The past few years have been a tumultuous time for international markets, with the COVID-19 pandemic and political instabilities. Global supply chains – including the supply of fertiliser and agricultural labour – have been disrupted, with prices rising substantially.

Yet, a recent survey of growers in Western Australia has shown that agronomy remains the most-important factor driving nitrogen fertiliser decisions.

The results demonstrate that growers place a strong emphasis on balancing seasonal soil moisture and yield potential alongside the long game of maintaining soil fertility.

The survey, which was designed to better-inform future GRDC investments that support fertiliser decision-making, was undertaken by the University of Western Australia and the Western Australian Department of Primary Industries and Regional Development as part of a GRDC investment led by Murdoch University through the SoilsWest alliance.

It will also enhance the decision-making capacities of growers and advisers by unpacking the drivers behind decisions that are often made intuitively.

Driving decisions

In September 2020, 425 grain businesses from WA were interviewed by telephone to enable researchers to better understand the factors that influence growers’ nitrogen fertiliser decision-making. The 83 per cent of participants who had been farming 10 to 15 years ago were also asked to reflect on their past practices.

Their responses were analysed to determine which factors played the most-important role in key decisions.

Drivers were categorised as:

• agronomic – drivers that affect crop production and soil sustainability, including rainfall, crop type and sequence;
• logistical – the organisation of farm operations, including capacity of management, labour, storage and machinery; and
• socio-economic – growers’ aims and approach to risk, budget and prices for fertiliser and grain.

In general, the agronomic drivers of rainfall and reaching yield targets had the biggest impact on growers’ fertiliser programs.

One of the main changes over the past 10 to 15 years has been the increase in the number of nitrogen applications to better match nitrogen inputs to seasonal conditions. Whereas respondents typically applied nitrogen once or twice a year 10 to 15 years ago, now they are more likely to apply it two to three times, with some growers applying nitrogen up to five times.

Season-dependent nitrogen applications are expected to continue to increase in importance compared to fertiliser applied at seeding as growers adapt to rainfall variability and seek to streamline sowing operations to manage larger farm sizes and more-complex cropping programs.

Price isn’t everything

The influence of socio-economic drivers such as budget constraints and fertiliser prices has declined over the past 10 to 15 years. This can in part be attributed to a trend of increasing farm business profitability over the same timeframe.

Over the past decade, nitrogen fertiliser prices have plateaued. However, the recent spike in fertiliser prices is an example of how socio-economic issues can play a big role in the short-term. Fertiliser price was not found to play a significant role in decision-making in this survey; however, it was undertaken before nitrogen prices began to rise sharply.

In keeping with global trends, the survey showed an increase in the average nitrogen rate from 48 kilograms of nitrogen per hectare to 60kg/ha over the past 10 to 15 years.

Global trends likely to influence agriculture, and therefore fertiliser use, over the coming decade include political impacts on trade, climate variability, carbon accounting and innovations in productivity and technology.

More information: Dr Liz Petersen, 0404 077 194, liz.petersen@uwa.edu.au