Soil water monitoring is a tool that can assist fruit growers to decide when to irrigate and how much water to apply.
In 2018 the National Landcare Program and the City of Wanneroo funded work to assist fruit growers in the West Gingin and North Wanneroo areas adopt soil water monitoring to improve their irrigation
practices. Soil water sensors were installed on eight properties (four avocado, two citrus and two mango farms). All of the farms were located on sandy soils.
The tensiometers and the capacitance probes were connected to loggers and the growers could view the data via the internet. An irrigati on agronomist assisted the growers with the installation of the sensors and interpretation of the soil water graphs.
The coarse sandy soils of the Swan Coastal Plain have a very low water holding capacity and the irrigation management is quite different to that on sandy soils that are used elsewhere for horticulture. This document contains guidelines for the installation of soil moisture sensors on sands, information on how to interpret the results and discussion on the benefits and limitations of different soil water monitoring equipment. Guidelines for soil water monitoring and critical soil tensions at which irrigation should be applied are presented for citrus, mangoes and avocados when grown on these sands. Tensiometers and capacitance probes were
installed at the same site on each property to allow comparison of the two types of equipment. It was found that tensiometers are better suited than capacitance probes in determining refill points in the coarse sands. Tensiometer readings plummet as the soil dries which makes it easier to determine the refill point while soil moisture decreases slowly as the soil dries out making it more difficult to determine the refi ll point.
The study showed that in some cases growers were applying excessive amounts of water while in other cases growers were under irrigating. Prior to using soil water sensors most growers were not adequately adjusting their irrigation to account for days with significantly higher or lower evapotranspiration (ETo).
Most of the growers did not have a documented irrigation plan that was based on long term climatic data and crop coefficients.
Over the first six months of the project the growers gained a better understanding of how to interpret trends in the data and the benefits and limitations of soil water sensing. The majority of the growers involved in the study now view the soil water data regularly and use the information to help schedule their irrigation. The overall response to the study has been positive and some of the growers have bought additional soil water sensors and installed them in other irrigation blocks.