EVALUATION OF FACTORS AFFECTING MODULUS OF RUPTURE AS AN INDEX OF CRUSTING IN SELECTED CALCAREOUS SOILS

* ASTRACT: Soil crusting influences seedling emergence, root penetration, and morphology of the shoot; consequently, crop yield is adversely affected. The objective of this experiment was to study the factors affecting modulus of rupture as an index of crusting. Fifteen surface calcareous soil samples were collected from different areas of Fars province, Iran. T heir physicochemical properties were determined and related to the simulated soil crust in the form of modulus of rupture by simple linear regression. Because soil resistance is dependent on the balance of disruptive and stabilizing factors, all parameters were added at the same time and checked by stepwise and backward methods. At the first step, both soil solution salinity (EC) and sand content showed the highest correlation with soil crust resistance (R 2 = 0.64, P≤ 0.001,). By testing multiple regressions in stepwise and backward method, more soil properties entered into the equation and the respective R 2 increased to as high as 0.87 (P≤ 0.001). In general the results of this study show that soil flocculating ag ents prevent crust hardening whereas dispersive agents lead to crust formation.