SUM20.16: Potassium and Phosphorus Rate Interactions for Wheat Production, Moorine Rock


Managing wheat nutrition in the eastern wheatbelt has implications for sustainable and profitable production. This trial investigates the interactions between increasing phosphorus (P) and potassium (K) interactions on wheat at a sandy loam site south of Moorine Rock. With hope to increase understanding and refinement of P and K application rates and importance in wheat yield and grain quality.

Trial Details

Location: Moorine Rock.

Trial Size: 2.2m x 10m, 12 treatments x 4 reps = 48 plots.

Soil Type: Sandy loam.

Crop Sown: Scepter Wheat, sown 2/05/2020 at 78kg/ha.

Season Rainfall: 286 mm, Moorine Rock DPIRD, 60 mm below long-term average.

Table 1: Pre-trial soil nutrient analysis.


Figure 1: Harvest yield (bars) and grain protein (lines) across four replicates. Yield increased with applied P, but K did not have the same affect.

Figure 2: Responses to P and Krate applications, positive yield response to increasing rates of P applied. Mitscherlich function fitted to both graphs

Figure 3: Return additional to average gross margin returns from control (P0 K0). Data shows addition of P increasing profits by approximately 49% at 18kg P/ha, while addition of K reduced profits to approximately 1.1% at 40kg K/ha.

Key Messages

  • Plant biomass significantly increased as rates of P applied increased, although higher rates of K did not have the same effect.
  • Yield increased with increasing rates of P but not K, ranging between 2.10t/ha and 3.24t/ha.
  • The most profitable treatment was 20kg K/ha and 18kg P/ha, returning $885/ha.
  • The trial data indicates there are significant increased profits to be made by small investments in establishing a strong foundation crop P status at sowing.

For further information about this trial please get in touch with local Area Manager Kobus Marais