THE CLIMATE KELPIE BLOG: Soil moisture monitors lift the veil on the root zone

Posted by BCG on 28th June 2019

While farmers are often adept judges of crop and pasture yield potential, soil moisture monitoring technology now provides concrete data on plant available moisture to help drive decision making.

Image 1: Soil moisture monitoring probes have been established at dryland cropping and pasture locations throughout Victoria. Source: Dale Boyd.

Real time data from Agriculture Victoria’s soil moisture monitoring probes is available online for 17 cropping and 18 pasture sites around the state. Farmers can use the interactive website to track soil moisture throughout the year, evaluate the effectiveness of rainfall events and help them with decisions such as sowing programs and in-crop fertiliser application.

Already proven in irrigated situations, the probes were first installed in dryland cropping sites as part of a pilot program to test their value in identifying important management triggers. The probes were established in conjunction with local cropping groups to inform discussions about soil moisture reserves and seasonal risk.

Cropping sites

The pilot program clearly demonstrated the value in better understanding the subsoil situation. By comparing data with land management activities, growers were able to confirm their estimates of crop potential, and in turn make better decisions.

For instance, the monitoring site near Brim in North Western Victoria suffered from a lack of moisture throughout the 2018 season and data from the probes showed that there was not enough soil moisture to finish a grain crop. This information convinced the grower that cutting for hay was the most informed decision, allowing him to conserve the little soil moisture that remained.

Figure 1. The dryland cropping site at Brim suffered from poor soil moisture throughout 2018, but after a storm delivered more than 100 millimetres of rainfall in December 2018 the soil moisture probes showed excellent recharge throughout the profile. Summed soil moisture is shown by the line, and rainfall by the bars. Source: Dale Boyd.

Following a solid 100-millimetre plus rainfall event during a December storm, soil moisture data from the probes showed excellent recharge of the system with the moisture infiltrating a full metre to fill the profile.

The cropping probes provide soil moisture and temperature at 10 centimetre intervals from 30cm to 100cm depth, as well as rainfall at the site, providing growers with a good understanding of total soil moisture and where it is in the profile.

“Experience with grower groups has shown that these probes enable more informed decision making,” says Agriculture Victoria agronomist Dale Boyd. “They give growers a better understanding of how much moisture the soil can hold and are being used to guide crop selection. We’ve even seen growers use the data to decide whether to sow a longer or shorter season variety.”

“The probes have proven invaluable for the farmers hosting them. But the information is also of interest to others to get a sense of how the season is progressing,” he says.

“Growers can also access our interpretation of the data through the Agriculture Victoria Soil Moisture Monitoring newsletter that we email to subscribers throughout the growing season (Figure 2). It helps them to better understand seasonal conditions and is another tool to inform their own decision making.”

Figure 2. The Soil Moisture Monitoring newsletters compile ‘speedo’ diagrams to compare soil moisture in the profile at each site. For instance, in January 2019 the soil moisture at the Brim dryland cropping site is close to field capacity, whereas at the same time in 2018 the profile was around 50 per cent of field capacity. Source: Dale Boyd.

Moving on to fresh pastures

Now the system is being deployed in pasture paddocks to serve the dairy and meat and wool industries.

Again, working with farmer groups the Agriculture Victoria team aim to get a better understanding of the sort of soil moisture triggers that could be used to better manage pasture growth and availability throughout the season.

“The pasture sites are in the higher rainfall areas where it is temperature, rather than soil moisture, that is likely to be the limiting factor for pasture growth throughout the winter,” says Mr Boyd. “For this reason, we have installed the temperature and moisture sensors starting at 10cm to help understand the impact that soil temperature has on growth potential.”

Image 2: The soil moisture monitoring network has recently expanded to include pasture sites. Source: Dale Boyd.

Already the probes have revealed some surprising information about the potential of different pasture species to access soil moisture at depth. Perennial ryegrass has always been considered shallow rooted, but early data from the soil probes has shown perennial ryegrass pastures able to extract soil moisture from as deep as 60 to 80 cm at some sites.

“It is good to see that perennial ryegrass can use moisture from deeper in the profile to survive dry periods, but the all-important dry matter production is still more dependent on utilising shallow soil moisture. We look forward to learning more about our pasture sites in the coming seasons,” says Mr Boyd.

“We hope to use the probes to better understand how seasonal conditions can impact on pasture growth and what information will help inform better decision making around stocking rates and feed budgets. We will be looking to identify the triggers that drive season length and the potential to adjust inputs such as nitrogen or plant growth hormones.”

Access to the soil moisture monitoring site data and industry-specific email newsletter is available on the Agriculture Victoria soil moisture monitoring pages for dryland cropping areas and pasture areas.

Contact

Dale Boyd, 03 5482 0439, dale.boyd@ecodev.vic.gov.au

Agriculture Victoria soil moisture monitoring for dryland cropping areas. Use ‘dpi’ as the username and password.

Agriculture Victoria soil moisture monitoring for pasture areas. Use ‘agvic’ as the username and password.