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n Drain Gauge User's Manual 4. Collecting Data where mV is the output from the water depth sensor in the siphon chamber. This generic calibration function should be accurate enough for nearly all applications. If extreme accuracy is desired in inter -flush solution volume measurement, then you must perform a custom calibra- tion by incrementally injecting known volumes of local soil solution into the calibration port (clear tube) and recording sensor mV output after each solution injection. Note that care should be taken when performing a custom calibration to flush the entire injected solution volume from the calibration tube into the calibration chamber with air before recording the mV output from the water level sensor. Root Incursion If the Drain Gauge is installed at too shallow a depth, it is possible for plant roots to grow into the wick and either use water from, or potentially clog the drain gauge. To prevent this, each new drain gauge is shipped with a root inhibiting fabric (Bio-barrierTM, Reemay, Inc.) placed below the wick fabric on the wick plate. This fabric is impregnated with Treflan® (Trifluralin) root inhibitor. The root inhibitor is slowly released into the soil sur- rounding the fabric, and builds up a layer of — 10cm thick- ness where roots will not penetrate. The effective lifetime of the Bio -barrier is several decades, so the fabric should not have to be replaced over the life of the drain gauge. Treflan is a mitosis inhibitor, which prevents plant roots from growing via cell splitting. It is possible (although unlikely) that the roots of woody species that grow via elongation may be able to penetrate the inhibitor layer and grow into the wick. If this is a concern, it may be neces- sary to place additional Bio -barrier in the divergence con - 26 n