SUM20.23: Apex Yield Series – High end Nitrogen, Phosphorus and Potassium Rates for Wheat, Corrigin


Summit have instigated a trial series to allow maximum yield potential expression of contemporary crop varieties by removing all nutrient limitations. This trial investigates the interactions between nitrogen (N), phosphorus (P) and potassium (K) rates on Scepter wheat grain production at a sandy clay loam site north west of Corrigin, with aims to challenge old-school conventions of nutrition standards.

Trial Details

Location: Corrigin.

Trial Size: 2.2m x 10m, 30 treatments x 3 reps = 90 plots.

Soil Type: Sandy Clay Loam.

Crop Sown: Scepter Wheat, sown 30/04/2020 at 85kg/ha.

Season Rainfall: 188 mm, Corrigin DPIRD, 64 mm below long-term average.

Table 1: Pre-trial soil nutrient anlaysis.


Figure 1: Individual treatment yield (bars) and protein (lines) presented as the mean of 3 replicates. a) Yield and protein response to increasing N and P rates at no K. b) Harvest and protein response to increasing N and K rates when 16kg P/ha was applied at seeding.

Figure 2: All yield responses to N and P rate applications, positive yield responses to increasing N and P rates. Data is from treatments with Nil K applied. Mitscherlich function fitted to all datasets.

Figure 3: Returns additional to average gross margin from control (N0 P0 K0). Data shows addition of N and P increasing profits to a point, while K rates greater than 20kg K/ha provided no economic benefit.

Key Messages

  • Increasing N rates significantly affected plant vigour at both assessment times, with the earlier time of assessment also affected by P rates.
  • Yield and protein concentrations were both significantly affected by N and P rates, with K having no significant influence.
  • Yield ranged between 2.55t/ha and 4.51t/ha.
  • The most profitable treatment was with 16kg P/ha, 60kg N/ha and 20kg K/ha returning $1095/ha.
  • Returns additional to nil control for increasing P rates was maximised when 16kg P/ha was applied, with a return of 26%.

For further information about this trial please get in touch with local Area Manager Steve Cooke,