Evaluation of Saturo infiltrometer for determining field-saturated soil hydraulic conductivity

Pressure infiltrometer (PI) experiments are commonly applied for determination of field-saturated soil hydraulic conductivity, K_s, by the analysis of steady-state infiltration rate from within a single ring. Basically, two approaches can be used for determining K_s: the One-Ponding-Depth (OPD) approach, that uses a single depth of ponding and requires an a priori estimate of the α* parameter, and the Two-Ponding-Depth (TPD) approach, that allows simultaneous estimation of K_s and α*, the ratio between K_s and matric flux potential. Recently, SATURO infiltrometer (METER Group, Inc., USA) was developed as an automated version of the PI method. SATURO automatically calculates K_s by the TPD equations but its functioning presents some specific peculiarities. In particular, the higher pressure head on the soil surface is established before the lower one, and the steady-state infiltration rates required for TPD calculation are sampled after a soaking phase and one or more pressure cycles.

A field test of SATURO infiltrometer was conducted on two sandy-loam soils at Acerra (ACE) and Villabate (VIL) and a clay soil at Monreale (MON). A total of 55 automated SATURO experiments (12 at ACE, 25 at MON and 18 at VIL sites) were conducted and the results compared with those obtained from manual PI tests under comparable conditions in terms of ring diameter and depth of insertion and pressure head values.

Independently of the device (PI or SATURO), the TPD approach yielded K_s values that were not statistically different from those obtained by applying the OPD approach with site-specific α* values of 16, 5.2 and 9.6 m^-1 for ACE, MON and VIL, respectively. When a first approximation literature value of α* = 12 m^-1 was used, K_s calculated by the OPD approach was overestimated on average by 43.9% at MON site but much lower discrepancies were observed at the other two sites, thus confirming that this choice is not expected to introduce large uncertainties in the calculated K_s values.

At ACE, SATURO yielded a mean K_s value numerically similar (D = 4%) and not significantly different from the PI. At MON, the mean of K_s obtained with the PI was larger by 68% than that obtained with SATURO and the differences were statistically significant. At VIL, the mean of K_s obtained with the PI was significantly larger than that obtained with SATURO and the two means differed by 80%. According to the similarity criterion by Elrick and Reynolds (1992), this investigation suggested an acceptable agreement between the two methods given the means of K_s were statistically similar or differed by no more than 1.8 times.

Acknowledgement: This study was carried out within the RETURN Extended Partnership and received funding from the European Union Next-GenerationEU (National Recovery and Resilience Plan – NRRP, Mission 4, Component 2, Investment 1.3 – D.D. 1243 2/8/2022, PE0000005) and the Ministero dell’Università e della Ricerca of Italy, project PRIN 2022 "Smart technologies and remote Sensing methods to support the sustainable agriculture WAter Management of Mediterranean woody Crops (SWAM4Crops)" CUP B53D23018040001.