Investigation of Soil Mechanical Resistance under Different Levels of Compaction and Cementation Treatments and the Effect of Maize and Wheat Root Development on It in Experimental Condition

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.