigh 5g (accurate to 0.01g) of the air-dried sample that has passed through a 2mm aperture sieve and place it in a 100mL centrifuge tube. Place a magnetic stirrer and add 50mL of ammonium chloride-ethanol exchange solution to the centrifuge tube. Place the centrifuge tube vertically on a magnetic stirrer for stirring. Adjust the stirring speed so that a 2-5mm deep vortex is maintained on the liquid surface during the stirring process. The stirring time is 3-5min. Then filter and collect the filtrate as the test solution. Do not use the exchange solution to make the volume constant. The filtrate is subjected to ammonium ion and exchangeable Ca 2+ Mg 2 + , K+ Determination and analysis. The soil cation exchange capacity (CEC) is calculated based on the difference in ammonium ion concentration in the exchange solution before and after the exchange. The determination and analysis method is as follows:

[0046] (1) The calculation formula of soil cation exchange capacity (CEC) is:

[0047]

[0048] Where:

[0049] CEC—cation exchange capacity of soil sample, cmol / kg;

[0050] c 0 —NH in the exchange solution 4 + Initial concentration, mg / L;

[0051] c—NH in the test solution 4 + Concentration, mg / L;

[0052] V—the volume of exchange solution added to each sample, mL;

[0053] m—weight of air-dried sample, g;

[0054] 180—per cmol NH 4 + Mass, mg / cmol.

[0055] (2) The calculation formula for exchangeable base and total base is:

[0056]

[0057]

[0058]

[0059]

[0060]

[0061] Where:

[0062] ρ(Ca), ρ(Mg), ρ(K)—respectively refer to the concentration values ​​of calcium, magnesium, and potassium in the test solution obtained by checking the standard working curve or solving the regression equation, in milligrams per liter (mg / L);

[0063] V—the volume of the liquid to be tested, in milliliters (mL);

[0064] m—the mass of the sample weighed, in grams (g);

[0065] 20.04, 12.16, 39.10—respectively calcium (1 / 2Ca 2+ )、Magnesium(1 / 2Mg 2+ ), potassium (K + ) is the numerical value of the molar mass of a substance in grams per mole (g / mol);

[0066] ts—dilution multiple;

[0067] 10—Conversion factor from millimole per kilogram to centimole per kilogram.

[0068] Wherein, the sample is calcareous soil.

[0069] The depth of the vortex is maintained at 2-5 mm, which ensures that the soil / exchange liquid mixture is always in suspension.

[0070] Preferably, the centrifuge tube is a round-bottom centrifuge tube, because such a centrifuge tube can fully exert the stirring effect of the magnetic stirrer.

[0071] Preferably, the magnetic stirrer is of type A, and a stirrer of this shape can rotate freely at the bottom of a round-bottom centrifuge tube, and both ends will not generate friction with the bottom of the centrifuge tube.

[0072] Preferably, the ammonium chloride-ethanol exchange solution is prepared by weighing 5.35 g of ammonium chloride (NH 4 Cl) is dissolved in an ethanol solution and fixed to 1000 mL; the ethanol solution is 70% ethanol, and the preparation method is as follows: measure 737 mL of ethanol solution [φ(C 2 H 5 OH)=95%] and diluted to 1000mL with water.

[0073] That is, the difference from Comparative Example 1 is that when preparing the ammonium chloride-ethanol exchange solution, the present invention does not need to adjust the pH to 8.5 with a 1:1 ammonia solution or a 1:1 hydrochloric acid solution.

[0074] Preferably, before the sample is exchanged with the ammonium chloride-ethanol exchange solution, it is not necessary to stand overnight with a 70% ethanol solution and rinse with salt.

[0075] Preferably, when the sample is subjected to exchange reaction with the ammonium chloride-ethanol exchange solution, only one exchange treatment is required.

[0076] Comparative Example 1 Determination of exchangeable base and total base amount of calcareous soil in NY / T 1615-2008 standard

[0077] 1 Reagents

[0078] The reagents used in this standard, unless otherwise specified, are analytically pure reagents that meet national standards; the solutions described in this standard are aqueous solutions unless the solvent is specified; the water used in this standard should comply with the requirements for secondary water in GB / T 6682.

[0079] 1.1 Ethanol solution, φ(C 2 H 5 OH)=70%:Measure 737mL of ethanol solution [φ(C 2 H 5 OH)=95%] and diluted to 1000mL with water.

[0080] 1.2 Ammonium chloride-ethanol exchange solution, the composition of which is ammonium chloride [c(NH 4 Cl) = 0.1 mol / L]-ethanol solution (1.1), pH 8.5: weigh 5.35 g of ammonium chloride (NH 4 Cl) was dissolved in 950 mL of ethanol solution (1.1), and then an aqueous ammonia solution (equal volumes of concentrated ammonia and water, i.e. V 浓氨水 :V 水 =1:1 volume ratio. Ammonia water purchased directly from a chemical reagent company is the concentrated ammonia water that meets the requirements, and you can directly measure the volume. Water is the experimental water that meets the requirements) or hydrochloric acid solution (concentrated hydrochloric acid and water mixed in equal volumes, that is, V 浓盐酸 :V 水 =1:1 volume ratio. The hydrochloric acid purchased directly from the chemical reagent company is the concentrated hydrochloric acid that meets the requirements, and the volume can be directly measured. Water is the experimental water that meets the requirements) to adjust the pH to 8.5, and then dilute to 1000mL with ethanol solution (1.1).

[0081] 1.3 Calcium standard solution, ρ(Ca)=1000mg / L: weigh 2.4973g of calcium carbonate (CaCO 3 , high-grade purity) in a 50mL beaker, add 10mL of water, and add hydrochloric acid solution (prepared in the same way as step 1.2) dropwise while stirring until all the calcium carbonate is dissolved. Heat to drive out carbon dioxide, cool, transfer to a 100mL volumetric flask, and dilute to the mark with water.

[0082] 1.4 Magnesium standard stock solution, ρ(Mg)=1000mg / L: Weigh 1.000g of magnesium metal (spectrally pure), add hydrochloric acid (super pure) solution (concentrated hydrochloric acid and water mixed in a volume ratio of 1:3, i.e. V 浓盐酸 :V 水 =1:3 volume ratio. The hydrochloric acid purchased directly from the chemical reagent company is the concentrated hydrochloric acid that meets the requirements, and the volume can be directly measured. Water is the experimental water that meets the requirements) Dissolve, dilute to 1000mL with water, and shake well.

[0083] 1.5 Magnesium standard solution, ρ(Mg)=100 mg / L: Pipette 10 mL of magnesium standard stock solution (1.4) into a 100 mL volumetric flask, dilute to the mark with water, and shake well.

[0084] 1.6 Potassium standard stock solution, ρ(K)=1000mg / L: Weigh 1.9069g of standard potassium chloride (KCl, extra-pure) that has been dried at 150℃ for 2h, dissolve it in water, make up to 1000mL, and store in a plastic bottle.

[0085] 1.7 Potassium standard solution, ρ(K)=100 mg / L: Pipette 10 mL of potassium standard stock solution (1.6) into a 100 mL volumetric flask, dilute to the mark with water, shake well, and store in a plastic bottle.

[0086] 1.8 Sodium standard stock solution, ρ(Na)=100 mg / L: Weigh 2.5422 g of standard sodium chloride (NaCl, extra pure) that has been dried at 150℃ for 2 h, dissolve it in water, make up to 1000 mL, and store in a plastic bottle.

[0087] 1.9 Sodium standard solution, ρ(Na)=100 mg / L: Pipette 10 mL of sodium standard stock solution (1.8) into a 100 mL volumetric flask, dilute to the mark with water, shake well, and store in a plastic bottle.

[0088] 1.10 Silver nitrate solution, ρ(AgNO 3 )=50g / L: Weigh 5.00g silver nitrate (AgNO 3 ) was dissolved in 100 mL of water and stored in a brown bottle.

[0089] 1.11 Barium chloride solution, ρ(BaCl 2 )=100g / L: Weigh 10.00g of barium chloride (BaCl 2 ) was dissolved in 100 mL of water.

[0090] 2 Instruments

[0091] 2.1 Reciprocating oscillator: The oscillation frequency should be between 150r / min and 180r / min.

[0092] 2.2 Atomic absorption spectrophotometer.

[0093] 2.3 Flame photometer.

[0094] 3 Analysis steps

[0095] 3.1 Weigh 5 g (accurate to 0.01 g) of the air-dried sample that has passed through a 2 mm pore size sieve, place it in a 250 mL conical flask, add 50 mL of ethanol solution (1.1), oscillate at a frequency of 150 r / min~180 r / min for 30 min, and let it stand overnight.

[0096] Transfer the soil to a funnel with filter paper and rinse with 30 mL of ethanol solution (1.1). After the eluent is filtered dry, add 30 mL of ethanol solution (1.1) and continue rinsing. Repeat several times until there is no Cl − and SO 4 2− until the reaction.

[0097] Take out the filter paper and soil, immediately place them in a 250mL conical flask, add 100mL of ammonium chloride-ethanol exchange solution (1.2), oscillate at a frequency of 150r / min~180r / min for 30min, and filter into a 250mL volumetric flask. Continue to rinse with ammonium chloride-ethanol exchange solution (1.2) in the same way as above until the volume mark is reached, shake well for testing. Perform a blank test at the same time.

[0098] In summary, "Take out the filter paper and soil, immediately place them in a 250mL conical flask, add 100mL of ammonium chloride-ethanol exchange solution (1.2), and oscillate at an oscillation frequency of 150r / min~180r / min for 30min", this is the first exchange. "Continue eluting with ammonium chloride-ethanol exchange solution (1.2), the method is the same as above", this sentence means that 30mL of ammonium chloride-ethanol exchange solution (1.2) is used for elution each time, and a total of 5 elutions are required, about 30×5=150 (mL). The entire operation process is equivalent to a total of 6 exchange reactions. The 6 additions of exchange solution and the process of transferring soil and filter paper will cause a large cumulative error, which will eventually cause a great inaccuracy in the volume of the filtrate, so it needs to be fixed to 250mL.

[0099] 3.2 Determination

[0100] 3.2.1 Drawing of standard working curve: Prepare a series of standard solutions as shown in Table 1. Take a certain amount of calcium, magnesium, potassium, and sodium standard solutions (1.3, 1.5, 1.7, and 1.9), place them in a set of 100 mL volumetric flasks, dilute to the mark with ammonium chloride-ethanol exchange solution (1.2), and shake well.

[0101] Table 1 Calcium, magnesium, potassium and sodium standard solution series

[0102]

[0103] 3.2.2 Sample determination: Use ammonium chloride-ethanol exchange solution (1.2) to calibrate the instrument zero point, determine calcium and magnesium on an atomic absorption spectrophotometer, and determine potassium and sodium on a flame photometer. Use concentration as the horizontal axis and absorbance as the vertical axis to draw standard working curves or find regression equations for calcium, magnesium, potassium, and sodium.

[0104] 4 Result calculation

[0105] Soil exchangeable basic calcium (Ca 2+ ), magnesium (Mg 2+ ), potassium (K + ), sodium (Na + ) and the total amount of bases are expressed as mass mole fraction S, expressed in centimole per kilogram (cmol / kg), calculated according to the following formula:

[0106]

[0107]

[0108]

[0109]

[0110]

[0111] Where:

[0112] ρ(Ca), ρ(Mg), ρ(K), ρ(Na)—respectively refer to the concentration values ​​of calcium, magnesium, potassium, and sodium in the test solution obtained by checking the standard working curve or solving the regression equation, in milligrams per liter (mg / L);

[0113] V—the value of the fixed volume of the liquid to be tested, in milliliters (mL);

[0114] m—the mass of the sample weighed, in grams (g);

[0115] 20.04, 12.16, 39.10, 22.99—respectively calcium (1 / 2Ca 2+ )、Magnesium(1 / 2Mg 2+ ), potassium (K + ), sodium (Na + ) is the numerical value of the molar mass of a substance in grams per mole (g / mol);

[0116] ts—dilution multiple;

[0117] 10—Conversion factor from millimole per kilogram to centimole per kilogram.

[0118] Example 1 A method for determining the exchangeable base and total base amount of calcareous soil according to the present invention

[0119] The difference between this embodiment and comparative example 1 lies in the following (1)-(4):

[0120] (1) Preparation of 0.1 mol / L ammonium chloride-70% ethanol exchange solution: 5.35 g of ammonium chloride was weighed and dissolved in 950 mL of 70% ethanol solution (Comparative Example 1, step 1.2), and then diluted to 1000 mL with 70% ethanol solution (Comparative Example 1, step 1.1) (i.e., the difference from Comparative Example 1 is that it is not necessary to adjust the pH to 8.5 with an aqueous ammonia solution or a hydrochloric acid solution).

[0121] (2) The analysis steps in step 3.1 of this embodiment are different from those in comparative example 1.

[0122] The analysis steps in this embodiment are as follows: weigh 5g (accurate to 0.01g) of the air-dried sample that has passed through a 2mm aperture sieve and put it into a 100mL round-bottomed centrifuge tube, put in a type A magnet, add 50mL of ammonium chloride-ethanol exchange solution into the centrifuge tube, vertically place the centrifuge tube on a magnetic stirrer and stir, adjust the stirring speed so that a 2-5mm deep vortex is maintained on the liquid surface during the stirring process, and the stirring time is 3min. Then filter, collect the filtrate as the liquid to be tested, and do not need to exchange the liquid to constant volume (the present invention is a single exchange method, and the exchange reaction is completed after a single exchange, and the exchangeable base ions all enter the filtrate. In addition, the present invention needs to calculate CEC based on the concentration difference of ammonium ions in the exchange solution before and after the exchange, and cannot be constant volume).

[0123] (3) This embodiment adds a step of measuring the cation exchange capacity of the soil.

[0124] The specific steps are: aspirate a certain volume of exchange solution and test solution respectively, and determine the NH 4 + The soil cation exchange capacity (CEC) was calculated according to the following formula:

[0125]

[0126] Where:

[0127] CEC—cation exchange capacity of soil sample, cmol / kg;

[0128] c 0 —NH in the exchange solution 4 + Initial concentration, mg / L;

[0129] c—NH in the test solution 4 + Concentration, mg / L;

[0130] V—the volume of exchange solution added to each sample, mL;

[0131] m—weight of air-dried sample, g;

[0132] 180—per cmol NH4 + Mass, mg / cmol.

[0133] (4) This example uses the difference method to calculate the exchangeable sodium.

[0134] That is, exchangeable sodium = cation exchange capacity - (exchangeable calcium + exchangeable magnesium + exchangeable potassium).

[0135]

[0136] The remaining steps and parameters are the same as those in Comparative Example 1.

[0137] Experimental Example 1 Determination of exchangeable base of standard calcareous soil at different reaction times

[0138] Two standard calcareous soils were selected, TMQC0255 pH value was 8.14±0.10, calcium carbonate content was 147±10 g / kg; TMQC0256 pH value was 8.80±1.10, calcium carbonate content was 137±9 g / kg. The exchangeable base ion content at different reaction times was determined by the method of Example 1 of the present invention, the reaction time was set to 1, 3 and 5 min, 3 parallel experiments were set for each sample, and the average value was taken. The results are shown in Table 2.

[0139] It can be seen from Table 2 that for the two standard soils, the exchangeable Ca 2+ Mg 2+ , K + 、Na + The measured value of the content was lower than the standard value range; there was no significant change in the measured results between 3 min and 5 min, both of which were within the standard value range. Therefore, the reaction time of 3 min was sufficient to complete the base exchange reaction of calcareous soil.

[0140] Table 2

[0141]

[0142] Experimental Example 2 Determination of exchangeable bases in calcareous soils with different calcium carbonate contents

[0143] The standard calcareous soil numbered GBW(E)070374 was selected, with a pH value of 8.27±0.16 and a calcium carbonate content of 181±22 g / kg. Using this as the reference soil, a certain amount of analytically pure calcium carbonate was added to form calcareous soils with calcium carbonate contents of 200 g / kg, 400 g / kg, and 600 g / kg. The exchangeable base content was determined by the methods of Comparative Example 1 and Example 1, and 3 parallel experiments were set for each sample to take the average value. The exchangeable base content of the four soils measured under the NY / T 1615-2008 standard and the method of Example 1 of the present invention are shown in Table 3.

[0144] As can be seen from Table 3, the exchangeable Ca content of calcareous soils with four kinds of calcium carbonate contents under the NY / T 1615-2008 standard and the method of Example 1 of the present invention is 2+ Mg 2+ , K + 、Na + The measured values ​​of the content are all within the standard value range, and both operation steps can produce accurate results. Compared with the NY / T 1615-2008 standard, the present invention omits the steps of adding 70% ethanol solution to stand overnight and 70% ethanol solution to wash the salt, saving time and reagent consumption. For each sample measured, more than 110 mL of 70% ethanol solution can be saved for washing the salt; the existing method requires 6 exchanges to complete the entire exchange reaction, while the present invention only requires 1 exchange reaction, and the reaction time is only 3 minutes, saving operation steps and time; the existing method requires the exchange liquid to adjust the pH value to 8.5, while the present invention does not need to adjust, saving operation steps; the existing method requires 250 mL of exchange liquid for each sample, while the present invention requires 50 mL, saving 80% of the use of ammonium chloride and 80% of the use of 70% ethanol for each sample measured compared with the corresponding method. Greatly improve work efficiency and save reagent usage.

[0145] Table 3

[0146]

[0147] Experimental Example 3 Determination of exchangeable base of actual calcareous soil

[0148] Five actual calcareous soils were selected to carry out the determination experiment of exchangeable base content using the methods in Comparative Example 1 and Example 1, and three parallel experiments were set for each sample to take the average value. The determination values ​​of the five soils under the conditions of NY / T 1615-2008 standard and the present invention are shown in Table 4.

[0149] It can be seen from Table 4 that the exchangeable Ca2+ content of five kinds of soils under the NY / T 1615-2008 standard and the method of Example 1 of the present invention is 2+ Mg 2+ , K + 、Na + The measured values ​​of the contents are all within the standard value range, and both operation steps can produce accurate results.

[0150] Table 4

[0151]

[0152] Experimental Example 4 Determination of exchangeable base of standard calcareous soil at different exchange solution pH values

[0153] Two standard calcareous soils were selected: TMQC0255 had a pH value of 8.14±0.10 and a calcium carbonate content of 147±10 g / kg; TMQC0256 had a pH value of 8.80±1.10 and a calcium carbonate content of 137±9 g / kg.

[0154] The ammonium chloride-ethanol exchange solution was prepared by the methods in Comparative Example 1 and Example 1 of the present invention (i.e., the pH values ​​of the ammonium chloride-ethanol exchange solution were 8.5 and 5.36, respectively), and the exchange base of the standard calcareous soil was determined according to the method in Example 1 of the present invention. Three parallel experiments were set for each sample, and the average value was taken. The results are shown in Table 5.

[0155] It can be seen from Table 5 that for the two standard soils, the exchangeability of Ca 2+ Mg 2+ , K + 、Na + There is no significant change between the measured values ​​of the content, and they are all within the standard value range. Therefore, the present invention does not need to adjust the pH of the exchange solution.

[0156] Table 5

[0157]

[0158] Experimental Example 5 Determination of exchangeable base of standard calcareous soil under conditions of salt washing and non-salting

[0159] In the analysis step 3.1 of comparative example 1, "50 mL of ethanol solution (1.1) was added, and the mixture was shaken at a frequency of 150 r / min to 180 r / min for 30 min, and then allowed to stand overnight. The soil was transferred to a funnel with filter paper, and eluted with 30 mL of ethanol solution (1.1). After the eluent was filtered dry, 30 mL of ethanol solution (1.1) was added to continue eluting, and the process was repeated several times until there was no Cl − and SO 4 2− The reaction is continued until the reaction is continued. "These operations are all salt washing processes. The salt washing step omitted in Example 1 means that this salt washing process is omitted.

[0160] Two standard calcareous soils were selected, TMQC0255 had a pH value of 8.14±0.10 and a calcium carbonate content of 147±10 g / kg; TMQC0256 had a pH value of 8.80±1.10 and a calcium carbonate content of 137±9 g / kg. The exchangeable base of the standard calcareous soil was determined under the conditions of washing salt and not washing salt using the method of Example 1 of the present invention. Three parallel experiments were set for each sample and the average value was taken. The results are shown in Table 6.

[0161] It can be seen from Table 6 that for the two standard soils, the exchangeability of Ca 2+Mg 2+ , K + 、Na + The results of the content determinations did not change significantly and were all within the standard value range. Therefore, the salt washing step can be omitted in the present invention.

[0162] Table 6

[0163]

[0164] Experimental Example 6 Determination of exchangeable base of standard calcareous soil under different exchange treatment times

[0165] Two standard calcareous soils were selected, TMQC0255 pH value was 8.14±0.10, calcium carbonate content was 147±10 g / kg; TMQC0256 pH value was 8.80±1.10, calcium carbonate content was 137±9 g / kg. The exchange base content was measured by the method of Example 1 of the present invention when the exchange treatment times were 1, 2 and 3 times, and 3 parallel experiments were set for each sample, and the average value was taken. The results are shown in Table 7.

[0166] It can be seen from Table 7 that for the two standard soils, the exchangeable Ca 2+ Mg 2+ , K + 、Na + The results of the content determinations did not change significantly and were all within the standard value range. Therefore, the present invention adopts one exchange process.

[0167] Table 7

[0168]

[0169] In summary, when determining the exchangeable base and total base amount of calcareous soil according to the NY / T 1615-2008 standard, it is necessary to add 70% ethanol solution and let it stand overnight, and to rinse the salt with 70% ethanol solution. The present invention omits these steps, and can save more than 110mL of 70% ethanol solution for washing the salt for each sample measured; the existing method needs to exchange 6 times to complete the entire exchange reaction, while the present invention only needs 1 exchange reaction, and the reaction time only needs 3min, which saves operation steps and time; the existing method needs to adjust the pH value of the exchange liquid to 8.5, while the present invention does not need to adjust, saving operation steps; the existing method needs 250mL of exchange liquid for each sample, while the present invention needs 50mL, which saves 80% of the use of ammonium chloride and 80% of the use of 70% ethanol for each sample measured compared with the corresponding method. Compared with the existing method, the present invention has the effect of significantly improving work efficiency and reducing the use of reagents.

[0170] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for determining the exchangeable base and the total amount of base in calcareous soil, characterized in that: The soil to be tested and a magnetic stirrer are placed in a centrifuge tube, and an ammonium chloride-ethanol exchange solution is added. The centrifuge tube is placed on a magnetic stirrer for magnetic stirring. During the stirring process, a vortex is maintained on the liquid surface. The stirring time is 3-5 minutes. The filtrate is filtered and collected to determine and analyze the exchangeable base and the total amount of the base. The soil to be tested is calcareous soil. The cation exchange capacity of the soil is calculated based on the difference in the ammonium ion concentration in the exchange solution before and after the exchange. The exchangeable sodium is calculated using the difference method, that is, exchangeable sodium = cation exchange capacity - (exchangeable calcium + exchangeable magnesium + exchangeable potassium).

2. The method according to claim 1, characterized in that: The calculation formula of the soil cation exchange capacity CEC is: Where: CEC—cation exchange capacity of soil sample, cmol / kg; c0—NH4 in exchange liquid + Initial concentration, mg / L; c—NH4 in the test solution + Concentration, mg / L; V—the volume of exchange solution added to each sample, mL; m—weight of air-dried sample, g; 180—per cmol NH4 + Mass, mg / cmol.

3. The method according to claim 1, characterized in that: The calculation formula for the exchangeable base and the total amount of base is: Where: ρ(Ca), ρ(Mg), ρ(K)—respectively refer to the concentration values ​​of calcium, magnesium, and potassium in the test solution obtained by checking the standard working curve or solving the regression equation, in milligrams per liter (mg / L); V—the volume of the liquid to be tested, in milliliters (mL); m—the mass of the sample weighed, in grams (g); 20.04, 12.16, 39.10—respectively calcium (1 / 2Ca 2+ )、Magnesium(1 / 2Mg 2+ ), potassium (K + ) is the numerical value of the molar mass of a substance in grams per mole (g / mol); ts—dilution multiple; 10—Conversion factor from millimole per kilogram to centimole per kilogram.

4. The method according to any one of claims 1 to 3, characterized in that: Use 50 mL of ammonium chloride-ethanol exchange solution for every 5.00 g of soil to be tested.

5. The method according to any one of claims 1 to 3, characterized in that: The depth of the vortex is 2-5 mm; and / or The magnetic stirrer is of type A.

6. The method according to any one of claims 1 to 3, characterized in that: The stirring time is 3 min.

7. The method according to any one of claims 1 to 3, characterized in that: The preparation method of each liter of the ammonium chloride-ethanol exchange solution is as follows: 5.35 g of ammonium chloride is dissolved in 70% ethanol solution and the volume is fixed to 1000 mL.

8. The method according to any one of claims 1 to 3, characterized in that: Before the soil to be tested is exchanged with the ammonium chloride-ethanol exchange solution, it is not necessary to use a 70% ethanol solution to stand overnight and rinse the salt.

9. The method according to any one of claims 1 to 3, characterized in that: When the soil to be tested is subjected to exchange reaction with the ammonium chloride-ethanol exchange solution, only one exchange treatment is required.

10. The method according to any one of claims 1 to 3, characterized in that: The filtrate collected after the filtration does not need to be constant to volume.

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