Feeding the world’s growing population
New Zealand’s reputation as a quality food producer is growing.
The Fertiliser Association of New Zealand promotes and encourages responsible and scientifically-based nutrient management.
Research measuring the impact of soil fluorine
Former Massey University PhD student, Gere Thangavelautham, completed PhD research investigating the 'Impact of phosphate fertiliser derived fluorine on soil microbiology and white clover'
The Fertiliser Association has been actively supporting new young scientists and the development of research skills and capability in the arena of nutrient management for primary production. Studies like Gere's and the continued investment into developing our collective knowledge, skills and capability in agricultural science are essential, not just for New Zealand, but for the world's future security in food and fibre production.
Why is this PhD research important?
Rye grass clover pasture is still the mainstay of New Zealand pastoral 'grass fed' livestock industries. Phosphate fertiliser are applied to replenish the essential nutrient phosphorus, which is taken up from the soil and permanently removed by the sale of food and fibre. If not replenished, pasture production is reduced to at least half, and some cropping systems might fail completely. Fluorine (F) is the thirteenth most common element in the Earth's crust, and is found in the rock from which phosphate fertiliser is made. Fluorine is therefore found in phosphate fertiliser products applied to production land all over the world, and this study has examined the biological impacts of this additional fluorine applied to agricultural production land.
What was studied?
The most sensitive component of the Rye grass clover pasture system is considered to be the 'nitrogen fixing' bacteria, Rhizobium. These bacteria help to convert atmospheric nitrogen into a form of nitrogen which the plants can use. To assess the potential impact of soil fluorine on rhizobium, Gere investigated soil fluorine extraction methods for laboratory analysis of soil fluorine. Methods for assessing the (near) total amount of extractable soil fluorine were evaluated, and then also the amount that is considered to be freely 'available' to interact with soil microflora. Following the development of soil fluorine measurement techniques, respiration and inhibition assays were conducted to investigate the effect of soil fluorine on Rhizobium and the white clover.
What was found?
Results showed that microbial biomass and soil enzyme activities, and white clover growth and its interaction with Rhizobium, were not influenced by added fluorine - up to the highest concentration used in this study. The soil fluorine levels at which Rhizobium showed any sign of adverse effects occurred at levels much greater than occurs in New Zealand pastoral soils, reassuringly indicating there is no risk of adverse effects on soil Rhizobium and it activity in soil and plants.
This study also looked at the effects of managing soil acidity (pH) and also adding compost to reduce the bioavailability of soil fluorine. This showed that pH has a significant impact on 'adsorption' and 'desorption' of fluorine on the soil particles. Maximum adsorption occurred at pH of 5.5 - 6.8, meaning that adding lime to keep soil acidity within this range minimises the amount of soil fluorine available to interact with plants and soil microflora. The addition of compost also reduced bio-availability of soil fluorine. This is to be expected as it is now that fluorine is retained predominantly in the top-soil where it binds with organic matter and iron and aluminium oxides. However, the effects of added compost were not significant where soil pH was above 6.0.
Find out more
Read more about Gere's research here.
