Farm advice: Liquid, suspension, or granular fertiliser

By: Dr Gordon Rajendram, soil scientist

Soil scientist Dr Gordon Rajendram takes a look at the different kinds of fertiliser available in NZ


Due to an increase in fertiliser costs, farmers are faced with keeping pasture or crop production at similar or higher levels but with similar fertiliser budgets to previously.

The question that arises then is whether we can keep the same fertiliser spend as previously and grow just as much nutritious pasture or more pasture without compromising production or have any detrimental effects on the environment?

This will be the first of a series of articles where I explore the above question.

Firstly, the main factors that drive pasture production are soil moisture, temperature, approximately 13 soil nutrients, soil acidity, microbiology, and soil air space (soil porosity).  The mantra I constantly use is "if you don’t test, you cannot manage".

It’s important to test soil, pasture, clover only, and individual crops to see if any of the above factors are limiting growth. 

All these parameters have optimum limits for pasture or crop growth and will be limited if these are not in the target areas.

For the 13 nutrients, once the optimum levels are reached, only maintenance rates are required and, therefore, application rates can be low depending on the nutrient, soil type, and climatic factors (leaching and runoff). Monitoring pasture growth rates is also an important testing tool.

In the last five years, I’ve had experiences with technologies that I believe can be part of achieving the above. In this article, I will concentrate more on my experiences with these technologies whereas, in the next articles, I will dwell more on the science.

A majority of fertilisers in New Zealand are applied in a solid granulated form for ease of spreading and generally are in a highly soluble form i.e., it becomes quickly available to pasture or crops. There are benefits to this, but once optimum nutrient levels are achieved, are there better technologies/modes of application available?

Suspension technology, or otherwise known as fine particle application or foliar/liquid, may be more efficient and cost-effective. Soluble liquid fertilisers can be applied with normal spray equipment but with suspensions require specialised equipment with robust pumps and larger nozzles.  

With liquids and suspensions, up to 16 elements (13 for pasture growth plus three more for animal health) can be applied in one application, including growth promotors, inhibitors and fungicides, or insecticides. Suspensions are in between liquid and granular and are ground-up fertilisers/nutrients and the rate of application can be as high as granular if required.


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