Effect of loading time on soil structural failure

Abstract

Identifying compaction potential for varying loads and soil conditions is vital for making management decisions related to crop seed germination, plant growth and crop production. However, the interacting effects of loading and loading duration on compaction related structural integrity were still unclear. Changes in soil water potential have proven to be a useful indicator for evaluating compaction induced changes in soil structure during stress application. The objective for this study was to determine the effect of load and loading time on soil structural degradation of four different soil materials with four different initial gravimetric soil water contents (11, 15, 19 and 24%). Soil structural failure was based on changes in soil water potential relative to the water potential observed for critical stress loads which are the stress associated with soil structural failure. With a fixed load of 4.0 kg/cm2, which approximates the load applied with normal field tractors used in Northeast China, soil water potential decreased with increasing loading time from 0 to 100 s for all soil material and water content combinations. For short term loading, water potential decreases were consistently found for loading times of 1 s or less across all soil materials. For all soil materials, loads applied for 0.1 s accounted for more than 50% of the water potential change that occurred during 1 s load application. Increasing soil water content not only reduced the critical stress value, but also reduced the loading time required to reach critical stress water potential. This finding demonstrates that loading time (0–1 s), approximating that of implement wheels or planter press wheels, reduces soil water potential sufficiently to affect water movement, potentially important for seed germination associated with planter press wheel operation. Additionally, loads that at least marginally exceeding the critical stress static load can be applied for a short time (0–1 s) without causing structural degradation.