Effect of different tillage systems and cover crop on aggregate stability, aggregate tensile strength and penetration resistance of a silt loam soil in Hamedan

Soil management practices have different impacts on the values of soil resistance at different suctions, which rarely have been evaluated. In this study the combined effects of tillage and cover crop factors on the aggregate stability, aggregates tensile strength and soil penetration resistance at different suctions were evaluated. The tillage factor in three methods, including moldboard plow, chisel plow and no-tillage, and cover crop factor in three types including Vetch, Lathyrus and no cover crop at the factorial design with three replications was applied. Aggregate stability was measured using wet-sieving method. Tensile strength of aggregates and penetration resistance of the undisturbed samples were determined by Dexter and Kroesbergen indirect method and a micro penetrometer, respectively. Soil management practices had the highest effect on the resistance characteristics at 30 kPa matric suction. No tillage treatment reduced tensile strength due to reduced tillage intensity and undisturbing soil. Conservation tillage with Lathyrus cover crop, increased stability of aggregates by 155 percent comparing to no tillage-no cover crop in the spring season. Also conservation tillage with Lathyrus treatment, increased tensile strength of aggregates by 7-45 percent comparing to other treatments in the autumn season. The conservation tillage without cover crop reduced penetration resistance compared to most treatments by 4.5-99 percent at most matric suctions due to reduced plowing and decreasing agricultural machinery traffic. Therefore, we recommend using Lathyrus cover crop with conservation tillage in agricultural fields. The results of studying aggregates strength, with further research, could be used to determine the optimum time of agricultural operations.