| Soil structure controls the storage and transport of soil water and nutrients and gas diffusion, and regulating soil microbial activity, thus determining the ecological service function of the soil. Agricultural restoration practices influence soil fertility by regulating soil structure, but relevant knowledge were mainly from observations on mature soil, we were unable to locate reports about the effects of agricultural practices on changes in soil structure at the initial stages of soil development. The hypothesis of this study is that tillage and soil organic amendment can expedite the initial process of soil formation and formation of soil structure, thereby resulting in discrepancy of soil pore structural properties among different treatments. Consequently, this study simulated soil-forming process of Mollisol parent material, making use of 8 year long-term location experiment established at Chinese Academy of Sciences’ the State Key Experimental Station of Agroecology, Hailun, utilizing micro-computed tomography technology to quantify soil structural properties, accompanied by BET nitrogen adsorption method and pressure film method, discussing: 1)soil organic matter and aggregate stability; 2) soil pore distribution; 3) difference of quantitative methods of pores, to assess the effect of agricultural restoration practices on soil structural properties of Entisol. Field treatments consisted of no-tilled vegetation restoration under natural fallow(Nat F) and anthropogenic planting of alfalfa(Alfa) and soil tillage under the same cropping system with different combinations of mineral fertilization(F) and organic(C) amendment into soil,(F0C0,F1C0,F1C1,F1C2); and established two controls(parent material, PM; and Mollisol,MO). Main results as followed:(1)Undergoing 8 year field experiment, compared with PM, soil physical and chemical properties, soil organic carbon(SOC) and soil aggregate stability were improved from all field treatments, with decreasing in cation exchange capacity(CEC) of F1C1 and F1C2; the gap between field treatments and MO remains and reduces. Compared with no-tilled soils, tillage decreased soil bulk density(SBD) and aggregate stability; Alfalfa straw mulching and straw amendment increased SOC content and soil total nitrogen concentration, decreased SBD, and enhanced soil aggregate stability. In the initial process of soil formation of Mollisol parent material, the mechanism of aggregate stability was different from MO’s. Entisol in the stage of soil formation relied on young organic matter as cement to stabilize aggregates, while muture Mollisol stabilized aggregates by highly humified organic matter.(2)The effects of agricultural restoration practices on adsorption pore properties of soil aggregates, highlighted that specific surface area(SSA), total volume, 2~50 nm and <2 nm pores of filed treatments decreased; organic matter increasing reduced SSA and the porosity of pores(<2 nm).The effects on aggregate micromorphology, reflected in that the internal of aggregates from experimental treatments became loose and porous, and the connectivity and complexity of three dimensional(3D) pore structure were enhanced. The soils from field tratments were close to MO’s in two dimensional plane and three dimensional structure. Tillage increased small pores and complicated 3D structure; organic matter reduced small pores and simplified 3D structure.The effects on pore structural properties of aggregates(3-5 mm) based on CT image analysis, manifested in that total porosity, porosity of pores(>30 μm) and the amount of pores from field treatments increased.Tillage with fertilization increased porosity of pores <100 μm and soil pore connectivity; organic matter reduced pore continuity and simplified pore structure.(3)The effects of agricultural practices on pore structural properties of intact soil cores(50 mm in diameter, the same below), reflected in that in the pore derived from soil water retention curve, between no-tilled treatments, organic matter increased the porosity of pores >150 μm and 0.2~1 μm from intact soils and decreased the porosity of pores 30~150 μm and <0.2 μm; compared no-tilled soils with the tilled soils with no organic amendment, tillage decreased porosity of pores in the range of 30~150 μm, while increased the porosity of pores in the range of 0.2~30 μm. Among the tilled soils, organic amendment increased the porosity of pores 30~150 μm, and decreased the porosity of pores in the range of 0.2~30 μm.The effects on intact soil micromorphology, embodied in that compared with no-tilled soils, tilled soils became loose and porous, soil blocks were broke into secondary aggregates, increased secondary large pores by destroying large pores with homogeneous distribution; Due to a great deal of pores in intact soil, there were no difference on 3D visualization of intact soil micromorphology among field treatments.The effects on intact soil pore structural properties based on CT image analysis, reflected in that under the same cropping system, mineral fertilization led to soil crust, creating large fissures(>5000 μm) and decreasing secondary macropores(500~5000 μm); Organic amendment increased the total porosity and the porosity of pores 500~5000 μm and decreased the porosity of pores >5000 μm. Tillage with organic amendment decreased pore continuity and tortuosity, increased pore connectivity and simplified intact soil pore structure.(4)Combining CT image analyses under different resolution and scales to evaluate soil structure could be regarded as a approach to evaluate soil macropore system. Pore continuity, connectivity and volume of intact soil were dramatically larger than those of aggregates, while pore channels in soil aggregates were more tortuous than those in intact soil cores. Organic matter increasing under the tillage decreased pore continuity and increased intact soil pore connectivity; fertilisation under the tillage increased pore connectivity of soil aggregates. |
