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Salinity Effects on Soil Moisture Measurement Made with a Capacitance Sensor

^a Dpto. Producción Vegetal, Univ. de Almería, La Cañada, 04120 Almería, Spain
^b Research Station of the Cajamar Foundation, Autovía del Mediterráneo, km. 416.7, 04710 El Ejido, Almería, Spain
^c Dpto. Ciencias del Agua y Medio Ambiente, Instituto Tecnológico de Sonora, 5 de Febrero 818 Sur, Cd. Obregón, Sonora, México

View larger version (8K): [in this window] [in a new window]   Fig. 1. Schematic representation of nutrient solutions applied to the control and the standard nutrient solution with added salts (+SAL) treatments throughout Exp. 1. The electrical conductivity of the nutrient solutions applied (ECns) and the volumes applied, expressed as a percentage of crop evapotranspiration (ETc), are shown.

View larger version (16K): [in this window] [in a new window]   Fig. 2. Schematic representation of the application of nutrient solutions and water to plots of the well- and deficit-irrigated treatments throughout Exp. 2. The electrical conductivity of the nutrient solutions applied (ECns) and of the water applied (ECw), and the volumes applied expressed as a percentage of crop evapotranspiration (ETc) are shown.

View larger version (17K): [in this window] [in a new window]   Fig. 3. Schematic representation of the application of nutrient solutions and water to plots of the SAL-N5.2, SAL-N1.9, and control treatments throughout Exp. 3. The electrical conductivity of the nutrient solutions (ECns) and water applied (ECw) are shown inside squares associated with unbroken arrows. The volumes applied, expressed as a percentage of crop evapotranspiration (ETc), are shown inside rectangles associated with broken arrows. During the salinity treatment periods, the SAL-N5.2 and SAL-N1.9 treatments received ECns of 5 dS m–1, and the control treatment received ECns of 2 dS m–1. Capacitance sensors used in the SAL-N5.2 and SAL-N1.9 treatments were normalized at 5.2 and 1.9 dS m–1, respectively. Immediately following salinity treatment periods, water-only irrigations were applied to leach salts.

View larger version (18K): [in this window] [in a new window]   Fig. 4. For Exp. 1: (a) electrical conductivity of the soil solution (ECsw) at 10-cm depth, and (b) volumetric soil water content (SWC) measured with the capacitance sensor (CS) at 0- to 20-cm depth for the control treatment, irrigated continuously with a 2.4 dS m–1 nutrient solution, and for the +SAL treatment in which the electrical conductivity of the nutrient solution (ECns) was increased from 2.4 to 6.5 dS m–1 after 22 Mar. 2004. Data are the means of four replicate measurements. Error bars in (a) represent the standard error of the mean, and in (b) represent the average pooled standard error of the mean of the two treatments. On 11, 18, and 25 March, ECsw was identical in the control and +SAL treatments. The vertical arrows indicate when the 6.5 dS m–1 nutrient solution was first applied to the +SAL treatment.

View larger version (15K): [in this window] [in a new window]   Fig. 5. Experiment 1: (a) soil matric potential (SMP) at 10-cm depth, and (b) volumetric soil water content (SWC) measured with the capacitance sensor at 0- to 20-cm depth, measured at 0600 h, of the standard nutrient solution with added salts (+SAL) treatment plotted against the equivalent data from the control treatment for the period 3 Apr. to 24 June 2004. The unbroken lines are the fitted linear regressions, and the broken lines represent the 1:1 line. Data are the means of four replicate measurements.

View larger version (25K): [in this window] [in a new window]   Fig. 6. Experiment 2. For well-irrigated treatments, electrical conductivity of the soil solution (ECsw) at 10-cm depth during (a) 5 Apr. to 8 May 2004, and (b) 8 to 22 May 2004. For well-irrigated and deficit-irrigated treatments, soil matric potential (SMP) at 10-cm depth during (c) 5 Apr. to 8 May 2004, and (d) 8 to 22 May 2004; volumetric soil water content (SWC) measured with the capacitance sensor at 0- to 20-cm depth for (e) 5 Apr. to 8 May 2004, and (f) 8 to 22 May 2004. The electrical conductivity (EC) of the applied nutrient solution or water was 2.1 dS m–1 before 10 April, 5.5 dS m–1 for 10 April to 1 May, 0.4 dS m–1 for 2 to 7 May, and 2.4 dS m–1 after 8 May. Data are the means of four replicate measurements. The error bars in each panel represent the averaged pooled standard error of the mean for the two treatments. In (c), (d), (e), and (f), the upward arrows represent the periods in which the deficit-irrigated treatments were applied. In (a), (c), and (e), the downward arrows represent the period in which a series of salt-leaching applications of water only (EC of 0.4 dS m–1) were applied.

View larger version (27K): [in this window] [in a new window]   Fig. 7. Experiment 3. For the control (electrical conductivity of the nutrient solution [ECns] of 1.9 dS m–1), SAL-N1.9 (ECns of 5 dS m–1, normalized at 1.9 dS m–1), and SAL-N5.2 (ECns of 5 dS m–1, normalized at 5.2 dS m–1) treatments: electrical conductivity of the soil solution (ECsw) at 10-cm depth during (a) 24 Dec. 2005 to 11 Apr. 2006, and (b) 12 Apr. to 30 June 2006; volumetric soil water content (SWC) data measured with the capacitance sensor, for 5- to 15-cm depth, during (c) 24 Dec. 2005 to 11 Apr. 2006, and (d) 12 Apr. to 30 June 2006; soil matric potential (SMP) at 10 cm depth during (e) 24 Dec. 2005 to 11 Apr. 2006, and (f) 12 Apr. to 30 June 2006. The SWC data were measured at 0600 h each day; SMP was measured at 0900 h. The period 24 Dec. 2005 to 11 Apr. 2006 included the first salinity treatment period, and the period 12 Apr. to 30 June 2006 included the second salinity treatment period. Data are means of three replicate measurements. The error bars in each panel represent the average pooled standard error of the mean for the three treatments. The upward arrows represent the periods in which the higher salinity treatments were applied, and the downward arrows represent the periods in which a series of salt-leaching applications of water only (EC of 0.4 dSm–1) were applied.

View larger version (14K): [in this window] [in a new window]   Fig. 8. Experiment 3: volumetric soil water content (SWC) measured with the capacitance sensor at 0600 h for treatments of 5 dS m–1 nutrient solution in which capacitance sensors were normalized in solutions of 5.2 dS m–1 (SAL-N5.2) vs. 1.9 dS m–1 (SAL-N1.9) for the period 24 Dec. 2005 to 11 Apr. 2006, for (a) the 5- to 15-cm depth, and (b) the 15- to 25-cm depth. Data are the means of three replicate measurements.

View larger version (10K): [in this window] [in a new window]   Fig. 9. Experiment 3: the difference in volumetric soil water content (SWC) measurements between the SWC measurements made in 5 dS m–1 nutrient solution with capacitance sensors normalized in a solution of either 1.9 dS m–1 (SAL-N1.9) or 5.2 dS m–1 (SAL-N5.2) and the control treatments plotted against the corresponding difference in electrical conductivity of the soil solution (ECsw). The SWC data are for both the 5- to 15- and 15- to 25-cm soil depths, and the corresponding ECsw data are for the 10- and 20-cm soil depths. The SWC data were measured at 0600 h for the days on which ECsw data were collected. Data are from the period 29 Dec. 2005 to 29 June 2006, and are the means of three replicates.