Comparison of Multi-Sensor Capacitance and TDR Soil Moisture Methods in Deficit Irrigated Cotton

The objective of this project is to evaluate sensor-based technology to improve land and water resources conservation by refining deficit cotton irrigation management. Multi-sensor capacitance, time domain reflectometry (TDR), and access tubes for neutron probes were installed in LEPA irrigated cotton treatments and monitored through the 2016 growing season. Sensors were installed at the Helms Research Farm, at Halfway, TX, and soil water measurements made at depths of 12”, 24”, and 36” on a daily basis (capacitance and TDR), and periodically with neutron-based moisture measurement. From automatic data collection, a spreadsheet was created taking data from the TDR and capacitance probes at 12”, 24” and 36”, at 12:00 pm daily, starting on June 20th. Data were recorded using the neutron probe periodically during the growing season, with more frequent recordings later in the season. Data were compiled, and plotted using Microsoft Excel. Plots included comparison between neutron probe data and TDR and capacitance data for each day, and month to month comparison of soil moisture estimated by TDR and capacitance methods, including responses to irrigation and rainfall events. These graphs indicated how TDR and capacitance sensors respond to a water event and how the water in the soil profile changed after an event. Initial results indicate that identical pairs of capacitance sensors installed in the same treatment area do not always result in identical readings. This may be due to variation in installation technique, differences in soil characteristics, or differences between the sensors. Both capacitance and TDR sensors respond to rain and irrigation events, but at different rates, sometimes indicating different soil moisture (wetting/drying) trends. The question becomes what trend is correct. Future comparisons of data from these devices to neutron probe and gravimetric data will provide insight into how better to use these tools to manage deficit irrigated cotton.