First of all, if we are talking about an annual crop it is appropriate to install it during the first stages of the crop development in order to preserve the root system of our reference plant. For crops such as tomato, maize or strawberry, we will hence prefer the first weeks of growth.
Another crucial aspect is the representativeness of the soil where we install our moisture probe: the contact between the soil and the probe, the absence of preferential paths and a homogenous structure compared to the rest of the field are key aspects in order to collect representative data. For perennial crops, installing before winter (under our climate) offers the double advantage of homogenizing the structure thanks to the winter rains and allows a right determination of the field capacity, that will be further a reference point for our irrigation scheduling.
Finally, there is a third fundamental aspect to take into account for drip irrigated crop: the size of the wet bulb. It is essential to determine the size of the wet volume required for an optimum crop growth, and to place the capacitive probe accordingly. Moisture probe located at the periphery of the bulb will often be more meaningful than a probe right near to the emitter. In this sense, installing the probe during the irrigation peak demand (for instance in August/September for citrus under our climate) is suitable. If the probe can’t be installed at that moment, an observation of the profile can be realized to know the dimensions of the root zone and the volume of the wet bulb. This information can be used later to determine the probe location.