To know when irrigation is required, it is important to have an accurate record of soil moisture. A simple method of doing this is to dry a sample of soil and calculate the water content. More modern methods include time domain reflectometry (TDR), where two probes are inserted into the soil and the meter calculates the time taken for a pulse to travel between the probes. From this, the moisture content of the soil can be calculated. It is much faster and more readings can be taken than by the old method. Here AgResearch technical officer Ross Gray holds a portable TDR probe.