Calibration of Granular Matrix Sensors for Irrigation Management

Granular matrix sensors (GMS) represent an alternative technology for measuring soil water to schedule irrigation. When GMS were tested by drying them to measure changes in electrical resistance with decreasing water content, their resistance response to drying in air in an oven was similar (t = −0.87, 134 df) to that for drying in a field soil, with a response curve that suggested GMS could be used to measure soil water potential (Ψ). Granular matrix sensor meter readings were compared with tensiometer, neutron probe, and gravimetric measurements of soil water in the root zone of potato (Solanum tuberosum L. cv. Russet Burbank) grown in silt loam. Measurements with GMS were closely related to soil water potential measurements and to soil water measured gravimetrically or by neutron probe. Meter model 30KTC, as supplied by the manufacturer, when calibrated against tensiometers, had a linear response represented by the equation y = −6.44 − 0.738 x, where y = Ψ J kg−1), and x = 30KTC meter reading (dimensionless units) of GMS, with r2 = 0.89. Granular matrix sensors were used to monitor transitory soil water stress treatments in an experiment to determine potato response to water stress.