IMPROVING IRRIGATION PRACTICES in the West Gingin and North Wanneroo areas
By Neil Lantzke
In 2018 the National Landcare Program, through its Smart Farms Small Grants program with the City of Wanneroo, funded Perth NRM to work with a range of irrigators in the North Wanneroo and West Gingin areas to improve water use efficiency. The irrigators involved were: • Eight fruit growers (avocado, mango and citrus) • Four turf farmers • One local government authority (City of Wanneroo) The uniformity of the irrigation system was measured and soil moisture sensors were installed on each of the properties. The project officer worked with the growers to help them use soil moisture and the evapotranspiration (ETo) data to more accurately schedule irrigation.
Fruit growers
Surveys of water use by irrigators on the sandy soils of the Swan Coastal Plain have shown that many can improve their irrigation practices. Soil water monitoring is a tool that can assist fruit growers to decide when to irrigate and how much water to apply. Adoption of soil water monitoring by fruit growers on the sands of the Swan Coastal Plain in Western Australia has not been widespread. The aims of this component of the project were to: • Determine if soil water monitoring is a useful tool that fruit growers will adopt
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• Document the limitations of different soil water monitoring equipment on coarse sands • Define critical soil water levels or ‘refill points’ for different fruit species on coarse sands Capacitance probes and tensiometers were installed adjacent to each other on the eight properties. The equipment was connected to loggers and the growers could view the soil water graphs via the internet. An irrigation agronomist assisted growers with the installation of the sensors and interpretation of the soil water graphs. 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 refill point when using capacitance probes. The capacitance probes were however a more robust piece of equipment that required little or no maintenance. If the soil was allowed to dry out (approximately >40 kPa) this caused air to enter the tensiometers which affected the readings. This required the grower to manually remove the air bubbles from the tensiometer body. The tensiometers functioned well when the soil was kept at the desirable water content.
The Overflow - Autumn 2020
A document titled ‘Using soil water sensors to schedule irrigation of fruit trees on sandy soils’ was written (available to download at https://drive. google.com/uc?export=download&id= 15bOKhH0HrM5O6pFxeQXZiedwjfY NZIyk ). The 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 coarse sands. 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. Most of the growers did not have a documented irrigation plan that was based on long term climatic data and crop factors. 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
