SUM20.02: Potassium Rates, Source and Placement, Year 1, Wheat, Badgingarra


Progressively increasing K rates to optimise returns poses questions of contemporary crop tolerance to chloride (Cl-) associated with muriate of potash (MOP) compared with sulphate of potash (SOP) sources. This trial assesses the importance of K placement as either MOP or SOP, on wheat in 2020, at a sandy site east of Badgingarra at rates designed to run-down, maintain and potentially build K soil reserves over time.

Trial Details

Location: Badgingarra.

Trial Size: 2.2m x 10m, 18 treatments x 3 reps = 54 plots.

Soil Type: Sand

Crop Sown: Ninja Wheat, sown 08/05/2020 at 88kg/ha.

Season Rainfall: 292 mm, BOM Bungulla, 86 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 N and P.

Figure 2: Comparison of MOP and SOP K rate applications as an average across different placements on the harvest yield. SOP had a stronger yield response to increasing K rates than MOP.

Figure 3: Returns additional to average gross margin from nil control (nil K). Data shows a greater return from banding the fertilizer with the seed.

Key Messages

  • Plant growth significantly increased with the interaction between K source, rates and placement.
  • Yield averaged 3.6t/ha, MOP produced higher yields when banded below the seed while SOP out yielded MOP when banded with the seed.
  • Protein averaged 11.3% and the greatest treatment differences were seen when fertilizer is banded below the seed, with MOP producing higher protein than SOP.
  • The most profitable treatment was banding 30kg K/ha MOP with the seed, returning $1,060/ha.
  • There is a 12% higher return additional to nil fert when 30kg K/ha MOP is banded with the seed, and a 16% loss when 75kg K/ha SOP was banded below.

For further information about this trial please get in touch with local Area Manager Brett Beard,