Precision Surface Irrigation Matching Modernised Delivery

April 2012

Introduction

In December 2008 the Department of Primary Industries (DPI) in conjunction with the Northern Victoria Irrigation Renewal Project (NVIRP) started a project to demonstrate the use of Soil Moisture Monitoring (SMM) equipment for scheduling irrigations.

SMM equipment provides a tool to enable irrigators to make more informed decisions about water requirements of various crops, which can result in farm water efficiency gains and increased productivity.

Various types of equipment were installed on farms throughout the GMID. These were mostly border check layouts with two sub surface drip sites and a range of crop types including permanent pasture, annual pasture, winter/summer cropping and lucerne.

The demonstration sites ran for a period of two years and a number of techniques were used to demonstrate what the technology can provide particularly when coupled with a modernised irrigation supply system.

The SMM Demonstration was a collaborative project with NVIRP funded under the Victorian Government’s $205 million Future Farming Strategy and through NVIRP.

Equipment

The majority of equipment used in the demonstration was based around capacitance probes that measure soil water content. Depending on the manufacturer, these have a number of sensors at multiple depths inside a vertical tube which detect where moisture penetrates after irrigation and/or rain, where the plant uses moisture resulting in lower total water content values over time.

During the first irrigation season reference points of water logging, field capacity, refill point and wilting point could be seen and irrigation management lines established on the graphing software. One of the most important components of monitoring soil moisture levels is how to interpret data from an agronomic and information technology perspective.

Once irrigators understood what the data was showing, over time their knowledge and skills improved and irrigation scheduling was further refined. As one participant observed "After the first irrigation, l could see the value in the data being collected. As more data was received during the season, after irrigation and rainfall events, l could analyse the data and schedule irrigations to maximise production."

Full telemetry systems were used in the demonstration and although it is more expensive to purchase than the in-field retrieval system, the data can be viewed anytime and from anywhere internet access is available. The aim of this office based management was to forecast likely irrigation dates based on changes in soil moisture content, taking into account the farmer’s favoured internet weather forecasts and crop growth stage. Using the Goulburn-Murray Water online ordering would allow the required flow rate and volume for that particular date to be secured. The benefits of modernisation began to show as irrigators became more familiar with how to take advantage of the larger and more consistent flow rates, water on demand and online ordering tools.

Picture 1 - Demonstration equipment at Katunga with this site monitoring the differences in soil moisture use of annual versus perennial plants for irrigation scheduling. The solar panels power the system and allow the logging equipment to store information and telemetry to send data.

Benefits

Key points identified by the participant using SMM equipment include:

• Identifying the depth of root-zone activity where the moisture is being used by the plant roots.
• Identifying periods when the plant is not using moisture, therefore not growing at full potential. This can be a result of being too wet (waterlogged) or too dry (moisture stress). When these periods can be identified, management practices can be adopted to minimise these occurrences.
• The opportunity to effectively use rainfall events and information about the depth of irrigation water that enters the soil profile. The target is to apply water to the root-zone and not beyond, the data shows where the roots are using moisture. By knowing the effect of rain on the paddock, irrigation events can be re-scheduled without loss of production.
• Determining when the first irrigation should be planned at the start of the season. The sensors were also able to determine the reduction in the plant water use as autumn approached so the last irrigation for the year could be planned.

Figure 1 - At the start of the irrigation season, the soil water content to 50cm represented by the blue line is close to the full point (blue shaded zone). Farmers have commented on the difficulties in determining moisture accumulation from winter and the water use of plants in spring. The green shaded zone on the graph displays the optimum moisture content for the plant to grow.

Figure 2 - Prediction of the next irrigation event by estimating the moisture content change trend (blue line) on total moisture use (dotted black line).  Recording the impact of rainfall events on soil moisture enables irrigation to be deferred without reducing plant growth.

Most of the irrigators were already quite efficient in the application of irrigation with good delivery and layout to match crop type. One of the border check irrigation sites assessed under the “Irrimate” project developed by the CRC for Irrigation Futures and implemented by RM Consulting Group demonstrated it was operating at around 90% efficiency when drainage was able to be captured in the farm re-use. This is highly efficient indicating very little water applied to the crop is lost from the system. Other than SMM technology, irrigators that have a well laid out irrigation system operating at high efficiency have limited potential to increase their efficiency.

Conclusion

Those landholders with well laid out farms, on a modernised highly responsive delivery system, with constant flow rates and who used the online ordering system were able to be more responsive to the SMM data and as such got more benefit from the equipment.

Some of those participants in the project have bought additional probes to examine different crop water use with similar soil types after the benefits they experienced from the project. This further supports the conclusion the equipment and the subsequent data it produces is useful in improving irrigation scheduling. The most positive growers were those that understood how to exploit the benefits of the modernised delivery system in conjunction with the technology and quality support from service providers.

The full potential of the SMM equipment will only be realised when properties are connected to the modernised irrigation system.

There is continued interest in SMM applications from irrigators outside of the project but no wholesale adoption of the technology as a result of the project to date. Enquiry is expected to continue with the roll out of modernisation across the GMID and uptake of the Commonwealth On Farm Irrigation Efficiency Program.

A factsheet on Soil Moisture Monitoring “Choosing the Right Device” has been produced to help irrigators who might be interested in getting started. www.dpi.vic.gov.au/agriculture/farming-management/soil-water/soil/choosing-soil-moisture-monitoring-device
There is also a final project report with a summary of the equipment used, the key project findings, an evaluation of the technologies and the growers involved.

A copy of the factsheet and report can be obtained by contacting DPI Echuca on (03) 5482 1922 or by return email when contact details provided to Dale.Boyd@dpi.vic.gov.au