| At present, Chinese agriculture is transferring from traditional linear mode to circular mode.The essence of circular agriculture is the organic combination of agricultural cleaner production and waste resources utilization. Circular agriculture can achieve the overall development goals of high efficiency, low consumption and low emissions. In this study, with the guidance of recycling and utilizing waste resources, five different types of organic wastes, including maize straw(MS), cow manure(CM), chicken dung(CD), fungi dregs(FD), and leaves(LF) were applied with fertilizers for field experiment, and no fertilizer treatment(CK) and fertilizers only treatment(NPK) were chosen as control group. The focus of the study was the testing and analyzing of the dynamic changes of chemical characteristics(organic carbon, pH, cation exchange capacity and charge property), aggregate composition and stability, humus content and combining forms, composition of humus substances and humic characteristics. Elemental Analyzer, IR, NMR, TG-DTA were used to study the effects of different organic wastes on aggregation of black soil and characteristics of humus, and its mechanism. The main results and conclusions are as follows:1. Application of organic wastes increased, in varying degrees, the content of soil organic carbon, adjusted soil pH and cation exchange performance, and to some extent affected composite surface charge.Compared with CK, CM+NPK and MS+NPK treatments increased soil organic carbon content significantly. The content of exchangeable H+ and Al3+ in MS+NPK and FD+NPK treatments varied with the change of the total amount of exchangeable acid in 3 years, and the highest amount of changeable total acid content and H+appeared in CM+NPK treatment. The soil composite colloid surface charge Qsurface increased with the increase of pH. When pH>6, the curves of CM+NPK and CD+NPK treatments were similar and higher than others, MS+NPK and LF+NPK treatments were in the middle, CK and NPK treatments were similar and lower.Compared with CK, chemical fertilizers only improved the content of soil organic carbon slightly, but the pH value of the soil decreased sharply year by year and the content of soil exchangeable Ca2+and Mg2+was reduced.2. Application of organic wastes promoted the formation of soil aggregates and improved the stability of aggregates.The application of organic wastes increased the content of soil aggregates whose size was over 0.25 mm, which was beneficial to the transformation of smaller-size aggregates to larger-size aggregates, and with time, transformation range led to different results of the content of aggregates with mechanical stability and that of water-stable aggregates. The content ofaggregates with mechanical stability was mainly >5mm and the content of water-stable aggregates was mainly 1~0.5mm. MWD and GMD value of soil aggregates was in significantly positive correlation(p<0.05) with the content of aggregates whose size was >0.25 mm and in significantly negative correlation with fractal dimension D. The content of aggregates whose size was >0.25 mm was positively correlated with soil organic carbon and soil organic carbon directly affected aggregate stabilization. Soil aggregate stability was higher in CM+NPK and MS+NPK treatments, CD+NPK, FD+NPK and LF+NPK treatments also increased the stability of soil aggregates, the effects of which were significantly higher than NPK. NPK coule increase soil aggregates whose size was >0.25 mm within a narrow range, but decrease the stabilization of soil structure, which was calculated by the aggregate particle size indexes and fractal characteristics.3. Application of organic wastes increased the activity of combined forms of soil humus.The application of five kinds of organic wastes significantly increased the content of loosely combined humus in soil and the increase was year by year, MS+NPK and CM+NPK treatments made the greatest contribution, and CD+NPK、FD+NPK and LF+NPK treatments took the second place. Concurrently, wastes treatments accumulated HA and FA, and HA made the degree of aromatic condensation smaller and gradually simpler. The content of unitedly combined humus of five different types of organic wastes treatments increased in the second year and decreased in the 3rd year. The combined degree of organic matter and inorganic gel was better in the second year. The connection state humus of each treatment was similar to stabilization state humus. The connection state humus HA optical density had significant differences in the 3rd year, and among them, the HA optical density in CM+NPK and FD+NPK was smaller. No treatment showed any significantly different effects on the content of stably combined humus. The content of HA and FA was relatively stable, being less affected by fertilization. With the three years of fertilization, the loose/tight ratio of organic wastes treatments was higher than CK or NPK treatment, and the difference was significant with time.4. Application of organic wastes treatments affected soil humus compositions and structural characteristics, and the differences were significant in CM+NPK and CD+NPK treatments.Four different types of organic wastes increased the nitrogen, hydrogen and oxygen elements content of HA, and decreased the content of carbon elements. Organic wastes increased carbon and nitrogen elements content of FA and decreased the content of oxygen elements, CM+NPK and FD+NPK treatments were similar in the effects of element compositions of FA. Organic wastes treatments decreased hydrogen element content of HMi and increased oxygen element content, and at the same time, decreased hydrogen and oxygenelements content of HMc and increased carbon and nitrogen elements content of HMc. Organic materials increased soil HA aliphaticity and decreased soil HA aromaticity. The most significant treatments of soil HA aliphaticity were CM+NPK and MS+NPK; FD+NPK and LF+NPK treatments were in the middle; the most significant treatment of soil HA aromaticity was CD+NPK. NPK treatment didn’t affect the structure of HA.In summary, the returning of agricultural wastes in different cycle modes improved physical and chemical properties of soil and soil productivity. |
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