Management

Getting a glimpse beneath the surface

By Dairy News

A SOIL moisture monitoring project in the southern Riverina is giving dairy farmers real-time information to improve their summer crop management and having big benefits for production.

The project, a collaboration between Murray Dairy and Murray Local Land Services, is exploring the use of soil moisture monitoring tools for irrigation and soil management.

Last year, capacitance probes were installed on two sites, both growing maize, one under pivot and the other under flood. Additional probes will be installed this year after success in the first year of the project.

The probes are installed to a depth of 80 cm and show soil moisture levels at 10 cm increments.

Data collected from the probes show rainfall and irrigation events, changes in water levels in the soil, the movement of water through the profile and the uptake of water by crops.

Probes can be used to understand the amount of water available to plants at any given time and to schedule irrigations to ensure that plants have adequate water at critical stages of their development.

This has assisted farmers to identify issues and make early decisions about how to manage them to avoid yield penalties or damage to crops.

Site one

On the flood-irrigated site, the manager used the probe to make decisions on when to water, considering the price of water and the economic return for each megalitre of water applied.

A soil pit on this site revealed sealing of the soil through consecutive irrigations, impacting on water infiltration and the effectiveness of irrigation.

This was mirrored in probe data, with the water not reaching refill point after the third irrigation.

The refill point is generally the moisture level at which an irrigation is applied, with the aim being to maintain an optimum moisture range at which the plants can achieve maximum yield and quality potential.

Soil structural constraints below 20 cm were identified by examining the soil profile including compaction, lack of organic matter and hard panning.

These constraints typically restrict root development at depth. This correlates with a significant reduction in plant water use observed using the probe as moisture fell below refill point.

With the concentration of production roots within the 0–20 cm profile, once this moisture was depleted, the rate of water use declined.

After identifying these issues, the manager of this site could use the probe data to identify the decline in soil moisture and time irrigations accordingly, preventing water stress which could impact yield potential and dry matter production.

In the longer term, soil remediation options include drying the soil profile to allow cracking and movement of water and organic matter into deeper layers of the soil and use of rotational deep-rooted crops to break the soil open further and add organic matter.

Site two

On the pivot-irrigated site, the manager used soil moisture data to strategically dry and wet the soil to encourage the development of plant roots and better utilisation of soil moisture at depth.

Data from the probe site clearly showed that in late December, when temperatures began to rise, there was an issue with water infiltration into the root zone of the crop, which quickly resulted in poor growth and uniformity.

The farmer used this data to increase application rates and frequencies to lift the moisture level with the maize crop, and then maintain good moisture levels during the prolonged hot and dry conditions.

The manager of this site used the data to allow the profile to dry at strategic periods and encourage better crop utilisation of soil moisture at depth. This encouraged deeper plant roots and the application of correct irrigation to refill the profile. As a result, the farmer could see the real practical benefits of using strategically placed soil moisture probes to monitor soil moisture conditions in conjunction with satellite imagery and visual assessment to view the performance of the crop over the entire pivot.

Public information from probes installed in NSW is available from the Southern Soil Moisture Probe Network at www.soilmoistureprobes.com.au/

Public information from probes installed in Victoria under dryland crops and irrigated and non-irrigated pastures is available from Agriculture Victoria.

Agriculture Victoria has also developed some tech notes on selecting and using soil moisture monitoring technologies for more effective utilisation of water on your farm.

— Murray Dairy