Simultaneous and Continuous Measurement of Soil Water Content and Solution Electrical Conductivity in an Irrigated Cornfield Using TDR

Abstract

The transport of soluble salts through unsaturated field soils is directly related to the movement of water, but our understanding of the process is limited because of the lack of experimental data (Kachanoski et al., 1992). Simultaneous and continuous in situ measurement of volumetric soil water content () and soluble salt concentration (c) is essential to clarify the distribution and movement of salts in the soil profile under cropped conditions. Volumetric soil water content and electrical conductivity of bulk soil (EC a) can be measured simultaneously using a time domain reflectometry (TDR) sensor (Dalton et al., 1984; Dirksen, 1999). Furthermore, electrical conductivity of soil solution (EC w), from which soluble salt concentration is estimated with good accuracy (Tanji, 1990), can be calculated from and EC a using a model equation (Wang et al., 2005). Therefore it is possible to measure and c simultaneously and continuously at a point in the field using a TDR probe.

Analyses of Crop Coefficients and Water Balace in an Irrigated Cornfield in the Upper Yellow River Basin

“…These results suggest that approximately 30 of the rainwater and the irrigation water was lost by soil evaporation and about 70 mm of water was supplied to the root zone by capillary rise from the shallow water table. Wang et al (2006) also reported that capillary rise occurred remarkably during the period from the sowing to the first irrigation applied on Jul. 16 and its amount was estimated to be about 80 mm from the water balance of the soil profile in the cornfield.…”

“…4), the four crop growth stages were identified as (1) initial given by the FAO (Allen et al, 1998), which are shown in Fig. 6 and (Wang et al, 2006), as explained later, while the reverse was true in the mid-season and late season stages when crop transpiration occurred actively (Yasutake et al, 2006). These results suggest that Ke was underestimated in the initial and crop development stages because capillary rise is not considered in the dual crop coefficient approach, while ETBo was underestimated in the mid-season and late season stages because the meteorological tower on which various sensors were attached was located in a corner of a 5 5 m plot covered with sparse weeds in the cornfield.…”

An Improvement in the BBH Model for Estimating Evapotranspiration from Cornfields in the Upper Yellow River

“…Following the results obtained by Wang et al (2006), who analyzed the vertical water movement in this cornfield, the parameter c1 was predetermined to be 2 mm day -1 in May (establishment period) when the single layer BBH model was used because the root zone was judged to be confined in the first 40 cm thick layer (Table 3). During the other seasons when the two-layer BBH model was used, c1 and c2 were fixed to be 3 mm day -1 .…”