Characterization And Quantification Of Soil Aggregate Stability And Pore Structure

Soil physical barrier factor is the one main obstacle to the agricultural production. It limits the crop root outspread, reduces the soil resistance and severely restricts the sustainable development of agricultural production. This paper deals with the occurrence, damage mechanism, the amendment technology of soil with poor physical properties. The main results obtained were as follows:1. The aggregate size distribution (ASD) of Vertisols determined by dry-wet-sieving methods showed that the soils were made up>5mm and1-0.5mm aggregates. The mean weight diameter (MWD) determined by Le Bissonnais method indicated that the MWD was ranked in the following order:fast wetting>slow wetting>wet-stirring, implying the slaking of the aggregate plays an important role in aggregate breakdown. The entrapped air and differential swelling of clay minerals in aggregate resulted in aggregate breakdown.2. The pore size distribution of soils was determined by nitrogen adsorption and mercury intrusion porosimetry (MIP). The differential pore curve of clayey soils measured by MIP exhibited three distinct peaks in pore regions that ranged from60to100μm,0.3to0.4μm and0.009to0.012μm along the entire range of investigated pores (0.003-360μm). In clayey soils, ultramicroporosity (0.1-5μm) was the main pore class calculated by MIP (on average35.5%), followed by macropores (31.4%), cryptopores (16.0%), micropores (9.7%) and mesopores (7.3%), respectively. The pore structure charateristics and PSD of clayey soils is largerly influenced by soil organic matter (OM) removal. Soil OM removal reduced the pore volume and porosity of5-100μm diameter in the clayey soils, which resulted in increase of smaller pores (<0.5μm) in both5-2and2-0.25mm aggregates. The increase of microporosity may be caused by a process of disaggregation and partial emptying of small pores after destruction of organic matter.3. The influence of soil amendments (biochar and coal fly ash) on the physical quality was evaluated by aggregate size distribution and stability, water retention, and pore space structure of biochar-amended soils. The straw biochar and wastewater sludge biochar significantly enhanced the formation of5-2mm and0.25-0.5mm aggregates, and decreased the amount of microaggregate in the biochar-amended soil. The application of straw biochar significantly increased pore volume in the macropore (>75μm) and mesopore (30-75μm) ranges, which may be the result of the reorganization of pore size distribution and aggregation processes induced by the addition of biochar. Results indicated that biochar had the potential to improve the physical quality and pore space status of clayey soil. It is suggested that biochar may be considered as a soil amendment for improving poor physical characteristics of clayey soil.