INTRODUCTION

In recent years there has been renewed interest in the use of seaweed extracts as a fertiliser within Australian agriculture (Arioli, et al., 2015). As well as containing a range of macro‐nutrients seaweed extracts also contain plant hormones and natural growth regulators which can potentially act as crop bio‐stimulants (Panda, et al., 2012).

However, since seaweed is a natural product, plant hormone concentrations within it may vary considerably, and may only be short lived. Seaweed extracts can produce real benefits to growers, but it’s important for a grower to understand the properties of any product they are using in order to get the best out of it.

Two leading seaweed based liquid fertilisers Microbe Plus® Kelp (M+Kelp) and Seasol are assessed in terms of their plant hormone content and bio‐stimulant effect. The potential benefits of using each are discussed below. M+Kelp has been created via a unique process that blends and digests high grade seaweed species with plant beneficial microbes, fungi and bacteria and selected plant nutrients to create an excellent fertiliser.

Seasol is derived from different seaweed species. Both the botanical family1 and the environmental factors affect the composition and concentration of the different hormones and other biostimulants in different seaweeds. That’s why the efficacy of the different products when used as plant fertilisers may vary.

What are plant hormones and why are they important?

Plant hormones are nature’s way of controlling plant growth and development, they are also essential in helping plants adapt to environmental stress. They act as chemical messengers, and help to regulate the plants physiological processes. Plant hormones fulfil essential roles in cell differentiation, and it is well established that plant hormones can initiate primary growth and morphogenesis or the development of the plants form. Plant hormones also play a crucial role in helping plants adapt to environmental stress, e.g. for drought by stimulating stomatal closure to reduce water loss (Peleg & Blumwald, 2011). Plant hormones are also involved in regulating the uptake of nutrients and the response to infection by pathogens (Argueso, et al., 2009).

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