Potential yield tool

Growing season rainfall is composed of cumulative rainfall at the time the tables are produced plus decile rainfall finishes for the remainder of the growing season.

Rainfall deciles are generated from years 1975 to the year prior to the growing season of interest.

The potential yield model assumes that:

• crop emergence occurs in April or May
• the timing of rainfall during the season does not negatively affect crop growth (there is no drying off)
• there are no soil constraints that hinder root growth.

If any of these assumptions are not met, then potential yield could be considerably lower than shown in the tables.

While potential yield estimates can help create a narrative for the progress of a crop and aid key in-season decision-making, other key factors also need to be considered to arrive at an accurate picture. These include:

• soil status and characteristics including stored soil moisture, soil water-holding capacity and any barriers to infiltration
• stored nitrogen and other nutrient availabilities
• factors such as non-wetting, water-logging through topography or impermeable layers, leaching or dispersible clays in the soil.

The timing and event intensity of rain during the growing season can also greatly influence the conversion of rainfall to biomass and yield.

To use the tool, first select a weather station from the drop-down list below.

Next, select the summer start date. Usually, the start of summer is set to 1 November of the year prior to the current growing season. This can be changed, for example, if a large rainfall event occurred in early November that is unlikely to affect the soil moisture status at the end of summer then you may set the summer start date to exclude that event. The start of summer must be before the start of the growing season. The end of summer will be automatically set as the day before the growing season starts.

Now select the growing season start and end dates. Usually, the growing season is set to be from 1 May to 31 October. However, some growers may find 1 April to 30 September to be more appropriate depending on their location. The growing season start and end dates must be within the same calendar year.

Potential yield for the current growing season is calculated using the forecast date. Growing season rainfall must be known up to the forecast date, projected decile finishes are used to forecast growing season rainfall after the forecast date. During the growing season, the forecast date is usually set to the current date.

How the model works

The default start to summer is 1 November of the previous year to the growing season. The default growing season in April to October. These dates may be modified  to suit the grain growing season at a location and for a given season.

Different combinations of WUE and Evaporation may be used to give estimates of potential yield in different situations. For instance, WUE tends to increase from north to south across the grainbelt, and from lower to higher rainfall areas. Typical combinations include:

Typical combinations of WUE and evaporation.

Situation	WUE (kg/ha/mm)	Evaporation (mm)
Normal season (decile 4, 5, 6) deep sandy duplex and loamy earth, warm finish.	15	110
Wet season (decile 7, 8, 9), deep duplex, loamy earth and deep well structured clays, stored water from summer or very good spring rain.	20	110
Normal season (decile, 4, 5, 6, 7), duplex soils, cool finish with better rain in spring.	15	90
Dry season (decile 1,2), soil with low water holding capacity give up water easily, late emergence or very poor early growth, warm spring.	12	110
Dry season (decile 3), shallow soil or soil with low water holding capacity, late emergence or very poor early growth.	12	90

Maps of potential yield are displayed as part of the Department of Primary Industries and Regional Development's Seasonal Climate Information [1] tool.