What can sensor data tell us about nutrient movement in nurseries?

By David Hunt, Smart Farming Project Officer

Digital sensors can provide an instant overview of how different production systems are performing within a production nursery. In this article, I explain how sensor data is showing us how nutrients move through production systems at the Smart Production Nursery, part of the Smart Farming Partnerships project funded by the National Landcare Program, Greenlife Industry Australia (GIA) and Hort Innovation.

At the Smart Production Nursery in Torbanlea, Queensland, sensors monitor dam and runoff water quality, plant water use, and container leachate, providing a large amount of data. Getting to know the data and watching the daily trends helps the nursery manager to monitor container moisture and estimate when and where nutrients are being used or leached. The data is also proving to be useful in targeting irrigation requirements and adjusting fertigation rates to suit the shallow roots of newly planted seedlings.

Here we look back at a ten-day period of data collected from these sensors during June 2022, and ask the question: “What is the data telling us?”

On 1 June, the weather station forecasts several rain events over the following 10 days. The container moisture content prediction tool using soil moisture sensors (Figure 1), shows there is sufficient moisture in the containers for 1.5 days. A check of the Total Plant Available Water graph (Figure 2) shows that the growing media moisture content is within the green zone of between 25% and 100% moisture.

A check of the individual growing media moisture sensors (Figure 3) confirms that media moisture and electrical conductivity (EC) for the two depths (10cm and 20cm) is at acceptable levels. However, the first predicted rain event did not provide sufficient rain to increase container moisture, therefore a small fertigation was applied on 2 June (A in Figure 3). This is seen as a spike or an increase in moisture and EC content in the two media moisture graphs. At the 10 cm depth, the spike quickly reduces with both moisture and EC content remaining relatively consistent, suggesting the growing media at this level is saturated. The 20 cm deep sensor shows that both moisture and EC content increases slightly, suggesting most of the fertigation is absorbed at this level.

Late on 4 June, a small rain event was sufficient to increase media moisture in the top 10 cm of the container, which is seen on the media moisture graph (B in Figure 3) as an increase in moisture and a decrease in EC. A delay in the reduction of EC between the 10 cm and 20 cm moisture graphs can be seen. This is due to the small volume of rain flushing the nutrients to the bottom of the container increasing EC.

A larger rain event of 25 mm on 6 June is shown on the graph as an increase in media moisture at both depths (C in Figure 3). We know this is a rain event because there is a considerable reduction in EC at 10 cm and a delayed reduction in EC at 20 cm while the moisture content remains high. This indicates that nutrients are being leached from the containers. This is confirmed when we look at the container leachate sensor that captures and monitors the leachate as it leaves the container (Figure 4). We see there is a corresponding increase in container leachate pH and EC on 6 June.

Following the leachate runoff through to the runoff collection drain sensor (Figure 5), we initially see a reduction in the EC due to nutrients being diluted from the rain. Then, there is an increase as the nutrients being leached from the containers and growing beds start to reach the runoff collection drain.

Monitoring the container moisture and EC content is allowing the nursery manager to maintain optimum growing conditions across the nursery. However, the nursery manager is now applying this process to the different growth stages of the plants. When a new crop is put down, the moisture and EC sensor in the top 10 cm of the container is used to determine irrigation for the new seedlings. As the seedlings’ roots grow, both the 10 cm and 20 cm moisture and EC sensors are used to adjust fertigation events, ensuring moisture and nutrients are not a limiting factor.

When this data is used in combination with the weather data and the container moisture prediction tool, the nursery manager can manage irrigations to suit the predicted weather conditions of the next few days rather than what had happened yesterday.

Using all sensor data and looking at the trends across the whole system is providing not only a snapshot of when and where nutrients are moving through the nursery, the data is helping to restrict the loss of nutrients from the containers, reduce fertiliser costs and ensure nutrient runoff is within the environmental requirements.

The Smart Farming project has been funded by Hort Innovation nursery products research and development levy and the Australian Government’s National Landcare program. Hort Innovation is the grower owned, not-for-profit research and development corporation for Australian horticulture.