The Effect of Root Systems and Plant Type on Physicochemical Quality and Soil Structure Stability Incdices

Background and objectives
Plant roots have significant effects on the soil and lead to significant changes in soil characteristics, that these changes have a great impact on soil erodibility potential, management of land and crops, and affect many known factors affecting soil such as the activity of microorganisms and tillage. Soil structure is very important due to its influence on soil health, sustainable agriculture and carbon sequestration. Considering the importance of soil structure stability in sustainable agriculture and the effect of plants with different root systems (one of the most important factors affecting soil physical properties) on soil structure stability and physicochemical characteristics, the objective of this research was to study the impact of various root systems of alfalfa, cumin, chickpeas, wheat and barley on the physical and chemical properties of the soil and in different depths of the soil.

Materials and methods
This research was performed as a randomized complete block design with three replications in the research farm of Ferdowsi University of Mashhad, Khorasan Razavi province. The plots with dimensions of 10×100 meters were managed with specific dimensions and tillage systems and based on root systems alfalfa, cumin, peas, wheat and barley plants were selected and cultivated. At the end of the growing season (harvest time), disturbed and undisturbed soil samples were collected from four depths of 0-10, 10-20, 20-30 and 30-40 cm around the plant roots. The roots of each plant were also taken. Soil samples were analyzed for chemical and physical characteristics including macro nutrients, water infiltration, and structural stability indicators. The root characteristics, including Root Length Density (RLD), were obtained by root scanning. SAS and R software were used for data analysis and Microsoft Excel was used to draw the graphs.

Results
The results revealed that the highest amount of salinity in the soil under wheat and barley cultivation (2.3 and 1.6 dS/m, respectively) was found in the soil depths of 0 to 40 cm. The soil under cumin contained the highest content of organic carbon at the depths of 0-10 and 10-20 cm (0.79 and 0.76%, respectively) and the lowest content of soil organic carbon (0.2%) at the depth of 30-40 cm. The amount of nitrogen was obtained in the soil under the chickpea plant (0-40 cm) and it was significantly higher than that of other plants, and the highest amount was found in the soil depth of 30-40 cm (0.1%). With the increase of soil depth, the amount of saturated hydraulic conductivity of the soil decreased, and the highest value was at the depth of 0-10 cm (2.44 cm/min) of the alfalfa and the lowest value was obtained at the depth of 30-40 cm (0.49 cm/min) for wheat. The highest value of soil structure stability index (2.15%) was obtained in the soil cultivated with cumin and the lowest value (0.48%) was obtained in the depth of 30-40 cm in the soil cultivated with alfalfa. The average soil stability index in all studied plants was less than 5%, which indicates the destruction of the soil structure due to the insufficient amount of organic carbon.

Conclusion
The results of this research showed that even with the same type of root system, plants have different effects on the physical and chemical characteristics of the soil. In general, the soil under cumin cultivation had the lowest salinity and the highest organic matter, consequently increased the soil structure stability index. Also, the root system of alfalfa was very effective in creating large pores and increasing the saturated hydraulic conductivity.