High resolution magnetic survey for soil monitoring: detection of drainage and soil tillage effects

This paper presents the results of high resolution magnetic cartography realized with a caesium vapor magnetometer on marshland plots in Western France. This site is interesting because of the clayey substratum homogeneity and the historical knowledge of plot exploitation. A wooden truck running on PVC rails allowed acquisition of accurate signals with dynamics of about 2 nT. Natural grassland presents weak decametric variations correlated to a micro-toposequence. Conversely, plots recently tilled show linear magnetic anomalies. These anomalies are interpreted as the effect of tractor tyre soil compaction which modify soil properties. In addition, the study of a drained plot, by a wavelet transform, reveals the presence of a frequency band close to the drain intervals. Moreover, the magnitude of the linear magnetic anomalies is higher above drains. This suggests that the compaction influence on the magnetic carriers is more important in drained, hence aerated, zones.