Kelp as a plant growth stimulant

Kelp As a Plant Growth Stimulant

An ancient remedy to a modern problem

Seaweed has been used by farmers for hundreds of years to enrich soils and help crops thrive and survive stress. But with the advent of chemical fertilisers, and in a bid to meet the demands of a rapidly expanding population, many growers moved away from the ancient practice of using seaweed on their land. This modern reliance on synthetic fertilisers and nutrient mixes has led to water pollution, increased greenhouse gas emissions, loss in biodiversity, and increases in pest attacks [Refs 1,2,3]. These factors, combined with the rising price of chemical fertilisers, have led to renewed interest in the use of seaweed as a natural plant growth stimulant or ‘Biostimulant’. Some seaweed extracts have also been proven to help plants survive with less water, which is increasingly important given our warming climate and more widespread droughts. The science of creating seaweed biostimulants has now advanced to the point where the liquid extracts can be sprayed onto crops alongside other treatments, so they can be seamlessly integrated with modern farming practices.

Biostimulants are: “Substances and/or microorganisms whose function when applied to plants or the rhizosphere is to stimulate natural processes to benefit nutrient uptake, nutrient use efficiency, tolerance to abiotic stress, and/or crop quality, independently of its nutrient content.”

- European Biostimulants Industry Council

Backed by Science, loved by Nature

Scottish crofters would traditionally collect kelp washed ashore in winter storms, and spread it on the sandy soils where they grow barley and corn, or dig it into potato and vegetable beds. Liquid seaweed or seaweed ‘compost teas’ would also be brewed and sprayed on plants to enhance the quality of the crops.

This age-old tradition of using seaweed to boost yields and improve plant health is now backed by science, with reams of studies repeatedly documenting the beneficial effects of using seaweed [4,5]. Digging kelp meal into the ground creates a stable, well-structured soil with good organic matter content, a healthy population of soil microbes and trace elements, which are often lacking in chemical fertilisers. Liquid seaweed extracts also contain a mix of plant-based amino acids, growth hormones, plant protecting agents and minerals that are proven to help plants cope with stress such as drought and frost, recover more quickly from pest attacks, increase plant mineral uptake and nutrient efficiency, and promote cell division and growth [4,5]. This means that crops sprayed with liquid seaweed are typically bigger, greener, healthier, and more productive - resulting in a better yields and returns on investment.

“Biostimulant products can help farmers adapt their agricultural systems to an increasingly volatile climate while enhancing food production sustainability, thereby contributing to a climate-smart farm model for the future” -

- European Biostimulants Industry Council

More than just an NPK Fertiliser

Seaweed (and kelp) is not a ‘true fertiliser’ because it has a fairly low Nitrogen, Phosphorous and Potassium content (NPK) when compared to most other fertilisers. The nutrient content of seaweed is also not standardised because it is natural and organic. What makes seaweed effective is its high content of bioactive compounds and phytohormones that stimulate the natural processes of plants to enhance plant growth, nutrient uptake, plant quality and tolerance to stress, which all benefit plant yield and vigor.

Seaweed phytohormones

Seaweed extracts have high levels of natural plant growth hormones (phytohormones), especially auxins, cytokinins and gibberellins.

Cytokinins are important for new growth because they stimulate cells to divide rapidly and form new cell walls. They also work together with other plant hormones to enhance specific growth stages. For example, if cytokinins are applied during root formation, they will stimulate the division of more root cells. If cytokinins are applied during the vegetative growth stage, the plants will grow faster with stronger cell walls. And if cytokinins are applied just before fruiting and flowering they will stimulate more lateral buds to develop, which leads to better fruit and flower production.

Auxins stimulate root growth and have a positive effect on rooting (great for transplants), especially when cytokinins are also present. The bigger the roots the better the uptake of water and nutrients, which makes the plants healthier and more resistant to stress.

Gibberellins promote stem elongation and flower development, and also help seeds ‘wake up’ from dormancy. So seeds soaked in seaweed extract before planting tend to germinate faster and have better germination rates.

Providing an ecosystem service

Not only does seaweed help gardeners and farmers, it builds a more resilient and diverse ecosystem around the land. A wide range of wildflowers often grow amongst crops and gardens treated with seaweed, because they are not outcompeted by the vigorous plants grown with chemical fertilisers. These wildflowers support pollinating insects, that then attract predators such as hoverflies and ladybirds, which feed on crops pests [7].

“Only the whole seaweed extracts have been consistently proven to be very effective, which highlights the role of multiple components and their complex interactive effects on plant growth processes”

- Ali et al. (2021)

REFERENCES:

[1] Miguel A. Altieri, Clara I. Nicholls, and Marlene A. Fritz. (2005) Manage insects on your Farm, a guide to ecological strategies. Handbook series, Book 7. Published by Sustainable Agriculture Research and Education (SARE), pg 64-67. Impacts of Fertilizers on Insect Pests - SARE

[2] Menegat, S., Ledo, A. & Tirado, R. (2022). Greenhouse gas emissions from global production and use of nitrogen synthetic fertilisers in agriculture. Sci Rep 12, 14490. https://doi.org/10.1038/s41598-022-18773-w .

[3] Savci, S. 2013. Investigation of Effect of Chemical Fertilizers on Environment. APCBEE Procedia. Vol1: pg 287-292. https://doi.org/10.1016/j.apcbee.2012.03.047/

[4] Nanda, S., Kumar, G. & Hussain, S. (2022) Utilization of seaweed-based biostimulants in improving plant and soil health: current updates and future prospective. Int. J. Environ. Sci. Technol. 19, 12839–12852. https://doi.org/10.1007/s13762-021-03568-9

[5] Deolu-Ajayi AO, van der Meer IM, van der Werf A, Karlova R. (2022) The power of seaweeds as plant biostimulants to boost crop production under abiotic stress. Plant Cell Environ. Sep;45(9):2537-2553. https://doi.org/10.1111/pce.14391 . Epub 2022 Jul 19. PMID: 35815342.

[6] Ali O, Ramsubhag A, Jayaraman J. (2021). Biostimulant Properties of Seaweed Extracts in Plants: Implications towards Sustainable Crop Production. Plants (Basel). Mar 12;10(3):531. https://doi: 10.3390/plants10030531 . PMID: 33808954; PMCID: PMC8000310.

[7] Crofting for Wildlife, Seaweed as Organic Fertiliser. Machir Life+, 2014. ML-Seaweed-Advice-leaflet.pdf (machairlife.org.uk)