The Effect of Different Na/K Ratios in Soil Solution on Aggregate Tensile Strength and Friability

This research was carried out to study the effect of different ratio of Na/K in soil solution on dispersible clay, aggregate tensile strength and soil friability using the cation ratio of soil structural stability (CROSS) index. In order to apply different potassium concentrations, 6 treatments with the same EC (3 dS m-1) including 0 to 27.2 meqL-1 K and another six treatments with EC=6 dS m-1 including 0 to 54.4 meqL-1 K were prepared and added to soil. Soil friability was calculated and compared through two methods i.e. the coefficient of variation (F1) and ranking order (F2). The results showed that increasing the K concentration in treatments relative to Na could increase the water dispersible clay. Also, the results of aggregates tensile strength test showed that in treatments with EC=3 dS m-1 by increasing the K value, the soil strength decreased but with increasing the SAR value, soil strength increased. Maximum amount of tensile strength (142 kPa) was observed in treatment 1 with CROSS = 25.7 and SAR=22.9 and the minimum amount (87 kPa) was in treatment 5 with CROSS=14.8 and SAR=0.99. This trend was not observed in treatments with EC=6 dS m-1 and the aggregate tensile strengths were almost similar in all treatments. The results demonstrated that soil friability (F1 & F2) increased with increasing the dispersible clay at EC=3. Comparison of the results of tensile strength and friability revealed that F1 was inappropriate parameter for expression of soil friability while F2 showed the good agreement with the strength and friability amounts (in treatments with EC=3). In treatments with EC=6, the effect of dispersible clay on tensile strength and friability was not observed, probably due to the higher concentration of the soil solution.