SUM20.17: Nitrogen x Phosphorus Rate Interactions in Winter Wheat (Illabo), Muntadgin


Winter wheats show promise as a management tool for grazing and grain, and is advantageous in early sowing conditions. This trial investigates the interactions between increasing nitrogen (N) and phosphorus (P) interactions on Illabo wheat. At a sandy loam site south east of Muntadgin we aim to improve understanding of N and P importance in yield and grain quality and begin to elucidate nutrient response behaviour in winter wheats with their distinct growth habits.

Trial Details

Location: Warakirri Mawarra, Muntadgin

Trial Size: 2.2m x 10m, 23 treatments x 4 reps = 92 plots.

Soil Type: Sandy loam.

Crop Sown: Illabo Wheat, sown 20/03/2020 at 82kg/ha.

Season Rainfall: 178 mm, Muntadgin East 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 N and P.

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

Figure 3: Grouped mean gross margins for applied P and N. Optimum returns come from 60kg N/ha and 18kg P/ha when MAPSZC was applied.

Key Messages

  • May storm surface water movement caused both burial of seed and erosion and combined with difficult seeding depth control on the ripped and ploughed soil, contributed to low emergence.
  • Applying AllRich as a P source at 6 and 12kg P/ha significantly affected emergence, N concentration and P concentration.
  • Plant vigour significantly increased as rates of P applied increased, but profile moisture limited the effect of higher rates of N.
  • Yield increased with increasing rates of both N and P, ranging between 2.19t/ha and 3.32t/ha.
  • The most profitable treatment was 60kg N/ha and 18kg P/ha, returning $850/ha.
  • Illabo has significant yield potential for the region that should be supported by sufficient nutrition but monitoring protein may need consideration.

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