Imported phosphate for fertiliser is expensive – could this homegrown alternative be a solution?

Fyletto/Getty Images Since the end of the second world war, adding phosphorus to soils in the form of mineral fertiliser has played a crucial role in increasing and maintaining global food production in response to population growth.

However, plants only take up 20-50% of the phosphorus from fertiliser applications.

The unused phosphorus is mainly stabilised through chemical reactions which bind it to soil minerals.

It accumulates as “legacy soil phosphorus”, with an increased risk of contributing to water pollution.

In New Zealand, phosphorus for fertilisers is manufactured exclusively from imported phosphate rock.

But there is an alternative to using rock-based phosphorus.

Struvite is a phosphorus-rich compound that can be recovered from wastewater treatment processes.

As our research shows, struvite raises phosphorus uptake by plants and may reduce transfer to waterways.

It could at least partially replace conventional phosphorus fertilisers.

A field fertilised by struvite.

Florencia DeLucca Agrelo/Lincoln University , CC BY-SA Recovering phosphorus from waste A combination of factors has resulted in significant cost increases for mineral phosphorus fertilisers , while economic and geopolitical instability disrupted supply chains and caused further price volatility.

For example, after decades of relative stability, the cost of single superphosphate has doubled in price from NZ$200 to $400 per tonne since 2000, with notable spikes in 2008 ($480 during the Global Financial Crisis), 2022 ($500 at the start of the Russian invasion of Ukraine) and 2026 ($550 because of Middle East conflicts).

It is widely acknowledged that we need to improve the efficiency of phosphorus use in primary production systems .

This can be achieved by using different plants in crop and grassland systems to enhance uptake from fertiliser and legacy soil phosphorus, and by recovery and reuse of phosphorus from waste.