Effect of organic fertilizer and straw returning on soil surface electrochemical characteristics

Minute particles within the soil can normally possess charges and predominantly concentrate on the soil colloids. These charges on the soil surface can contribute to a variety of physical, chemical, and physiochemical characteristics of the soil. Key property parameters of soil colloidal particles can include the surface potential, surface charge density, surface electric field intensity, specific surface area, and surface charge number. The objective of this study was to investigate the impacts of prolonged utilization of organic fertilizer and straw on these electrochemical characteristics of the soil surface. Furthermore, the primary influencing factors were determined to enhance the fertility of arable land. A long-term experiment was conducted at the Shuitou experimental base in Yuncheng City, Shanxi Province since in 2007. Four treatments were set as the exclusive application of chemical fertilizer (F), a combination of organic and chemical fertilizer (MF), the integration of straw returning with chemical fertilizer (SF), and a comprehensive application of organic fertilizer, straw returning, and chemical fertilizer (MSF). The electrochemical properties of the soil surface were examined, including surface potential, surface charge density, surface electric field intensity, specific surface area, and surface charge number. Additionally, organic carbon fractions were also analyzed, such as soluble organic carbon, particulate organic carbon, mineral-associated humus, fulvic acid, and humic acid. Furthermore, the investigation was conducted on the structural characteristics of mineral-associated humus. The results indicated that the application of organic fertilizer and straw returning treatments (MF, SF, and MSF) was substantially enhanced the electrochemical characteristics of the soil surface, compared with the F treatment (P<0.05). Among them, the MSF treatment exhibited the highest values, with the respective measurements of 17.07 cmol/kg, 67.02 m²/g, 0.25 c/m², 5.12×108 V/m, and -91.14 mV, respectively. Compared with the F treatment, the MF, SF, and MSF treatments were significantly enhanced the quantities of total soil organic carbon and organic carbon fractions, including the soluble organic carbon, particulate organic carbon, mineral-associated humus, fulvic acid, and humic acid. Additionally, there was also an increase in the ratio of humic acid to fulvic acid (P<0.05). Specifically, the MSF treatment exhibited the highest contents and ratio, with the values of 21.5, 0.1, 12.1, 5.5, 3.3, 2.2 g/kg and 1.5. Meanwhile, the organic fertilizer and straw returning treatments were resulted in the a significant reduction in the E4/E6 and △lgK values of mineral-associated humus (P<0.05). There was the an increase in the relative abundance of C=O/C(O)N group within the mineral-associated humus. The comprehensive analysis revealed that there was the a significant positive correlation between soil surface electrochemical characteristics and various factors, including the total soil organic carbon, organic carbon fractions, clay content, and the ratio of humic acid to fulvic acid. Notably, there were the most substantial influences on the soil surface electrochemical characteristics by the mineral-associated humus, clay content, and the ratio of humic acid to fulvic acid, with the interpretation rates of 67.0%, 5.9%, and 4.8% respectively. And the E4/E6, △lgK, and C=O/C(O)N groups of humus were strongly associated with the soil surface electrochemical characteristics. In summary, the prolonged use of organic fertilizer and straw were substantially enhanced the electrochemical properties of the soil surface, in terms of the soil organic carbon fraction and the structural characteristics of humus. Consequently, these findings can also provide the theoretical foundation for the microscopic and macroscopic processes in soil.