Salinity Effects on Soil Moisture Measurement Made with a Capacitance Sensor

Three field experiments examined the effects of soil salinity on volumetric soil water content (SWC) measured with a capacitance sensor (CS). They were conducted in field‐grown vegetable crops fertigated with complete nutrient solutions. Experiment 1 compared nutrient solutions with electrical conductivities (EC ns ) of 6.5 dS m −1 (+SAL) and 2.4 dS m −1 (control), applied in equal volumes, following fertigation with EC ns of 2.4 dS m −1 Once +SAL commenced, SWC (0–20‐cm depth) increased rapidly and then remained approximately 30% higher than in the control. Soil matric potential (SMP, 10‐cm depth) was consistently very similar in both treatments. In Exp. 2, increasing EC ns from 2.1 to 5.5 dS m −1 in irrigation treatments receiving 100% of crop evaporation (ET c ) and 25% of ET c caused SWC (0–20 cm) to respectively increase appreciably and maintain relatively constant values. Experiment 3 examined the effect of increased salinity and whether normalizing sensors with higher EC ns alleviated this effect. Treatments were equal volumes of: (i) EC ns of 5 dS m −1 with sensor normalization at EC of 5.2 dS m −1 (SAL‐N5.2); (ii) EC ns of 5 dS m −1 with normalization at EC of 1.9 dS m −1 (SAL‐N1.9); and (iii) EC ns of 1.9 dS m −1 with normalization at 1.9 dS m −1 (control). Previously, the three treatments were fertigated with EC ns of 1.9 dS m −1 The SWC (5–15 cm) increased by approximately 10% in both SAL‐N5.2 and SAL‐N1.9, and maintained relatively constant values in the control. The SMP (10 cm) was consistently very similar in the three treatments. Normalizing the CS at 5.2 or 1.9 dS m −1 had no effect on the response to salinity. In the three experiments, changes in SWC generally paralleled changes in EC of soil water (EC sw ); relative increases were 4 to 7.5% in SWC for each 1 dS m −1 increase in EC sw