SUM20.15: Nitrogen x Phosphorus rates to support Spartacus Barley Production, Merredin


Assessing standard crop fertilizer practice against new strategies. This trial assesses the response of barley under a factorial nitrogen (N) and phosphorus (P) fertilizer application trial design in the Merredin area to increase recognition of the value of optimal N and P to barley yield, grain quality and profitable returns. The trial provides an important focal point for investigating P response, particularly, due to the soil P analysis indicating luxury soil P status at the surface (0-10 cm) but deficient below.

Trial Details

Location: Merredin

Trial Size: 2.2m x 10m, 16 treatments x 4 reps = 64 plots.

Soil Type: Clay loam.

Crop Sown: Spartacus Barley, sown 13/05/2020 at 77kg/ha.

Season Rainfall: 212 mm, BOM Millston, 18 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.

Figure 2: All yield response curves to N and P rate applications. There was a strong response to N and a weak response to P. Mitscherlichfunction is fitted to each dataset.

Figure 3: Grouped mean gross margins for applied N and P. Optimum returns came from 25kg N/ha and 6kg P/ha.

Key Messages

  • Plant growth significantly increased with increasing rates of N, but not P.
  • Yields increased with increasing rates of N but not P, ranging between 1.84t/ha and2.72t/ha.
  • The most profitable treatment was 6kg P/ha and 50kg N/ha, returning $610/ha.
  • The trial data indicates thatthere are significant increased profits to be made by a small investment in establishing a strong foundation crop N and P status at sowing.

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