سید بهمن موسوی

Abstract Soil compaction in farm lands can reduce crop growth and cause environmental impacts. Regarding its durability, compaction of underlying soil can be a long-term threat to soil productivity. Therefore, it is important to provide advice to farmers on how to prevent soil compaction. In this study, four soil samples with different particle size distribution preloading of 60 kPa and 120 kPa and reloading of 0, 10, 15, 22, 34, 51, 76, 114, 171, 256, 384 and 575 kPa stresses (kPa) in 10-minute intervals in continuous mode (without release) were performed in four replications using Odometer. Finally, graphical method of Casagrande, the mathematical functions of the van Genochten- Mualem equation and logit function were used to determine the pre-compression stress. The results of analysis of variance showed that the pre-compression stress in different texture classes significantly (P≤0.01) was affected by the main effects of preloading with 60 and 120 kPa and different procedures of estimating pre-compression stress as well as their interaction effect. The highest pre-compression stress was 181.7 kPa related to the sandy loam texture class and the lowest was 59.2 kPa subjected to silt texture class. The pretreatment interactions on prediction pre-compression stress showed that pre-treatment of 120 kPa significantly increased (P≤0.01) pre-compression stress by 50% compared to pre-treatment of 60 kPa. The interaction effects of pre-compression stress estimation procedures on soil textural classes showed that van Genochten- Mualem equation procedure significantly (P≤0.01) had the highest estimate of pre-compression stress (154 kPa) compared to other procedures, while the graphical estimation method of Casagrande showed the lowest pre-compression stress (108 kPa), and the Logit function was between these two values (121 kPa). The three-way interactions between estimating procedures of pre-compression stress with pre-treatment factor and soil texture classes showed that