How water quality sensors are helping with production nursery decisions

By David Hunt, GIA Smart Farming Project Officer
 

As part of the Greenlife Industry Australia (GIA) delivered Smart Farming Partnerships project funded under the National Landcare program and Hort Innovation, a combination of water quality sensors and a desktop photometer are highlighting how water quality fluctuates, and how quickly nutrients are leached from the containers. This information is helping the Smart Farming nursery manager to refine daily irrigation requirements and production processes resulting in healthier plant development and a cleaner local waterway.

Production nurseries that are NIASA and EcoHort accredited know that water quality monitoring is a reportable parameter under those programs. Good water quality helps to reduce any negative environmental impact if runoff water is released to the local waterways during a rain event. So, automating water quality monitoring has many benefits.

In containerised production nurseries, water quality influences not only plant health but can also determine the amount of resources used during production. The amount of dissolved organic and inorganic particles in the water will determine the level of filtration and disinfestation required. This in turn influences water treatment times, pump runtimes and energy use needed to process the water before irrigation can occur.

At the Smart Farming production nursery, a combination of permanent in-situ sensors and a desktop photometer is helping the nursery manager to monitor water quality and make production decisions. Although interpreting and integrating the data into daily management decisions is ongoing, preliminary results are highlighting how water quality fluctuates, how quickly nutrients are leached from the containers, and how much water is held within the containers.
 

Every day the nursery manager checks the dam pH and electrical conductivity (EC) data to ensure the source water is within acceptable limits. The irrigation runoff water is also checked to see if there has been any excessive leaching of nutrients. The weather station is checked to see if there has been a major rain event overnight that may have caused any changes in water quality. If the pH or EC has changed considerably it raises the questions - why, what has happened to cause a change? Is there a potential for this change to impact today’s irrigation requirements?

The basic water properties of pH indicate how acidic or alkaline (or neutral) the water is. EC indicates the combination of the naturally occurring salts as well as added fertiliser components dissolved in the water. These are monitored because pH and EC will influence whether the water needs to be adjusted before use, or if a proportion of town water should be used to suit the fertigation solution. This is especially important if irrigation runoff is captured and reused, or if there is a potential for other contaminants and nutrients to be washed onto the property from upstream or the surrounding area.
 

If there are any concerns about water quality, water samples are taken for further testing with the desktop photometer and the results used to determine what course of action is needed, e.g., change the water source to town water, or adjust the fertigation solution. One unforeseen benefit of this process is that now, before town water is to be used, a quick test is done to identify the pH, EC, and alkalinity or the concentration of carbonates and bicarbonates dissolved in the town water that can affect the plants uptake of calcium and magnesium. These tests have shown that the town water alkalinity regularly fluctuates and at times requires the fertiliser solution to be adjusted to maintain an appropriate calcium to magnesium ratio for plant uptake and to reduce scale build up in the irrigation system.

Water samples are also taken to monitor the nitrate and phosphate levels at certain points to help identify how much is applied to the containers and how much is leached from the containers. Water tests at the storage tank after disinfestation provides the starting point for the fertiliser formula. Water tests of samples taken at the sprinklers confirm how much is applied, while tests of the runoff water after an irrigation event indicates how much is being flushed from the growing areas.
 

In one testing round it was identified that 30 ppm of the nitrate was being emitted at the sprinklers, but 20 ppm was recorded in the runoff water being returned to the dam. This has led to the ongoing monitoring of the irrigation water quality and adjustments to the fertigation formula or the irrigation duration to reduce leaching and ensure the fertiliser remains in the containers longer for plant uptake. How these adjustments are affecting fertiliser usage or plant development is still being assessed by the nursery manager.

Another example of the benefits of water quality monitoring was highlighted during the recent flooding rains. The heavy downpour and large volume of water running onto the nursery from the surrounding area caused the dam to overflow. However, by tracking the water quality, the nursery manager knows that the levels of nitrates and phosphates in the discharged water was within acceptable limits and would not have any impact on the local waterway.

Over the next 12 months, it is expected that through ongoing water quality monitoring and in combination with the other plant monitoring sensors onsite, production systems and practices will be refined further. It is anticipated that this information will provide a better understanding of how water quality is influencing resource use and will allow resource use and costs to be quantified for each production cycle.

Further reading

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

Hort Innovation funded project ‘Digital remote monitoring to improve horticulture’s environmental performance’ (ST19024) using the Hort Innovation nursery products research and development levy and the Australian Government’s National Landcare Program.