Identifying the characteristic scales of soil structural recovery after compaction from three in-field methods of monitoring

The impact of compaction by traffic on agricultural soils is not strict and irreversible. After compaction by machine traffic, soil structure changes both spatially and temporally as different generative processes occur. These are generally well-described in the literature. However, the preferential periods of occurrence and the soil depths affected by changes - thus, the characteristic scales of soil structural recovery - remain hypothetical. Further investigation through precise spatial and temporal monitoring under real in-field soil conditions is needed. In this paper, the structural changes of a locally trafficked silt-loam soil were assessed under both cropped and bare areas conventionally tilled from one-year soil monitoring. The monitoring was performed in-field by three methods at a low temporal resolution with the standard methods of visual description and soil coring in pits, and at a high temporal resolution with the non-destructive Electrical Resistivity Tomography (ERT) method. The specific use of ERT for this purpose is discussed. Compaction by traffic affected the overall tilled soil layer and was shown to be time-persistent. This suggested a characteristic time-scale of a complete structural recovery longer than one year, regardless of soil management. At the finest temporal scale, the results also highlighted some seasonal processes that potentially affect the long-term recovery, such as bio-drilling and soil cracking. The processes were related to the soil management, the wetting/drying cycles and the freeze/thaw effect. They likewise induced the start of structure fragmentation in the first centimetres of the soil and acted abruptly in the dry period, preferentially under the area initially cropped, with persistent effects on the soil structure in the rainy and cool season. (C) 2013 Elsevier B.V. All rights reserved.