An open-source automation unit for measuring infiltration flux and (un)saturated soil hydraulic conductivities using tension infiltrometry

Abstract:

Surface infiltration capacity, as well as saturated and unsaturated soil hydraulic conductivities (K_sat, K(h)) often exhibit high spatial variability and their measurement typically requires a large sample size while the time to reach steady-state conditions may be considerable. Methods involving ponding tend to overestimate K_sat since they include preferential flow through macropores that become activated only during highly intensive rainfall. Tension infiltrometry is able to distinguish between preferential flow and matrix flow but measurements are cumbersome. To facilitate measurement of K_sat and K(h) in the field, we developed an open-source based automation prototype unit that measures water height in the feeder reservoir of a tension infiltrometer at 1.0 mm resolution and at user-programmable time intervals. The system employs differential pressure sensors and an Arduino UNO board with data-logging capabilities for overall unit control. Up to four tension infiltrometers can be used simultaneously by the system. The unit was tested extensively on soil horizons having highly different characteristics in volcanic sub-humid central Mexico. Infiltration fluxes as well as K_sat and K(h) values obtained in this way did not differ statistically from those measured manually. We conclude that effective soil hydrological data recording can be achieved using the automated unit presented here, at a very affordable price and with minimal supervision, implying a major reduction in invested time compared to manual measurement while avoiding the errors potentially associated with manual data capture. Specifications for unit construction and programming are available from the senior author upon request.