Aim: To investigate responses to phosphorus, nitrogen and potassium in wheat at Muntadgin

Key Messages:

  • With surface soil layer P at 25 mg/kg prior to sowing, addition of P fertiliser at establishment significantly increased wheat yield.
  • Similarly, N had a major impact on growth and yield, but K did not contribute to increasing yield at this site.
  • Maximum yield and gross margins was seen at N 40-60 kg/ha, with establishment P of 6 kg/ha.
  • Gross margin analysis suggests improved returns of between $50 and $100 per hectare can be achieved by choosing the most appropriate P and N rates.

Table 1. Soil Test Results

Depth NO3- NH4+ OC P PBI K S Cu Zn pH Al
0-10cm 25 1 0.51 25 32 57 22 0.70 0.39 5.1 0.6
10-30cm 9 1 0.25 18 47 55 17 0.80 0.26 4.9 0.5


A factorial trial design that included four rates of nitrogen,0, 20, 40 and 60 kg N/ha, and three rates of phosphorus, 0, 6, 12 and 18 kg P/ha with either 0 or 20 kg K/ha was established.



  Figure 1. Yield and protein response to N at different P rates with or without K applied.


Figure 2. Average yield response curves to P and N with or without K applied. 


  • In this trial the application of P and N significantly increased yield, the application of K had less of an impact.
  • Maximum yield and gross margins was seen at N 40-60kg/ha and P 6kg/ha, with K 20kg/ha providing a minimal increase.
  • Gross margin impact can be up to an additional $50 per hectare by selecting the optimal rate of P, and an additional $100 per hectare for optimal rate of N.
  • Adequate P nutrition is imperative, promoting early growth and vigour and setting up the crop to utilise applied N efficiently and gain maximum value from in season N applications.
  • K can improve yield response to both N and P and increase returns where circumstances are right.
  • The achievement of optimal productivity involves all nutrients and not an emphasis of a single one. Some of which, such as P, are only effective when applied at establishment so establishing good base nutrition at the start of the growing season allows the crop to take maximum advantage of opportunistic applications of in-season top up nutrients to which they will respond, such as N.