The method for measuring soil nutrients in Kyrgyzstan is extended to the method of the former Soviet Union and has been revised many times during its application. China's Xinjiang soil nutrient measurement method is based on Xinjiang local standards suitable for Xinjiang regional soil based on national standards. 1. Comparison of soil measurement methods The collected soil samples were evenly mixed and divided into 2 parts according to the quartering method. One part was tested for nutrient content in the laboratory of Kyrgyzstan State Agricultural University; the other part was tested for nutrient content in the State Key Laboratory of Desert and Oasis Ecology, Institute of Soil Fertilizer and Agricultural Water Saving, Xinjiang Academy of Agricultural Sciences. The two countries used different methods to repeat the measurements three times to take the average value, and the measurement results were compared, analyzed and discussed. (1) Kyrgyzstan. Hydrogenation hot potassium dichromate oxidation method-colorimetric method: Take a 0.2000 g soil sample through a 0.1 mm sieve, put it into a 50-mL Erlenmeyer flask, add 10 mL of potassium dichromate concentrated sulfuric acid mixed liquid, mix well, stand for 20 minutes, add 10 mL of water, shake well, let stand or overnight, suck 3 mL of the supernatant into a 10-mL colorimetric tube, add water to scale, and shake well. Use a 1 cm optical diameter cuvette at a wavelength of 590 nm to measure the absorbance value with a reagent blank zeroing, and take glucose solutions with varying carbon mass concentrations of 5 g/L as standard solutions to make a standard curve. See the formula for calculation of soil organic matter content:

Where: WOM-soil organic matter mass fraction;m1-soil sample carbon content (mg) determined from the standard curve;m-soil sample mass (g);1.32-oxidation correction coefficient;1.724-organic carbon conversion organic matter coefficient. (2) Xinjiang, China. High temperature external heat potassium dichromate oxidation method-volumetric method (Xinjiang local standard DB/6500B11 1440-87), accurately weigh 0.100~0.500 g of air-dried soil sample that passes through a 0.25 mm sieve, add 5 mL of potassium dichromate and concentrated sulfuric acid each, thoroughly mix, and heat under constant temperature conditions.(Boiling at a constant temperature of 180℃ for 5 minutes), use a certain amount of standard potassium dichromate-sulfuric acid solution to oxidize soil organic matter (oxidation degree is 90%), use standard ferrous sulfate solution to titrate excess potassium dichromate, calculate the organic carbon content from the amount of potassium dichromate consumed, and multiply it by 1.724 (empirical constant for conversion of organic carbon into organic matter) and 1.1 (method correction coefficient) to obtain the soil organic matter content. See the formula for calculation of soil organic matter content:

Where: WOM-the mass fraction of organic matter in the soil;V0-the number of FeSO4 milliliters used when titrating the blank;V-the number of FeSO4 milliliters used when titrating the soil sample;V1-the number of K2Cr2O7 used; The concentration of C-1/6K2Cr2O7 standard solution;0.003-the millimole mass of carbon 0.012 is divided by the number of electrons gained and lost in the reaction 4 to get 0.003;1.724-The average carbon content of organic matter is 58%. Therefore, the measured coefficient for carbon conversion into organic matter is 100/58≈1.724;1.1-correction coefficient; and M-dried soil mass. 2. Determination method of soil total nitrogen (1) Kyrgyzstan. For Nessler colorimetric method, weigh 1.0000 g of a sample of 0.25 mm air-dried and sifted, add 5 mL of mixed acid of concentrated sulfuric acid: hydrochloric acid (10:1), place it in the refrigerator for 30 minutes, and then boil it until colorless. If necessary, add 3~5 drops of hydrochloric acid, and make the volume to 250 mL after completion. Pipet 5 mL of liquid into a 100-mL volumetric flask, add 40 mL of distilled water, add 2 mL of iron salt, stir fully, then adjust the pH with 5% NaOH through red litmus paper, add 2 mL of Nesselot reagent, and use spectrophotometer at 440 nm. Conduct color measurement. At the same time, a standard curve of nitrogen was made to calculate the total nitrogen content of the soil. See the formula for calculation of soil total nitrogen:

Where: WN-soil total nitrogen mass fraction;V-color solution volume (mL);ts-fraction multiple;m-soil mass (g). (2) Xinjiang, China. For Kjeldahl nitrogen determination method, 1.5 g of soil sample (accurate to 0.001 g) is placed in a 50-mL digestive tube, 2 g of accelerator (potassium sulfate: copper sulfate pentahydrate = 10:1 and 5 mL of concentrated sulfuric acid, and then the sample and blank reagent are placed on a far infrared digestion furnace for digestion until the soil solution is transparent blue-green or off-white (light color). After the solution cools, make the volume to 50 mL, shake well, and filter. Take 25 mL of boiling solution of soil samples into a Kjeldahl flask, and quickly add 20 mL of NaOH(10 mol/L) to the Kjeldahl flask, then add steam into the Kjeldahl flask. When the effluent is collected in the triangular flask reaches about 100 mL, remove the triangular flask, titrate the effluent with H2SO4 with a concentration of 0.001 mol/L, and read the volume of H2SO4 consumed. See the formula for calculation of soil total nitrogen:

Where: WN-mass fraction of total nitrogen in soil;V-volume of acid consumed when titrating 25 mL of solution to be tested (mL);V0-volume of acid consumed when titrating blank solution (mL);C-concentration of sulfuric acid standard solution (mol/L);m-soil mass (g);0.014-molar mass of nitrogen (kg/mol).

1. Regression equation and conversion coefficient between soil organic matter and soil total nitrogen It can be seen from Figure 1 and Table 2 that the correlation coefficient R2 between soil organic matter and total nitrogen content under different measurement methods has reached a very significant level, indicating that there is a significant positive linear correlation between soil organic matter content and soil total nitrogen content. It can be seen that the approximate content of soil total nitrogen can be estimated from the organic matter content of soil. The conversion coefficients obtained by the two test methods are basically the same, indicating that the two methods can be used in Kyrgyzstan and Xinjiang in China. The conversion factor between organic matter content and total nitrogen content is the total nitrogen content divided by the organic matter content.

It can be seen from Table 2 that soil total nitrogen (g/kg) ≈ soil organic matter (g/kg)×0.05, and the ratio of total soil total nitrogen to soil organic matter content changes with the environmental factors and utilization status of the soil. Overall, soil organic matter generally contains about 5% nitrogen.

2. Analysis of the measurement results of soil total nitrogen and organic matter The classic potassium dichromate-volumetric method is mostly used for the determination of soil organic matter, while the potassium dichromate-colorimetric method is often used in Kyrgyzstan. This method is also used in China, and its method principles are basically the same. It can be seen from Figure 2 that the measurement data of the two methods used for testing organic matter and total nitrogen have a very significant linear positive correlation, with the correlation coefficients (R2) of 0.9788 and 0.9583 respectively, indicating that the test methods used in Xinjiang, China and Kyrgyzstan have good reproducibility, that is, the measurement data have high consistency.