SOIL FRIABILITY ASSESSMENT OF SOME AGRICULTURAL SOILS IN ROMANIA

Tensile strength is a dynamic property and is sensitive to soil structure because it is related to the presence of air-filled pores, the occurrence of micro-cracks and the strength of inter-granular bonds within and between micro-cracks. Moreover, the tensile strength of soil is much affected by the soil water content and processes which change pore characteristics and/or the cementation between structural units. A friability index has been proposed that is based on measurements of tensile strength of different sized aggregates. The main objectives of the present paper were to measure the mechanical properties (tensile strength and friability) of soil aggregates collected from three agricultural soils, and to explore the relationships between mechanical and basic physical properties of the investigated soils. Soils used in these investigations can be described as “friable” according to the classification used for friability index, F1, values. Soil aggregates of the sandy soil from Grădiștea had the smallest values of tensile strength. The highest values of tensile strength were recorded in case of clayey soil, whereas the loamy soil had values between the sandy and clayey soils. Increasing organic matter content decreased the values of tensile strength for soil aggregates from all soils. High values of clay content in case of loamy and clayey soils increased the values of tensile strength. Increasing amount of clay in sandy soil has been shown to increase the tensile strength of this soil. This may be due to clay particles acting as cementing materials between large particles. Higher amounts of clay in sandy soils provide more opportunities for interparticle contact. Small size classes of aggregates presented higher values of tensile strength as compared with larger size classes of aggregates when the volume dependence method was used. In case of sandy and clayey soils were found underestimates and respectively overestimates of F2 values. As for the loamy soil, the volume dependence method (F2) gave similar values when compared to the coefficient of variation method (F1). The coefficient of variation method is recommended as standard method for measuring soil friability.