Field Research & Agronomy

Potassium strategies and phosphorus response in wheat

AIM:

‍To determine the optimal strategy and form for applying potassium fertiliser in wheat in the Borden area, whilst also investigating phosphorus response.

For more details about this trial contact your Area Manager or Summit's Research Team

KEY MESSAGES

• Biomass measurements mid-season indicated a strong response to P and K fertiliser and an amplified response where K was supplied in compound form.
• At harvest, a significant yield response to K was measured but no significant difference between source or placement of K was measured.
• Higher P rates stimulaBorden ted greater biomass and advanced maturity, which was detrimental during early frost events, resulting in a negative yield response to P at harvest.
  

As a result of the moist sowing conditions, early sowing date and sandy soil; this trial was more advanced than the surrounding paddock and other crops in the region, posing a greater risk of damage from earlier frost events.
During field tours in August, some signs of frost damage were apparent across the trial and was confirmed at harvest with lower than expected yields.
Interestingly, there was a negative yield response to P despite the large biomass response measured during the growing season.
Higher P rates advanced to maturity more rapidly, which may have been detrimental during early frost events where flowering heads were susceptible.

CONCLUSIONS

• Biomass measurements mid-season indicated a strong response to phosphorus and potassium fertiliser and an amplified response where K was supplied in the compound form.
• At harvest, a significant yield response to K was measured but no significant difference between source or placement of K was measured.
• The highest yielding treatment of 3.88 t/ha was generated by 10P with 20K as MOP topdressed  IBS, which was an 860 kg/ha improvement compared to 0K.
• Higher P rates stimulated greater biomass and advanced maturity, which was detrimental during early frost events, resulting in a negative yield response to P at harvest.
• Under these conditions, yield and returns were maximised at 20 kg/ha of K and, due to the frost effect, nil P.
• Considering the biomass response to phosphorus during the growing season and yield results from other trials in the area, between 12-15 kg/ha of P would be close to maximising yield and returns without frost damage. A repeat of this trial sown later in the season to limit frost risk would be valuable to determine optimal P rates to maximise grower returns.