For efficient irrigation, the farmer or orchardist needs to measure or estimate the soil moisture. This can be done by drying a sample of soil and calculating the moisture level, or by calculating evapotranspiration (the loss of water through evaporation and plant transpiration). An alternative is a time domain reflectometry (TDR) meter, which, when pushed into the soil, calculates the time taken for a signal to go between the two probes. This is directly related to the soil moisture content. Ross Gray from AgResearch is holding a TDR probe.
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Photograph by Ross Gray
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