Keywords: preferential flow, temporal stability, tillage, no-tillage.

Preferential flow is considered one of the main contributory factors of the phenomenon of rapid transportation of contaminants in the vadose zone to groundwater. The existing literature indicates that soil heterogeneity and soil management practices influence preferential flow. The temporal changes of the soil moisture regimes in the vadose zone can provide useful insights into identifying the potential zones of preferential flow, which may be reflected in the temporal stability of the soil moisture regime. Therefore, it is hypothesised that the evidence of higher temporal instability in soil moisture content of a location reflects a higher potential to support preferential flow. 

Changes in soil moisture regime in two transects located on two plots with different tillage management practices, no-till and conventionally tilled, were investigated over two years using soil moisture sensors placed in a rectangular grid in each plot by measuring hourly water moisture contents during the two growing seasons.
 
 The statistical analysis of mean relative difference of daily average water content indicated high variations along some columns reflecting a greater instability of the soil moisture regimes at these locations in the plot. At locations with preferential flow, comparatively high positive relative mean differences were observed. The time stability of the soil moisture regime along the columns varied between the first half of the growing season and the remainder, type of tillage management practice adopted, the row crop, and appears to be influenced by the crop row positions in the tilled plot, while the patterns did not change considerably between the two consecutive non-growing seasons.