Gee, I love Algae! — An Exploration of Seaweed Fertilizers

Though the earliest relatives of the seaweed plant dates back to more than 1.6 billion years ago, it remains one of the most versatile plants of the modern world (Osterloff 2017). “Seaweed” is the common name used to classify large, multicellular algae. Among the years, its applications have evolved— from being known as a gastronomical treasure back in ancient times, to modern plastic alternatives. The subject of this post is another important hallmark in the creation of sustainable alternatives– seaweed fertilizer. 

A fertilizer can be classified as “a natural/synthetic material used to supply essential nutrients for plant growth” (Macmillan et al. 2025). The Haber-Bosch process, invented in 1909, earned scientists Fritz Haber and Carl Bosch a Nobel Prize (Smith et al. 2020) and catapulted the production of nitrogen fertilizers. These are a type of Chemical Fertilizer (CF), which are manufactured fertilizers that generally contain higher concentrations of macronutrients essential for plant growth, such as nitrogen, potassium and phosphorus. Seaweed fertilizers function similarly by providing plants with these macronutrients, in addition to “rare elements (such as zinc, bromine, and iodine) which are unique to marine organisms” (Meng et al. 2022). Their administration differs from CFs, as they do not directly supply nutrients to crops, instead introducing cultures of bacteria and fungi which integrate them into the soil (MR Wahane et al. 2020). 

A fertilizer can be classified as “a natural/synthetic material used to supply essential nutrients for plant growth” (Macmillan et al. 2025). The Haber-Bosch process, invented in 1909, earned scientists Fritz Haber and Carl Bosch a Nobel Prize (Smith et al. 2020) and catapulted the production of nitrogen fertilizers. These are a type of Chemical Fertilizer (CF), which are manufactured fertilizers that generally contain higher concentrations of macronutrients essential for plant growth, such as nitrogen, potassium and phosphorus. Seaweed fertilizers function similarly by providing plants with these macronutrients, in addition to “rare elements (such as zinc, bromine, and iodine) which are unique to marine organisms” (Meng et al. 2022). Their administration differs from CFs, as they do not directly supply nutrients to crops, instead introducing cultures of bacteria and fungi which integrate them into the soil (MR Wahane et al. 2020).

In terms of efficacy, the organic extract promotes growth through an improvement in soil quality and moisture retention. Along with this, they also contain probiotics which possess enzymes such as sucrase and cellulase (involved in polysaccharide degradation), as well as nitrogen-fixing capabilities. Long-term application has been shown to decrease the content of pathogenic bacteria within soil (Qiqin et al. 2023).

Figure 1: An illustration of the effects of applying the fertilizer into surrounding plant soil, leading to increased nutritional uptake, decreased pathogen content and other effects mentioned above (Qiqin et al. 2023)

Figure 2: Results of (Pei et al. 2024) which show that the application of a seaweed fertilizer exhibited an average increased crop yield of 15.17% compared to a non-fertilizer control group.

In comparison to CFs, seaweed fertilizers have a slower effect on the soil. However, why are so many green farmers opting towards using them?

The overuse of CFs can result in unseen and undesirable effects on soil health. Many CFs contain traces of heavy metals which can enter the food chain to cause “low birth rate, congenital disabilities, and cancers” in humans (T. and M.a. 2023). Another common phenomenon associated with the overuse of chemical fertilizers is known as Nitrogen Leaching. This is the process where “nitrate (NO₃⁻) anion[s] moves downwards in the soil profile with soil water” (Padilla et al. 2018). In turn, excessive use of CFs can contaminate the ground water and harm animal populations. Maintaining the health of soil is important, as overuse of CFs can lead to more costly consequences in the long-run when the soil becomes no longer viable for use. 

New innovations in green technology are popping up every day, allowing us to conserve resources for future generations to come. Despite our reliance on chemical fertilizers for centuries, there is still time to pivot to more sustainable alternatives. After all, seaweed is (quite literally) greener!

References

Macmillan, S. R., R. A. Hedlin, Tom Jensen, and Cynthia Grant. 2025. “Fertilizer.” Thecanadianencyclopedia.Ca. https://thecanadianencyclopedia.ca/en/article/fertilizer.

Meng, Cuiping, Gu Xue, Haiyan Liang, et al. 2022. “Optimized Preparation and High-Efficient Application of Seaweed Fertilizer on Peanut.” Journal of Agriculture and Food Research 7 (March): 100275. https://doi.org/10.1016/j.jafr.2022.100275.

MR Wahane, NA Meshram, SS More, and NH Khobragade. 2020. “Biofertilizer and Their Role in Sustainable Agriculture-A Review.” The Pharma Innovation Journal 9 (7): 127–30. https://www.thepharmajournal.com/archives/?year=2020&vol=9&issue=7&ArticleId=4846.

Osterloff, Emily. 2017. “Seaweeds: A Hidden Habitat Under Threat.” Nhm.Ac.Uk. https://www.nhm.ac.uk/discover/seaweeds-a-hidden-habitat-under-threat.html.

Padilla, Francisco M., Marisa Gallardo, and Francisco Manzano-Agugliaro. 2018. “Global Trends in Nitrate Leaching Research in the 1960–2017 Period.” Science of The Total Environment 643 (December): 400–413. https://doi.org/10.1016/j.scitotenv.2018.06.215.

Pei, Baolei, Yunpeng Zhang, Ting Liu, et al. 2024. “Effects of Seaweed Fertilizer Application on Crops’ Yield and Quality in Field Conditions in China-A Meta-Analysis.” PLOS ONE 19 (7): e0307517. https://doi.org/10.1371/journal.pone.0307517.

Qiqin, Liu, Zhou Huaguang, Sun Minxiu, et al. 2023. “Improvement of Soil Structure and Bacterial Composition by Long-Term Application of Seaweed Fertilizer.” Journal of Soil Science and Plant Nutrition 23 (4): 5122–32. https://doi.org/10.1007/s42729-023-01341-0.

Smith, Collin, Alfred K. Hill, and Laura Torrente-Murciano. 2020. “Current and Future Role of Haber–Bosch Ammonia in a Carbon-Free Energy Landscape.” Energy Environ. Sci. 13 (2): 331–44. https://doi.org/10.1039/c9ee02873k.

T., Karthik, and Jayasri M.a. 2023. “Systematic Study on the Effect of Seaweed Fertilizer on the Growth and Yield of Vigna Radiata (L.) R. Wilczek (Mung Bean).” Journal of Agriculture and Food Research 14 (December): 100748. https://doi.org/10.1016/j.jafr.2023.100748.