Liquid, Suspension or Granular Fertiliser, which is better?

Waikato-based Soil Scientist Gordon Rajendram PhD is considered one of New Zealand’s experts in soil fertility. He is committed to helping New Zealand farmers get the most out of their soil so that their farm can work more proficiently and be sustainable while still increasing farm profitability. Dr Gordon Rajendram formerly worked at AgResearch, Ruakura Research Centre, Hamilton.  He has developed two fields of calibrated soil tests (N & S) which are used for agronomic advice in New Zealand and his industry-leading work on leaching has been included in the Overseer nutrient model.

Due to the increase in fertiliser costs, farmers are faced with keeping pasture or crop production at similar or higher levels with similar fertiliser budgets to previously.  Can we, therefore, 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 to the environment?

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

Firstly the main factors which drive pasture production are soil moisture, temperature, approximately 13 soil nutrients, soil acidity, microbiology and finally but not least soil air space (soil porosity).  

The mantra I constantly use “if you don’t test, you cannot manage”.  It is very 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 of pasture growth rates is also a very important testing tool.

In the last five years, I have 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.

The majority of fertilisers in New Zealand are applied in a solid granulated form for ease of spreading and generally are a in a highly soluble form i.e., 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 rate of application can be as high as granular if required.

So, how can these technologies be more efficient and cost-effective? These questions will be answered in following articles.