Review reveals no notable difference between fertiliser application methods

There are no significant differences between pasture production achieved using urea applied as a fine particle when compared to a granular form, a recent review has shown.

Led by Jeff Morton and commissioned by the Fertiliser Association of New Zealand, the review critically examined the results from 22 fertiliser trials, mostly conducted in New Zealand, from as far back as 1954.

“We were seeking to find out whether fine particle application fertilisers (FPA) are more effective than solid granular fertilisers in producing pasture dry matter,” says Jeff. “This was in response to the recent resurgence in FPA, especially in Southland – a method that has been touted as having agronomic and environmental advantages over other fertilisers.”

Granular fertiliser is solid, whereas FPA – an application method largely unique to New Zealand – involves grinding the urea, mixing it with water and applying it as slurry. FPA has been claimed to achieve a 40-50% higher conversion of nitrogen (N) to pasture dry matter than granular urea. This has been attributed to factors such as a more even distribution and the potential for FPA to absorb N directly through foliage, thereby minimising soil losses.

“In the research literature we mostly found no statistically significant difference in pasture dry matter yield when fertilisers were applied in these two different ways,” says Jeff. “We also looked at the literature on liquid fertilisers – where the urea is ground and dissolved in water – and found no difference there either.”

While two trials showed FPA to work better than granular fertiliser, both studies used mini plots or glasshouse pots, with higher rates of nitrogen. “Our explanation of why it was better in this method of experimentation compared with field trials was that they were pouring a lot of liquid onto a very small area of leaf so it wasn’t similar to what would happen in the field.”

Other field trials which showed some extra benefit when using FPA did not have any statistical analysis to support the results.

“Overall, there is insufficient experimental evidence to support the application of fertilisers in the FPA form over the traditional granular form. “

Economic and environmental comparisons between fertiliser types were outside the scope of the review.

The full research report has been published in the New Zealand Journal of Agricultural Research.