Estimating yield gaps in rainfed wheat caused by a nitrogen fertilizer deficiency in Western Australia in 2015

Chao Chen1, Noboru Ota1,

1CSIRO Agriculture and Food, PMB 5 Wembley, WA 6913,,


The size of the yield gap, defined as the difference between water-limited potential yield and farm yield, is often a result of a combination of management activities. A small yield gap implies that management is near optimum. Nitrogen (N) deficiency often limits crop yields and it is essential to understand its effect of N fertiliser on yield gap. This study assessed whether N fertiliser was deficient and limited dryland wheat yield in Western Australia in 2015, using the APSIM model and agronomic practices surveyed from 47 paddocks. The farm survey indicated that the N fertiliser applications ranged from 0 to 98 kg/ha, with 80% of surveyed paddocks applying less than 45 kg/ha. The simulated yield with N fertiliser applied on farm (farm yield) ranged from 1.9 to 5.7 t/ha with an average of 3.2 t/ha. The yield gaps due to N fertiliser deficiency ranged from 0 to 1.6 t/ha, with an interquartile range of just 0.6 t/ha. The range of the relative yield gap (expressed as yield gap % of water-limited potential yield) was from 0 to 34%, with only 2 out 47 paddocks having a relative yield gap > 30%. We concluded that wheat yield was not limited by N deficiency in the majority of surveyed farms in Western Australia in 2015 due high soil mineral N at sowing and mineralised N. However, there is still a potential to increase yield for paddocks that had higher potential yield through improved N fertiliser management.


The Australian Society of Agronomy is the professional body for agronomists in Australia. It has approximately 500 active members drawn from government, universities, research organisations and the private sector.

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David Marland Photography Southern Farming Systems Agriculture Victoria

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