Analysing New Zealand’s Agricultural Phosphorus Budget

An interest in farm sustainability and sustainable fertiliser management was the key driver behind Massey University student Theané de Klerk’s decision to focus her Master’s degree on New Zealand’s agricultural phosphorus budget.

Theané is one of three students that the Fertiliser Association of New Zealand (FANZ) is currently supporting as part of our commitment to developing New Zealand’s agricultural research capability on nutrient management.

Theané’s interest in agriculture was kick-started when she started secondary school.

“I was introduced to agriculture and horticultural science when I attended Mount Albert Grammar, with the school's eight-acre model farm providing up-close learning opportunities. I was initially drawn to farm and animal management and enjoyed helping the farm manager with daily farm tasks,” Theané said.

With a move to the Hawke’s Bay in her fourth year of high school Theané continued to study agriculture and horticultural science at Taradale High School.

“At Taradale, I became more interested in the environmental impact and sustainability side of the agricultural industry which is what inspired me to continue with this line of study at University,” she said.

Enrolling in Massey University, Theané took Soil Fertility and Fertilisers and Integrated Farm and Environmental Management papers which solidified her interest in farm sustainability and sustainable fertiliser management and lead to her decision to conduct her current research.

“Understanding the interactions of nutrients with the soil, and the plant/animal requirements for these nutrients is key to managing fertiliser application in a way that will increase production while still being economical and sustainable,” she said.

Theané’s research will provide data on the current phosphorus fertiliser usage in the agricultural industry and will develop a current soil phosphorus nutrient budget to understand how the current usage is influencing the soil P status. The budget will help identify the accumulation or depletion of P from our agricultural soils and help inform best practice P fertiliser recommendations for the wider industry.

“This research will analyse the soil phosphorus across industries, which means the current demands, current soil P budget and future demands can be applied across the agricultural sector rather than just to livestock, or cropping systems. Sustainable fertiliser use relates to the whole industry, not just dairy or wheat cropping, and so it is important to be able to create data that is useful to all,” she said.

“This research follows on from Mike Hedley’s work in 2011, where he looked at the P demand of the dairy, sheep and beef industries, and created a forecasted future use. We aim to use similar case study methods to look at the current P demand/use of agriculture across New Zealand, including a wider range of agricultural systems, and relating that to potential future demand and developing a national agricultural soil phosphorus budget. There has been some work in the UK to develop a nutrient budget for nutrients entering their main waterways and we hope to apply something similar, and slightly broader to New Zealand’s agricultural land,” she said.

Phosphorus's ability to accumulate in the soil profile affects how much fertiliser is required to maintain a target soil test level. As production has increased and agricultural systems have intensified, the level of fertiliser application has increased, and it is likely that the soil phosphorus balance has changed too. By producing a more up-to-date soil phosphorus budget, the national recommendations for application rate and optimal soil nutrient levels can be altered accordingly to consider the possible change in soil phosphorus in comparison to when the recommendations were first developed.

Theané’s first priority is to understand what the current phosphorus fertiliser demand is from the agricultural industry, as P fertiliser application makes up a significant proportion of phosphorus applied to farms. This will provide insight to the likely soil P status and the likely accumulation or depletion of phosphorus in our soils.

We will provide a further update on Theané’s findings at the conclusion of her research.

Theané’s research is funded by the Fertiliser Association of New Zealand. Her supervisor is Associate Professor Lucy Burkitt.