Three-dimensional monitoring of soil water content in a maize field using electrical resistivity tomography

Abstract

Abstract. A good understanding of the soil water content (SWC) distribution at the field scale is essential to improve the management of water, soil and crops. Recent studies proved that electrical resistivity tomography (ERT) opens interesting perspectives in the determination of the SWC distribution in 3 dimensions (3-D). We conducted this study (1) to check and validate the sensitivity of ERT for monitoring SWC distribution in a maize field during the late growing season; and (2) to investigate how maize plants and precipitations affect the dynamics of SWC distribution. We used time domain reflectometry (TDR) measurements to validate ERT-inverted SWC values. We also calculated the evolution of water mass balance to check whether ERT was capable of giving a reliable estimate of soil water stock evolution. We observe that ERT is able to give the same average SWC as TDR (R2 = 0.98). In addition, we showed that ERT give better estimates of the water stock than TDR thanks to its higher spatial resolution. The high resolution of ERT measurements also allows the discrimination of SWC heterogeneities. The SWC distribution shows that alternation of maize rows and inter-rows is the main influencing factor of the SWC distribution. The drying patterns are linked to the root profiles, with drier zones under the maize rows. During small dry periods, the SWC decrease occurs mainly in the two upper soil horizons and in the inter-row area. At the opposite, precipitations increase the SWC mostly under the maize rows and at the upper soil layer. Nevertheless, the total amount of rainfall during the growing season is not sufficient to modify the SWC patterns induced by the maize rows. During the experimental time, the SWC redistribution hardly occurred from maize rows to the inter-rows but lateral redistribution from the inter-row to the maize rows induced by potential gradient generates SWC decrease in the inter-rows area and in the deeper soil horizons.