Case Study – Wheat


  • Probe: 80cm
  • Crop: Wheat
  • Soil Type: Deep sand soil
  • Site: North East of Perth.
  • Situation: Dryland

An 80cm probe was installed into a wheat crop in 2012. The soil was mainly sand throughout with increasing clay content below 70cm. The wheat was planted early June and the probe was installed late June. The Hornet unit monitored soil moisture at 8 depths from July through to December 2012.

wheat case study

    • The upper profile of this sandy soil reaches field capacity at about 14-16mm (or 14-16% moisture) and reaches stress point at about 6-8mm (6-8% moisture). Levels above field capacity leach radidly and levels below the stress point are tightly held by the soil and less avalaible to the crop.
    • The blue line is a good indicator of effective rainfall throughout the season. For example on the 4th and 5th of September the soil moisture levels incresed from 6 to 30mm. Over the same two days there was about 23mm of rain. This pattern is repeatable with rainfall events throughout the season.
    • Depending on the amount of rain, most moisture is held within the top 40cm of the soil profile. It is only when moisture in the top 10-40cm drops towards the stress point that the crop starts to access water below this level. The amount the crop is using from these lower levels was very low and only occurred when moisture in the top layers was depleted (late September – early October 2012).

Growing Period

    • There was a very sandy layer around 50-60cm with low water holding capacity. Very little water was used from this layer.
    • Heavy rain events during the growing period result in rapid movement of water down the soil profile. These events can lead to nutrient leaching in these light soils.
    • The crop went into server stress from early October onwards. Crop yields were down 30% or more.




  • In sandy soils the key is to try and hold moisture in the top 40cm. This could be achieved through increasing the water holding capacity of the soil with added organic matter or polyacrylamides.
  • Sow the earliest possible with short season varieties in order to reduce the impact of highly variable Spring rains. Use the Hornet to assist in determining the optimum sowing time.
  • Use the Hornet to determine the timing of in crop nitrogen applications. Best to time nitrogen applications when there is sufficient moisture in the top 30cm.
  • Chemical and physical layers often exist in the soil and can inhibit or enhance root growth. The hornet can assist in identifying these layers and initiate the need for further investigation.
  • The measurement of EC at each sensors can also assist in the presence of salts in the soil and in some cases fertiliser.