Assessing Soil Physical Health in Sanjaabi Plain of Kermanshah Province Using Soil Quality Indices by the Method of Principal Components Analysis

Soil compaction is one of the worst signs of soil physical collapse, which has multiple effects on reducing its physical quality. On the other hand, parameters such as aggregate stability, bulk density, hydraulic conductivity and porosity, which are the most important indicators of soil physical quality, are usually more vulnerable to improper management due to the environmental conditions of arid and semi-arid areas. In recent decades, due to not being in tune with new technology, farmers have turned to more use of machines and agricultural chemicals in order to increase production.  One of the consequences of improper land management is the compaction of the bottom layer of the plowing depth, which can be seen in almost every part of the land in Kermanshah province in recent years. This study was done as a first step in investigating this problem.

Sanjaabi plain of Kermanshah with an area of about 67,000 hectares was considered as the study area. The number of 102 points was determined by a simple systematic method. Disturbed samples were taken from the two surface layers and the bottom of the plow, as well as undisturbed samples were taken by metal cylinders from the depth of the plow pan. After Laboratory analyses, the aggregate stability was checked in both dry and wet conditions. Statistical analysis was determined using SPSS statistical software. The correlation coefficient was obtained by the Pearson method along with the correlation test. Cumulative quality indices (IQI) and Nemoro quality indices (NQI) were obtained in two collections of total data (TDS) and minimum data (MDS) through the method of principal component analysis (PCA). Then, variography and zoning of soil quality indicators were done for the spatial evaluation of soil quality using kriging method.

In the surface layer and bottom of the plow, 10 and 8 principal components were able to estimate 85.02 and 80.18 percent of the total variance, respectively. The IQI correlation coefficient of the total data set with the minimum data set in the surface layer and bottom of the plow were 0.76 and 0.61, respectively, and the Nemoro index was 0.72 and 0.58 respectively. A spherical model was fitted to all the soil quality indicators in two minimum and total data sets in two surface layers of the soil and the bottom of the plow and showed a strong spatial correlation. The parts from the north to the northwest as well as the northeast of the region had higher quality soil. Other parts of the region have low to medium quality soil due to heavy tillage, reduction of organic matter, reduction of stability of aggregate and then increase of bulk density and soil compaction.

In general, the nature of the soil, due to the decisive effect of the parent materials, has caused a uniform type, which was evident in the texture, calcareousness and mineralogy of the clay part. Continuous and intensive agricultural operations have fueled this uniformity. In the areas with high amounts of clay in the surface layer of the soil, due to the flocculating of clay and organic matter and the subsequent increase in the aggregate stability, the quality of the soil was more suitable. But in the bottom of the plow, continuous cultivation in the region has caused the soil to become even more dense due to the low amounts of organic carbon and high amounts of clay. The results of the correlation studies showed that MDS can be used with acceptable reliability instead of TDS in the soil quality assessment in the two layers of the surface and bottom of the plow. This confidence was less in the plowing bottom, which is probably due to the excessive destruction of the soil structure as a result of its compaction and homogenization.