The Sirius Wheat Calculator

September 2005
The Sirius Wheat Calculator and Potato Calculator software programmes were designed as an interactive decision support tool growers can use to manage nitrogen fertilizer and water in wheat and potato crops. The programmes provide rules for the grower to gain the optimum yield from their crop while minimising the amount of nitrogen leached.

Following increasing public scrutiny about nitrogen applications and their affect on groundwater leaching the model is believed to have excellent potential for environmental monitoring. The programme has taken three years to design and has received funding support from the MAF Sustainable Farming Fund, FAR, Balance Agri-Nutrients and has been developed by Crop and Food Research. Funding for the programmes end in 2005 and seminars will be held shortly in an attempt to encourage farmers to use the software and help decide about the future direction.

So how do the programmes work?

The factor that makes the programmes stand out is the work Crop and Food Research have done to ensure the software matches the regional variations within an area. For example, once a soil mineral nitrogen test is conducted growers are able to input cultivar, soil type and sowing dates data before accessing localised recent weather records including future forecasts. This data means the model can accurately estimate when either nitrogen or water supply is limiting. The programmes can then generate a schedule of applications that can be adjusted interactively, in some cases by delaying application dates or altering application amounts.

Subtly making changes to a nitrogen regime can make a large difference to the bottom line in a wheat crop and in one case has made a $6000 saving for a farmer who trialled the programme. The wheat calculator has matched input requirements in irrigated feed wheat crops very closely with both protein levels and crop yields accurately predicted.

For both programmes deep sampling farm soil nitrogen levels down to 80cm remains an important success factor with a $45 test saving growers up to 100kg nitrogen per hectare.

The programme was tested by a group of around 20 Canterbury farmers who have commented that it became a tool they felt they couldnt do without.

Potato growers in particular have benefited as they often have large residuals of nitrogen left over once the crop is harvested due to incorrect calculations on when the nitrogen was needed. One farmer had 325kg/ha nitrogen left behind that could have supplied all the nitrogen requirements of the wheat crop that followed. Instead further applications followed which would have been avoided by using the wheat calculator.

The calculator attempts to leave as little residue behind as possible, which is beneficial in a time when many regional councils around New Zealand are looking to impose restrictions on nitrogen applications.

Thanks to: Rob Zyskowski (modeler/program developer) and Tabitha Armour ( FAR)

Crop and Food Research, Private Bag 4704, Christchurch.