The effect of kelp extract on seedling establishment of broccoli on contrasting soil types in southern Victoria, Australia

Abstract

This study investigated whether kelp extract from Durvillaea potatorum and Ascophyllum nodosum (Seasol Commercial®) 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− 1). 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.