EC, electrical conductivity; HC, hydraulic conductivity; CM, coarse material; CEC, cation exchange capacity; WY, wheat yield; SOM, soil organic matter; PR, penetration resistance.

**Table 9.** Factor analysis for subsoil in study area.

Finally, wheat yield and penetration resistance were loaded in Factor 9 and it was named as "crop yield factor". The crop yield factor described 4.46% of the total variation. Loadings showed a high negative correlation (*R*<sup>2</sup> = −0.735) between these two variables in the study area. Similar results were found elsewhere, PR reduced wheat and soybean yields [57]. Others [58] showed that PR had a highly adverse effect on wheat spike number. Results of another study [59] showed that PR was a limiting factor of soybean yield due to its adverse effect on field capacity.

In subsoil, 19 variables were grouped in seven factors that accounted for 73.2% of total variance, as shown in **Table 9**. Available Mn content, pH, and available Fe content were loaded in Factor 1, which described 16.9% of the total variation in the studied variables. Factor 1 was named as "microelement factor". The loadings showed a positive relationship among Mn, Cu, and Fe contents and a negative correlation between pH and each of these variables. The variables of clay, sand, EC, and HC were loaded in Factor 2, which described 16.2% of the total variance. Factor 2 was named as "soil physics factor". Hydraulic conductivity had a negative loading, whereas EC and clay had positive loadings in Factor 2, suggesting that contrary to sand, both clay content and EC had a negative effect on HC. Factor 3 described 10.9% of the total variance. The variables Zn and available P were loaded in this factor. Hydraulic conductivity was also loaded in this factor. Factor 4, named "soil chemistry", included CEC, Cu, and EC and described 8.3% of the total variance. Wheat yield, silt, and SOM were loaded in Factor 5, which described 7.2% of the total variance. Factor 5 was named as "yield factor". Available K and B were loaded in Factor 6, and Cd and PR were loaded in Factor 7. Factor 6, describing 6.9% of variance, was named as "soil potassium factor", and Factor 7, describing 6.7% of total variance, was named as "soil cadmium factor".
