Abstract:【Objective】 The aggregation of soil colloids is closely related to the formation of soil aggregates. Fertilization can change the environment of soil solution, and affect the formation of soil aggregates, soil structure and soil mineral composition. It is necessary to explore the relationship between the long-term effects of different fertilization on the microscopic properties and interactions of soil colloids and thus the macroscopic phenomena of soils. 【Method】 Based on a 35-year long-term fertilization monitoring experiment in the experimental station of brown earth, soils treated with no fertilization(CK), nitrogen fertilizer(N), organic fertilizer(M) and the combination of nitrogen fertilizer and organic fertilizer(N+M) were selected as the research objects in this study. Dynamic light scattering technology was used to monitor the dynamic aggregation process of soil colloids with different fertilization treatments. The effects of fertilization treatments on colloid aggregation were comparatively analyzed through the organic matter content, soil mineral composition and surface chemical properties. 【Result】 The soil colloids of the four treatments showed the characteristics of slow aggregation(RLCA) at low electrolyte concentration and fast aggregation(DLCA) at high electrolyte concentration. The order of critical coagulation concentration of four different fertilization treatments was M > N+M > CK > N. Also the long-term application of organic fertilizer increased soil organic matter, thereby increasing the electric field strength near the surface of colloidal particles and the electrostatic repulsion between colloidal particles. Furthermore, the steric hindrance effects of humus weakened the phenomenon of colloid aggregation; On the other hand, long-term fertilization did not change the soil clay mineral composition type, but had an impact on its relative content. The application of organic fertilizer increased the relative content of 2:1 type illite and decreased the relative content of 1:1 type kaolinite. The application of nitrogen fertilizer reduced the relative content of illite and increased the relative content of kaolinite. 【Conclusion】 Different fertilization treatments for a long time changed the basic physicochemical properties and mineral composition ratio of brown earth colloids, which in turn affected the aggregation kinetics of brown earth colloids.

Abstract:【Objective】Soil nanoparticles are organic-mineral complexes. It is of great practical significance to study stability of the suspension of natural soil nanoparticles. However, so far little attention has been paid to effect of organic-mineral complexes on stability of soil nanoparticles, and let alone its mechanism. 【Method】 In this study soil nanoparticles were extracted, separately, from soil samples of Lou soil and cinnamon soil before and after soil organic matter was removed with the aid of the ultrasonic dispersion method and the Stokes’ law based high-speed centrifugation method for analysis of particle size distribution, zeta potential, critical coagulation concentration (CCC) in NaCl and CaCl2 solutions and characterized with the dynamic light scattering technique. Furthermore, Hamaker constants of and interaction energies between the soil nanoparticles were calcuated in line with the DLVO (Derjauin-Landau-Verwey-Overbeek) theory, mechanism of organic matter removal affecting stability of soil nanoparticle suspensions explored and role of organic-mineral complexation in stabilizing soil aggregates explained. 【Result】 Results show that the Lou and cinnamon soil nanoparticles were 94.00 nm and 88.20 nm, respectively, in average diameter and the OMR (organic matter removed) loess nanoparticles slightly higher than 100 nm; the obtained loess nanoparticles were all of the polydisperse system and quite approximate to each other in ploydispersity. The nanoparticles in the all the four types of loess soil samples carried negative charge on the surface and their zeta potential increased with rising pH of the solution in absolute value due to deprotonation of the functional groups on the surface of the organic matter. As the soils varied in clay mineral property, the nanoparticles in the cinnamon soil varied more sharply in surface zeta potential than those of the Lou soil; the cinnamon soil contained more variably-charged kaolinite, while the Lou soil contained more permanently-charged illite. The functional groups on the surface of organic matter, like alcoholic hydroxyl, phenolic hydroxyl and carboxyl, are the main sources of soil negative charges. Compared with the nanoparticles in the Lou and cinnamon soils, those in the OMR Lou and cinnamon were lower in absolute value of the zeta potential as they were lower in organic organic matter. The nanoparticles in the Lou and cinamon soils were 1.70 mmol·L-1 and 1.51 mmol·L-1, respectively, in CCC while those in the OMR Lou and cinnamon soils were 10.58 mmol·L-1 and 11.69 mmol·L-1; Obviously, removal of organic matter enhanced stability of the nanoparticle suspension. Based on DLVO-based simulation, the nanoparticles in the Lou and cinnamon soils in vacuum were 6.86 × 10-20 J and 9.73 × 10-20 J, in Hamaker constant and those in the OMR Lou and cinnamon soils were only 3.14 × 10-20 J and 3.40 × 10-20 J. Apparently, the Hamaker constants of the latters were lower than the formers and so were their van der Waals attractive potential energies. Lower absolute values of the zeta potentials of the nanoparticles in the OMR loess soils resulted in reduced electrostatic repulsive potential energies. Therefore, the removal of organic matter reduced both the van der Waals attractive potential energies and electrostatic repulsive potential energies of the nanoparticles in the loess soils. But the decrements in van der Waals attractive potential energy were higher in magnitue than those in electrostatic repulsive potential energy. Further calculations demonstrate that the nanoparticles in the OMR loess soils were higher in total potential energy than those in the Lou and cinnamon soils, which resulted in higher CCCs and higher dispersion stability of the suspensions. 【Conclusion】 The presence of organic matter affects stability of the nanoparticles in loess soils through adjusting both attractive and repulsive potential energies. The complexation of organic-mineral alters soil nanoparticle composition, which in turn determined their Hamaker constant. Removal of organic matter reduces Hamaker constants of the nanoparticles in loess, leading to low attractive potential energy between nanoparticles in OMR Lou and cinnamon soil. Therefore, it is concluded that organic-mineral complexation may enhance stability of soil aggregates through increasing Hamaker constant.