Monitoring tomato root zone water content variation and partitioning evapotranspiration with a novel horizontally-oriented mobile dielectric sensor

- Novel application of a root zone mobile dielectric sensor in a row cropped greenhouse.
- Dielectric sensor measurements relating temporal-spatial variations in soil water content.
- Partitioning ET using mulched and non-mulched plots for estimating transp. and evap.

We evaluated a recently developed mobile dielectric sensor designed for root zone (0-20 cm) moisture measurements to infer soil and plant water losses associated with evapotranspiration (ET). The sensor was deployed along a tomato row crop grown in a greenhouse (inner area: 240 m2). The mobile sensor generated a horizontally-oriented data array of water content spanning 4 m of the tomato row. The first 2 m section of soil along the row contained eight tomato plants covered by plastic mulch, while the second 2 m section was non-mulched soil. Volumetric soil water content (VWC) was monitored over a 3-month period from August 19 to November 20, 2014. The measurements demonstrated that the VWC declined quickly until reaching the field capacity water content (0.30 cm3 cm−3) both for the mulched and non-mulched sections after each irrigation event. Sensor-based water content monitoring exposed the transition to field capacity, below which ET partitioning was tracked using the water balance equation throughout the experiment. The partitioning of ET into crop transpiration (T) and soil evaporation (E) was evaluated with a modified FAO56 Penman-Monteith (PM) equation, employed as the reference ET (ETo). The coefficients of determination (R2) between the model-estimated and the sensor-measured data were for ET (R2 = 0.849), T (R2 = 0.776) and E (R2 = 0.496). Thus, this mobile sensor can contribute not only to measurement of soil water content in root zone, but also to estimation of plant transpiration and soil evaporation.