ehsan ghezelbash

The wetting drying cycles, through the creation of Swelling Shrinkage sequences in soil aggregates, lead to changes in the soil's microstructure. In this study, attempts were made to investigate changes in the geometric properties of loamy sand and silty clay soils by applying moisture cycles in different treatment conditions, including amendmentsand degradations. The hypothesis of this research is based on the premise that the presence of different treatment intensities of the effects of wetting drying cycles affects the soil's microstructure from the perspective of soil aggregates. Using ImageJ software, image processing was performed on 2D and 3D images acquired from soil blocks. In addition to soil aggregate volume and surface area, properties such as sphericity and flatness coefficients were estimated and used for the classification of soil aggregates. For statistical analysis and chart plotting, Orange 3 and Excel 2016 software were used. The results indicated that treatments such as calcium carbonate, cations, and organic matter increased the coefficient of soil aggregates elongation, while degradation treatments led to an increase in the coefficient of soil aggregates flatness in both studied soil textures. Geometric classification of soil aggregates revealed that a small portion of loamy sand soil aggregates were categorized as elongated soil aggregates, while more than half of them fell into the category of flatted soil aggregates. In silty clay soil samples, a uniform distribution of elongated, bladed, and flatted soil aggregates was observed. However, none of the studied treatments resulted in soil aggregates falling into the category of compacted soil. Considering the direct impact of soil aggregate shape on the hydraulic conductivity of soils, the method employed in this research can effectively determine the microstructural status of soils from the perspective of soil aggregates.

Increasing the soil mechanical resistance firstly strengthens the soil and causes its stability against external factors, and on the other hand, restricts root development and the process of root water uptake from around soil. In this study, the limitations and possible benefits of soil mechanical resistance in an optimal moisture condition were investigated. Two factors of compaction and cementation were used to increase the soil mechanical resistance at wet soil and to prevent the effects of moisture fluctuation on the initial soil mechanical resistance, a suction buffer system was used to stabilize soil moisture at the matric suction of 40 cm (aeration porosity equal to 10%). 132 experimental units at different levels of compaction (bulk densities equal to 1.52, 1.56, 1.6, 1.66, 1.69, and 1.71 Mg.m-3) and cementation (added cement equal to 0, 0.3, 0.6, 0.9, 1.2 and 1.5 percentage) treatments, maize and wheat plants were cultivated to determine the possible effect of root development on increasing the initial soil mechanical resistance. The results showed that the soil mechanical resistance increased from low to restricting values due to both compaction and cementation treatments, and a range of loose to strong soils was created due to these two treatments. Soil mechanical resistance in the control treatment and some initial levels of the two compaction and cementation treatments were in the range of loose soils, but the root development caused a significant increase in soil strength in control and compacted treatments. On the other hand, root development caused the soil limitation in terms of soil water availability to exceed the critical limit (2.5 MPa). Therefore, according to the expected function of the soil, changes in mechanical strength due to compaction, cement, and root development can be considered as an opportunity or constraint.

The complexity of the concept of soil water availability has led to the emergence of a variety of methods to estimate it, which have always been changing, refining, and replacing. Among those, the conventional method of plant available water (CPAW=FC-PWP) due to convenient measurement has received more attention. In theory, however, the methods of Integral Energy (EI) and Kirchhoff Potential (Mh0) have been considered due to the interference of soil properties and plant ability for water uptake. In this  study, the available water was calculated with CPAW, E I and Mh0 concepts in a wide range of soils (72 samples) with various physical properties and results were compared. Also, different upper limits were tested to determine the water availability and the new field capacity moisture coefficient was used as the upper limit of the concept of water availability. Despite the weak correlation between EI and Mh0, the trend of their variations in different soils is somewhat similar, indicating their similarity in the estimation of available water for plants. In contrast, the lack of a clear relationship between EI and Mh0 with CPAW confirmed their lack of correlation in explaining water availability of the plant. The convenience of using CPAW makes it even more preferable to study the variability of soils in terms of hydraulic properties. On the other hand, the use of EI and Mh0 results will be useful for explaining the available water content but still needs to be modified in terms of determining threshold limits.