AgMemo Central Agricultural Region

Stored soil water is important in 2017

Two female DAFWA staff with a electronic rain gauge
Development Officers Stacey Hansch and Bec Swift with a newly installed rain gauge at Wickepin

Stored soil water is likely to make a significant contribution to crop yield this year due to the high January and February rainfall and the low May and June rainfall.

Department of Agriculture and Food, Western Australia (DAFWA) Development Officers are using the Soil Water App (SWApp) to assess the impact of stored water on this year's crop performance.

These officers are a part of the "Building capacity for crop protection and agronomy in the Western Region" (Regional Research Agronomy) project that is jointly funded by DAFWA and Grains Research and Development Corporation (GRDC).   

The SWApp, developed by the University of Southern Queensland and GRDC, is a new, simple, soil water app designed to help farmers and consultants track plant available water in their paddocks. 

The app is user friendly and capable of providing farmers and advisers with an estimate of plant available water in their soil during fallow and early crop phase.

It is available free from the App Store and is suited to iPhone and iPads at this stage.

The app uses the modelling routines used in complex daily water balance models such as Howleaky and ApSim.

How it works

Once the app is downloaded on to your iPhone or iPad, the user simply defines some inputs from drop down screens. These include:

  • Creating a new site by providing property name and paddock name
  • Selecting the closest Bureau of Meteorology weather station (e.g. Northam)
  • Select a soil type from a list with varying plant available water capacity (PAWC). Soils with a higher PAWC will provide greater capacity to store water and will give high grain yields (e.g. sand over light clay with PAWC of 100mm).
  • Select the starting period or when the previous crop was harvested and the ending period or when the current crop will be harvested (1 November 2016 and 2017)
  • Select the starting PAWC (e.g. 0%, because the previous crop has most likely used all of the soil water).
  • Select the fallow/crop type (e.g. wheat sown 27 May 2017 with maturity date of 25 September).
  • Select stubble cover during fallow and crop, if unsure select 60%.
  • Save the settings, the app will access weather data and predict your soil water.

Using the example shown in Figure 1, we can see the January - February rains increase the soil water content to field capacity.

Since February there has been little follow-up rain, but because the soil had no weeds, there is still significant stored soil water.

Currently, at Northam the soil is at 82% of capacity (PAWC), equivalent to of 82mm (Figure 1).

The water balance from 04/11/2016 to 22/06/2017:

Rainfall 318mm
Evaporation 105mm
Transpiration 13mm
Runoff/drainage 35/83mm (from the heavy falls in the summer)

The user can tap on a water balance table to see estimates of future water balance (22/06/2017-28/12/2017) components.

Rainfall 239mm, being the rainfall site long term average
Evaporation 101mm
Transpiration 157mm
Runoff/drainage 0/27mm

Hence, growing season transpiration is 13mm + 157mm = 170mm

Growing season transpiration can be multiplied by water or transpiration efficiency which for a soil without any constraints in 20kg/mm/ha.

Therefore the potential yield for this soil type is 3.4t wheat/ha.

Soil water app graph example
Soil Water App of plant available soil water % and cover %

A nice aspect of the app is that it allows you ask questions on how the seasonal conditions are impacting on the soil water balance.

For example what if the crop was sown on sown 27 May 2017 but did not emerge until the 14 June 2017? What is the effect on soil water balance?

It only takes a couple of clicks to explore impacts of soil type or start condition changes on results, which can be compared by swiping between screens.

How DAFWA is integrating the information

The Regional Research Agronomy project is using local rainfall collected from a rain gauge which has Bluetooth capabilities.

This local rainfall data is added by selecting - add local rainfall.

These Bluetooth rain gauges linked to the SWApp are at several locations across the wheatbelt, on various soil types, including:

  • Salmon Gums – shallow sandy loam
  • East Wickepin - clay loam
  • South Stirling Primary School – sand over light clay
  • Katanning – sandy loam
  • Merredin – loamy clay
  • Tardun – red loam

The advantage of the Bluetooth rain gauges is that rainfall data at the local rainfall site is updated automatically, can be share with other users and requires less frequent visits to the rain gauge as these gauges store data.

It also requires less frequent visits to the rain gauge because it has the capacity to store the data.

The Regional Research Agronomy project is also using a series of focus paddocks to engage grower groups and growers with regionally important issues.

This involves monitoring a paddock at zone scale to observe changes over three growing seasons.

Activities include:

  • measuring soil moisture, nutrition and crop establishment
  • monitoring the paddock for disease, pests and weeds throughout the season 
  • measuring productivity in order to track seasonal conditions
  • determining the constraints that are present
  • examining crop response to management options
  • validating decision support tools such as the Soil Water App.

More information can be found at the Soil Water website  or contact David Freebairn, Soil Scientist, University of Southern Queensland on +61 (0)7 3161 8120.

For more information on the Soil Water App or the Regional Research Agronomy project please contact Stacey Hansch, Development Officer, Northam on +61 (0)8 9690 2168.

The Regional Research Agronomy project is also mentioned in Article 5 "New Development Officers to Build Capacity in Grains Research and Development" of this edition of AgMemo.