How healthy is your irrigation water source?

By David Hunt, GIA Smart Farming Project Officer
 

Over the past decades, considerable industry research has developed irrigation water quality guidelines to promote the benefits of healthy irrigation water in nursery production. This research has shown that high quality clean irrigation water not only improves crop growth, uniformity, and marketability but helps to reduce plant throw-outs, the amount of chemical or fertiliser needed, and the amount of energy required to transfer and disinfest the irrigation water (Rolfe et. al., 2000).

So how do you know your irrigation water is of good quality and ‘clean’?

Unfortunately, irrigation water quality cannot be determined by its visual appearance alone. Just because irrigation water ‘looks clean’, it does not necessarily mean it is healthy. The only way to answer this question accurately is to have a full lab test done to identify the biological, chemical and particulate elements dissolved in the water. However, collecting irrigation water samples can be time consuming and costly considering most labs require the irrigation water samples to be delivered on the same day of collection or frozen for transport.
 

Nonetheless, a full irrigation water analysis is beneficial as it will not only provide a water quality baseline, but it will also help to identify the type and level of filtration or disinfestation needed for the irrigation water source. An irrigation water analysis should also be done when any major changes are made to the water application or collection infrastructure as this can change the irrigation water quality especially when runoff water recycling is implemented. This is more important if fertigation is used as the existing elements and nutrients in the source irrigation water will change the water chemistry when fertiliser is added.

An alternative to regular lab tests would be to either install remote irrigation water quality sensors at various strategic locations around the production nursery, or to implement a regular manual sampling regime where the irrigation water is tested on site using a desktop testing unit such as a photometer. Monitoring your source irrigation water quality will provide an early warning of potential changes in water chemistry and the current nutrient load already dissolved in the water. This will provide quick feedback to the production nursery manager so that management decisions can be made quickly before any potential damage is done.

As part of the Smart Farming Partnerships project funded under the National Landcare program, Greenlife Industry Australia (GIA) and Hort Innovation, a number of remote irrigation water sensors have been installed at key locations around the projects’ Smart production nursery. These sensors feed data back to the operations’ dashboard (Hitachi control tower) where the production nursery manager can see the water quality parameters of the dam and main collection drain in real-time. A free chlorine sensor is also being installed in the main storage tank to monitor residual chlorine after disinfestation. Growing media moisture and leachate sensors are also installed to monitor container moisture and the volume of leachate released. These will provide constant feedback of both irrigation source and runoff water quality across the production nursery and acts as an alert system for any changes to the irrigation water chemistry. These systems also allow the production nursery manager to ensure any water released to the local waterways meets environmental water quality standards.  
 

A combination of sensors, or sonde, for Nitrate, Phosphate, total Alkalinity, Sulphate and Iron were considered. However, for various reasons including reliability and cost, a desktop photometer was chosen as a more economical alternative. A desktop photometer allows production nursery staff to take irrigation water samples from any location and test levels of a wider variety of parameters with relatively little cost. The irrigation water quality data generated by the photometer is automatically transferred to the dashboard to assist in decision making, such as the daily fertigation recipe.

Another major concern is the nitrate levels in the dam during drier weather or during drought. Low water levels mean nitrates and nutrients from irrigation leachate flowing back to the dam will increase considerably without fresh water. This can cause algal blooms, or in extreme situations, a dam inversion that changes the chemical and physical properties of the stored water making it unsuitable for irrigation. Trying to correct a dam inversion requires time and major inputs of chemicals and fresh water, which is costly, but what is worse is if there is no alternative water supply, irrigating with this water could lead to complete crop losses. Monitoring the temperature and nutrient levels in the dam will help to identify the point when an alternative water supply should be used.

By using a combination of remote irrigation water quality sensors and the photometer, the Smart production nursery management can manipulate the fertigation program accordingly, ensuring the crop nutrient budget is met without causing excessive nutrient leaching. Monitoring irrigation water quality has the potential to deliver other benefits such as providing good quality clean water for irrigation, reducing fertiliser usage, conserving water, and increasing both crop performance and environmental considerations.
 

(References)

Rolfe, C., Yiasumi, W., & Keskula, E., 2000. Managing water in plant nurseries. 2^nd Ed. ISBN: 0734711808. NSW Agriculture. (3^rd Edition available)

Further reading

GIA: Nursery Papers, November 2020. Water management for production nurseries.

GIA: Nursery Paper, May 2014 Issue no.4. The Importance of Suitable Sources of Irrigation Water to Nursery Businesses.

Nursery levy at work: Water Disinfestation. A Comparison of Proven Water Disinfestation Systems for Production Nurseries.

Irrigation toolbox Calculators: https://nurseryproductionfms.com.au/irrigation-toolbox-calculators/