GRDC Precision Ag Research

Peter & Alison Groves

Optimising crop nutrition according to productivity zoned to evaluate if variable rate technology is likely to be profitable.

• The paddock was divided into high, medium and low productivity zones.

• Investigations were then undertaken to identify factors that may be limiting production in each zone.
• It was decided that investigating N, P and K rates across productivity zones would be the best option for 2002.

• The paddock was sown in strips which crossed the high, medium and low productivity zones.
• Each treatment was replicated 3 times.

• The yields of this trial were severely limited by drought (1.3-1.7T/Ha). April to October rainfall was 139mm, making 2002 a decile 1 season.
• The most economical treatment for all productivity zones in the trial site was the low fertiliser input.
• The low fertiliser input treatment had savings of $54 and $102 over the medium and high input treatments.
• In the high productivity zone of the biomass image it is clear that the high input treatments accumulated a higher biomass than the medium and low input treatments. However this additional biomass did not result in significant yield increase.

• In a very low rainfall season reducing fertiliser inputs can be the most economical strategy.
• Delaying nitrogen and potassium applications allows more strategic use of inputs.