Effects of manure/biological agent-straw strip mixing on the composition of organo-inorganic complexes and characteristics of organic carbon distribution in black soil

Strip fertilization was conducted in the black soil area of Yushu City, Jilin Province, in April 2020 according to the principle of equal carbon to explore the composition and distribution characteristics of organo-inorganic complexes in black soil under the mixed application of corn straw and livestock manure/microbial agent strips returning to the field. In the second year, the strip was changed to a planting strip without fertilization. After the straw was crushed in situ, it on the next crop sowing row was stacked towards the fallow zone on both sides to form a straw-covering strip, and two consecutive years of in situ straw-returning experiments were conducted. This experiment included four treatments: strip straw cover + chicken manure (SO), strip straw cover + cow manure (SN), strip straw cover + biological agent (SJ), and strip straw cover (SCK). Organo-inorganic complexes were extracted using the gel-dispersion grouping method and divided into aqueous (G0), sodium (G1), and ultrasonic (G2) dispersion groups. The results showed that adding animal manure and biological agents increased the soil component complexes and their carbon content compared to SCK, with the highest increases of G0 observed under the SJ treatment in 2022 at 38 g∙kg⁻¹ and 1.74 g∙kg⁻¹, respectively. In 2021, among the treatments of animal manure and biological agents, the G1 complex content under the SJ and SO treatments significantly increased by 33.46–37.66 g∙kg⁻¹ compared to that under the SN treatment, and the organic carbon content increased by 0.69–0.78 g∙kg⁻¹. The organic carbon content of the G2 complex under SJ and SO treatments showed significant differences compared to that under SN treatment. In 2022, among the animal manure and bacterial agent treatments, the carbon content of the G0 complex under SJ and SO treatments increased significantly compared to that under SN treatments, with the highest increase being 1.02 g∙kg⁻¹. The content of the G1 complex under SJ treatment significantly increased by 41.25 g∙kg⁻¹ and 49.92 g∙kg⁻¹ compared to that under SO and SN treatments, respectively. The SJ treatment showed the highest organic carbon content in the G2 complex. Between two years, the content of the G0 complex under SJ treatment increased by 23.35–23.74 g∙kg⁻¹ compared to that under SO treatment. Scanning electron microscope and X-ray diffraction phase analysis showed that the mixed application of manure/biological agent straw effectively maintained the surface structure of the complexes and improved the organic carbon conversion rate. In summary, applying corn straw mixed with biological agents is more conducive to improving soil fertility and enhancing soil carbon sequestration and can be selected as the optimal returning mode.