The Different Agricultural Use Effect on Soil Evolution in Shurgol Region of Bonab

Soil characteristics and development are influenced by environmental factors such as land use. Investigating the agricultural use effect on soil development and evolution can be useful in maintaining and improving the quality of land resources and preventing soil erosion and degradation. Soil development and evolution are the result of changes in its physical, chemical, biological, morphological, micromorphological and mineralogical characteristics, so the study of soil evolution indices indicates the impact of soil on environmental factors. Various morphological, physicochemical, and micromorphological indices of soil evolution due to their special nature show different aspects of soil impact from environmental factors. Therefore, the study of soil evolution as a result of environmental conditions of its formation and development can provide a suitable perspective for the continuation or the need to change the current management to maintain or improve land quality. This research study intends to examine the various indices of soil evolution that consider each aspect of soil development and evolution in relation to land management to be a fundamental step for the sustainable management of agricultural land.

The study area is the cultivated lands of alfalfa, corn, onion and wheat, and the adjacent barren lands in the Shurgol section of Bonab city of East Azerbaijan province, which is the site of selected control soil profiles under constant and uniform management over an average period of 15 years. After selection, the soil profiles were dug and described, and disturbed and undisturbed samples were taken from genetic horizons for physicochemical and micromorphological analyses and were transferred to the laboratory. Soils were identified and classified according to field studies and the results of laboratory analysis based on 12th edition of the Keys to Soil Taxonomy. Micromorphological studies of thin sections prepared from undisturbed soil samples were performed using a polarizing microscope based on a standard terminology system. In this study, a set of soil evolution indices, including harden, clay accumulation, appearance cation exchange capacity, MISODI, MISECA, and revised MISECA were used. Harden index is obtained by comparing the characteristics of texture class, plasticity, adhesion, type and degree of structure development, dry and wet stability of aggregates, clay coatings, darkening, lightening color and acidity of soil solum with C horizon. Clay aggregation and the apparent cation exchange capacity indices have been calculated based on the differences between the amount of soil clay in horizons B and C and the ratio of soil CEC to the percentage of clay, respectively.
To calculate the MISODI, MISECA and revised MISECA indices, the studied pedofeatures during micromorphological analyses, including microstructure, b- fabric, coating, nodule and degree of weathering and evolution of mineral particles were used. For this purpose, each of the mentioned characteristics, in terms of quality and quantity, was assigned a weight based on the relevant scoring tables, and the final evolution index was calculated from all of them.

The results showed that the soils of the region are non-saline and pH neutral; their texture is clay loam to clay and different amounts of organic carbon with irregular depth distribution are observed in soils under each type of productivity. Based on a complete study of the characteristics, different families of Inceptisols were identified with cambic and calcic horizons characteristic as well as Vertic properties in the soils of the region. Micromorphological studies revealed that the voids are simple and compound packing and include channels with granular and blocky microstructure in the surface horizons as well as chamber and sometimes vugh with massive microstructure in the lower horizons, while in the middle horizons angular blocky and subangular blocky microstructure were observed. According to the boundary between fine and coarse particles with 20 microns dimensions, the c/f particles in all soils have increased from surface to depth and the coarse part includes a variety of minerals. The b-fabric and related distribution pattern between the predominant coarse particles are of the crystalline and porphyric types, which in some cases are observed in speckled and monic forms, respectively. Pedofeatures observed in the soils of the region include intact, semi-decomposed and fully-decomposed organic residues, partial clay coatings and continuous and incomplete lime coatings and infillings in the channel. Soils under alfalfa productivity type with values ​​of 26.98, 1345.83, 13, 15 and 16 were identified as the most complete soils for harden, clay accumulation, MISODI, MISECA and revised MISECA soil evolution indices, respectively, while barren soils with 15.52, 419.75, 7,8 and 8 were identified as the least developed soils for the mentioned indices and the evolutionary order between these two groups is based on the mentioned indices for the productivity types of corn, onion and wheat. The values for the appearance cation exchange capacity index were 0.7 for wheat and barren soils, 0.68 for corn and onion and 0.67 for alfalfa.

As for soil classification, although differences exist at different categories or levels, but in this study, even at the family category or level, it is not possible to express the differences between soils under the productivity types of corn, onion, wheat and barren lands. In such cases, it can be useful to consider the soil evolution indices that quantitatively examine soil properties and determine their differences. Soil properties and, consequently, their evolution are affected by the productivity type in agricultural uses, and among these properties, the ones related to soil fabric are affected more than the others. Observing the evolutionary order of the majority of soils based on the studied indices for the productivity types of alfalfa, corn, onion, wheat and barren lands indicates that optimal agricultural operations and sustainable land use lead to accelerated evolution. Based on the quantitative values obtained for different indices in different types of productivity, it can be stated that the effectiveness of soils from the cultivated crop depends on the morphological and physiological characteristics of the plant and their planting, holding, and harvesting operations. Therefore, in arid and semi-arid areas, such as the studied area, where the soils are young and at the beginning of their evolution, the existence of more complete soils will be in line with increasing their quality and will prevent land degradation.