People have been growing with kelp for centuries though not necessarily with the idea of using it as a growth supplement. It contains a lot of gelatinous compounds (alginates) which when used on sandy soils improves the texture and water retention by essentially gluing the particles together. There is a lot of risk in the processing of this method however since insufficient rinsing in fresh water will add salinity to the soil and too much will wash away the alginates. Furthermore, earthworms which are important in a healthy soil can be inhibited by kelp in higher concentrations.
What is Kelp?
Also known as brown algae, it is a very diverse group of simple plants living in the oceans. The types that we're interested in grow as thick forests in the shallow coastal areas in many places in the world. These are ecologically very important areas with high levels of biodiversity.
In addition to being useful in agriculture it is important in many Asia cuisines and alginates are widely used in processed foods as thickeners.
Kelp as Fertilizer
While most commonly used as a supplement, kelp can also be used as a fertilizer usually having around an NPK value of 0.3 - 0.1 - 1 with additional trace elements. It can be difficult to generalize however, since there's a wide variation of quality between species and locations.
Used in this way, there's minimum processing. It is washed to get rid of the high levels of sodium and then dried and ground up before being spread onto the soil.
Kelp as a Biostimulant
There is additional processing done when the product is going to be used as a stimulant. First of all most of the biomass contained in kelp is in the form of fibre and so rather than being dried the kelp is pressed instead which extracts the water soluble components.
This extract is rich in:
Phytohormones - With smaller traces of auxins an gibberellins, the most significant being cytokinins. These act as signaling compounds for cell division in the shoot and regulate bud growth.
Vitamins - Unlike animals plants produce their own vitamins, however providing additional ones will provide the plant with a short cut so will not have to produce its own. Typically kelp based biostimulants will also add additional thiamine (B1) as this will provide extra resources for the plant when dealing with stressful situations like drought or frost.
Carbohydrates, Enzymes, and Amino Acids - Here again the plant will synthesize these compounds all on its own but giving these as a supplement will give the plant a short cut so its resources can be used elsewhere.
Along with fulvic acid, kelp extract is one of the most powerful biostimulants available. It does differ from fulvic (which is mined) in that it is a renewable resource. If managed properly can be a sustainable source of food, raw ingredients, soil builder, fertilizer, and biostimulants will into the future.