TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Method: The method comprises:(A) crushing agricultural organic wastes, and adjusting carbon/nitrogen digestibility to 25-30, water content to 55-60%, and organic content to 60-70%;(B) composting and reacting mixture of fresh compost sample and organic chelating agent at 70-90 degrees C for 30-40 minutes;(C) adding sodium pyrophosphate solution into mixed solution to obtain 0.1 M sodium pyrophosphate in mixed solution;(D) supplying nitrogen for 5 minutes and sealing;(E) oscillating for 4 hours and allowing to stand for a night;(F) extracting after high-speed centrifugation, filtering supernatant fluid in filtering membrane having aperture of less than or equal to 0.45 mu m to obtain mixed solution of humic acid, and measuring carbon content of extract solution;(G) calculating carbon content of humus in each gram of dry compost sample based on water content of fresh sample, and absorbing extract solution;(H) adjusting pH to 1-2 using 6.0 mol/L HCl at 70-90 degrees C for 30-40 minutes;(I) separating humic acid from fulvic acid, allowing solution to stand for a night, centrifuging at high speed to separate deposit from supernatant liquid, and measuring carbon content of supernatant liquid;(J) calculating carbon content of fulvic acid in each gram of dry compost sample to determine carbon content of humic acid based on difference between carbon content of fulvic acid and that of humic acid;(K) depositing humic acid crude product, and dissolving crude product in 0.1 M sodium pyrophosphate solution;(L) adjusting solid-liquid weight ratio to 1:30, oscillating for 4 hours, allowing to stand for a night, and centrifuging at high speed to remove residue;(M) adjusting pH to 1-2 using 6.0 mol/L HCl, keeping temperature at 70-90 degrees C for 30-40 minutes, separating humic acid from fulvic acid, and allowing solution to stand for a night;(N) centrifuging at high speed to separate deposit and repeating step for 3-4 times to continually purify deposit, adding 0.1 mol/L HCl and 0.3 mol/L HF mixed solution to deposit to remove silicic acid;(O) adjusting weight ratio of deposit to 1:30, oscillating for 4 hours, centrifuging at high speed to separate deposit, washing deposit for 3-4 times, and washing deposit by deionized water to remove chloride ion in supernatant fluid; and(P) freezing and drying to obtain black humic acid crystal.Preferred Components: The agricultural organic wastes comprise vegetable leaves, straws, weeds, fallen leaves, and waste, which are rich cellulose, semicellulose and lignin. Preferred Composition: The organic chelating agent comprises mixture of gluconic acid or tartaric acid and EDTA in weight ratio of 2-3:1. The fresh compost sample and organic chelating agent are in weight ratio of 1:0.2-0.3. The weight ratio of fresh sample and water is 1:5.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Component: A total organic carbon analyzer is used for measuring carbon content.