Intraseasonal dynamics of soil moisture variability within a small agricultural maize cropped field

The spatio-temporal dynamics of soil water content was investigated within a small agricultural maize cropped field located in Belgium. Soil moisture measurements were intensively, made between May, 30 and September 13. 1999 on 28 sampling locations at different depths (from 0 to 125 cm) with both TDR and neutron probe. The adopted sampling scheme resulted in a comprehensive data set of nearly 8000 soil moisture measurements. Using this data set, we first probe the role of factors controlling the spatio-temporal soil moisture dynamics for the different considered soil depth. Special emphasis is thereby given to the role of the vegetation in the space-time relationships of soil Moisture. Secondly, we identify the temporal dynamics of the spatial structure of soil moisture pattern at different soil depth. Thirdly, we investigate the relationship between the mean soil moisture and the spatial variability across time, analysing through the season the optimal sampling strategies to adopt for providing the field areal soil moisture within a given predefined error limit. The result showed that the spatially variable within the held and subsequently through the process of evapotranspiration and the root Water Uptake, plays a non-negligible role in the temporal dynamics of the observed soil Moisture patterns for the superficial layers. The spatial structure of these soil moisture patterns,vas non-existent or only weakly marked. The study finally indicated that a negative correlation exists between the spatial variability and the mean soil moisture, implicitly suggesting that the sampling has to be more intensive for the drier conditions. Besides these results, this study reemphasises the importance of conducting, soil moisture spatial variability studies with measurements performed on the entire hydrological active zone and to adopt temporally unchanged sampling locations in order to progress in the thorough understanding of the physical processes generating the soil moisture spatial variability. (C) 2002 Elsevier Science B.V. All rights reserved.