A rapidly growing world population has highlighted the need to significantly increase food production in the context of a world with accelerating soil and water shortages as well as climatic stressors. This situation has generated new interest in the application of liquid seaweed extracts because of their potent plant growth-enhancing properties through metabolic benefits, triggering disease response pathways and increasing stress tolerance. The basis for these benefits is complex and poorly understood. Liquid seaweed extracts are complex and have been demonstrated to possess novel mechanisms for increasing crop productivity. The benefits of seaweed extracts to crops have previously been reviewed in the context of the northern hemisphere, but not in the context of Australia, its crops and unique stressors. This review considers the application of seaweed extracts in Australian agriculture by (i) introducing the history of the Australian liquid seaweed extract industry and (ii) focusing on evidence of Australian research related to seaweed extract composition, plant growth properties during plant establishment, pathogenic disease and new approaches to phenotyping the biological efficacy of seaweed extracts. This type of research is essential for future Australian agriculture to develop effective strategies for the use of liquid seaweed extracts.

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This study investigated whether kelp extract from Durvillaea potatorum and Ascophyllum nodosum (Seasol Commercial w ) stimulates broccoli establishment and growth. Under controlled conditions in the glasshouse, weekly applications of kelp extract significantly increased the leaf area, stem diameter and biomass of broccoli by up to 70%, 65% and 145%, respectively. Also in the glasshouse, lower strength dilutions of kelp extract (1:200 to 1:500) were most effective in stimulating early growth of broccoli, whereas higher strength dilutions (1:25 to 1:100) were most effective later in plant development. In the field, application of kelp extract as a drench to a clay-loam soil (Sodosol) significantly increased the leaf number, stem diameter and leaf area of establishing broccoli seedlings by 6%, 10% and 9%, respectively, irrespective of application rate (three applications at 2.5 or 25 l ha 21 ). Furthermore, kelp extract significantly reduced the early incidence of white blister, caused by Albugo candida, on broccoli by 23%. In a sandy soil (Podosol), the effect of kelp extract was less pronounced, with only the leaf area of broccoli seedlings increasing significantly following treatment with kelp applied at the highest rate. It is hypothesized that differences in cation exchange capacity, organic matter and/or leaching properties contribute to variation in the response of broccoli to kelp extract in different soils. Future research is proposed to examine the capacity of kelp extract to offset the high nutrient inputs needed at establishment in the broccoli industry.

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Seaweed extracts are agricultural biostimulants that have been shown to increase the productivity of many crops. The aim of this study was to determine the effect of a seaweed extract from the brown algae Durvillaea potatorum and Ascophyllum nodosum as a soil treatment on the yield of wine grapes grown in Australian production and climate conditions. This study used a series of seven field experiments (2012–2017), across five locations, in three Australian states and four cultivars, and analysed data using a linear mixed model approach. The analysis revealed that recurring soil applications of the seaweed extract significantly increased wine grape yield by an average of 14.7% across multiple growing years that experienced climate extremes. Partial budget analysis showed that the use of the seaweed extract increased profits depending on the grape cultivar. This study is the most extensive investigation of its type in Australian viticulture to understand the effect of a soil-applied seaweed extract on wine grape production.