Wheat Yield Constraint Calculator: a tutorial

Page last updated: Tuesday, 23 May 2017 - 1:33pm

Please note: This content may be out of date and is currently under review.

Wheat yield constraint calculator is a simple tool to calculate yield potential and compare your paddocks performance over a number of years. To aid you in the use of the tool either follow the simple 'how to begin' guidelines or review the case study or view the YouTube video.

How to begin

  • Choose your location - to select a weather station's rainfall data:
    1. Click the town to activate the map with over 670 weather station locations;
    2. Select the weather station closest to your location on the map;
    3. Accept the location (button in the top right hand corner of map) to load rainfall data in the tool.
  • Choose your soil type to determine the average plant available water capacity (PAWC) of a soil:
    1. Click soil type to display a list of soils;
    2. If you are unsure, click the document icon for a description or;
    3. Click the MySoil tool link to identify your soil.
  • Estimates of water limited yield potential are displayed based on PAWC:
    1. A default PAWC is loaded when you select the soil;
    2. If you are aware of your soils PAWC, then adjust using the slider on the tool to the appropriate value.
  • Enter grain yield (t/ha) of your paddock to compare your crops performance:
    1. Wheat yields for the previous five years can be entered;
    2. Additional years can be added by clicking the 'insert new year' button.
  • Additional paddocks can be added:
    1. Click the 'new' button to add a new paddock;
    2. New location and soil type can be chosen.

Case study

A farmer in Coorow grew Mace wheat in 2010 and 2012 on a sandy brown earth. Yields were 1.64 tonnes per hectare (t/ha) and 1.84t/ha respectively. Mandelup lupins were sown in 2011 and yielded 1.2t/ha.

Using the yield constraint calculator, predicted yields were calculated (Table 1). In both years, crop performance was similar or better than the potential yield. Constraint was close to 100% which indicates good crop performance. Water use efficiency (WUE) was greater than 15 kilogramm per millimetre (kg/mm) of rain, another indication if good performance.

Table 1 Actual and potential yield of Mace wheat sown in Coorow on a sandy brown earth
Year Actual yield Potential yield Constraint WUE
2010 1.64 1.65 99.39 19.88
2012 1.84 1.53 120.26 24.12

What does it mean? The sustained good performance of the crop is an indication that both management and the soil resource are not limiting production of this paddock.


Information on the case study was provided by Department of Agriculture and Food, Western Australia's Focus Paddocks project (DAW213) which is supported financially by the Grains Research and Development Corporation.

Contact information

Art Diggle
+61 (0)8 9368 3563


Christine Zaicou-Kunesch