Field Research & Agronomy

Potassium Strategies

AIM

To assess the value of potassium (K) through drilling as a blend or compound and topdressing K at seeding time or after emergence on the growth and yield of wheat in the Ballidu area.

For further details on this trial contact your local Area Manager or research@summitfertz.com.au

BACKGROUND

K supply is increasingly important for maintaining optimal productivity of cropping country. Sandplain soils generally show low extractable K levels.
Potassium is often supplied as topdressed Muriate of Potash (MOP) before seeding, but this may not be the most effective method since the K may be pushed into slower-wetting inter-rows by seeding bars.
In this trial, we supplied K at different rates by topdressing MOP post seeding pre emergence (PSPE), four weeks after sowing (4WAS), drilled at seeding, or in a full NPK compound granule drilled at seeding with or without additional MOP.
We are examining effects on germination, early vigour and later grain production.

Decile 10 Summer rainfall was followed by a very dry growing season. Despite the dry winter, a soft finish in August and September provided respectable yields across the trial.

CONCLUSIONS

• Harvest yield and returns were maximised at 12 kg/ha of potassium.
• Early biomass suggested a response to 12 kg/ha of K but no improvement at higher rates. MOP drilled with the seed had a lower biomass than MOP topdressed or drilled in compound form.
• At harvest, there was a positive yield response to K at 12 kg/ha (200-400kg/ha) but no statistical difference between source or placement of potassium (p=0.05).
• Average gross margin response was $750 /ha at 12kg K/ha, whilst at higher potassium rates there was insufficient yield response to cover the extra fertiliser cost.
• At 24 kg/ha of K and above, MOP drilled with the seed had a negative impact on yield compared to the lower rates.