What we analyse

Measuring and managing soil phosphorus levels (Olsen P) enables farmers to manage soil fertility in a manner that supports sustainable agricultural production and avoids unnecessary phosphorus use. This helps farm profitability and reduces environmental impacts. 

Fertiliser application is one of the largest single operating expenses for most farms. It doesn't make sense to apply fertiliser when it's not required to maintain soil fertility.

Routine soil tests

The member companies of the Fertiliser Association use almost 100,000 soil tests each year to inform and support good management practices with appropriate fertiliser recommendations.

Decline in phosphorus use

Phosphorus use in New Zealand has declined since peak levels in the early 2000s. The decline in use reflects build up in soil fertility, increased use of nutrient budgets, fertiliser costs, and increasing farmer awareness of good management and environmental responsibility, see here.

For total phosphorus use in New Zealand since 1990, see here.

Understanding soil phosphorus fertility across New Zealand

To better understand how soil phosphorus fertility is reflected across New Zealand's production land, the Association has examined routine soil Olsen P test results. Data comprises approximately 1,170,000 records from across New Zealand, covering a range of farm systems and soil types collected over a ten-year period from 2012 to 2022. 

More background and detail on fertiliser use in New Zealand farm systems can be found in our booklet series here.

Map of distribution of sampling

Density of Olsen P measurements across New Zealand based on postcodes for samples submitted. 

Table of samples by soil type

Summary of number of Olsen P soil sample records by farm type and region, included in the data set. (Note: A&F crops means arable and forage crops)