Research papersAssessing the effect of micro-lysimeters on NRWI: Do micro-lysimeters adequately represent the water input of natural soil?

- Microlysimeters (MLs) are commonly used to measure non-rainfall water input (NRWI).
- Detached from the bulk soil, we hypothesized that MLs will exhibit rapid cooling.
- We compared the NRWI on MLs and bulk soil by using the plate-glass method (CPM).
- Significantly higher amounts of NRWI (up to 6-fold) were recorded on the MLs.
- MLs may thus overestimate NRWI and requires calibration.

The use of micro-lysimeters (MLs) by the scientific community for the measurement of non-rainfall water input, NRWI (dew, fog, water vapor) has become more widespread. With MLs being isolated bodies, we hypothesized that changes in heat flux may affect the surface temperatures and subsequently NRWI. Measurements were conducted with MLs of various lengths (3.5, 12, 20, 30, 40, 50 cm for 2014 and 3.5, 12, 50 cm for 2015), and on the adjacent soil that served as a control (COT) using cloths attached to glass plates in Sede Boqer (Negev Desert, Israel) during the late summer and fall of 2014 and 2015. In addition, periodical temperature and moisture measurements were also conducted on additional lysimeters. Non-significant differences in NRWI characterized MLs 12-50 cm-long, which could have been therefore grouped (termed ML12/50). However, these lysimeters and especially the 3.5 cm-long ML (ML3.5) yielded substantially higher values than that of COT, with the ratio of ML12/50 to COT and the ratio of ML3.5 to COT being up to 2.4 and 5.8, respectively, implying, as was indeed found during periodic measurements, lower nocturnal temperatures and subsequently higher moisture content at 0-0.2 cm at the MLs in comparison to COT. This was also reflected in the amount of recorded mornings with effective (>0.03 mm) NRWI: 34 mornings based on the ML12/50 in comparison to only 4 when based on COT. The findings raise serious concerns regarding published data on NRWI and call for proper calibration between the amounts obtained by the MLs and the natural intact soil.