Promising results on the use of seaweed discards as a fertilizer and protective agent against downy mildew


The ALGATERRA project is coming to an end. After more than two years of work, in which the entities participating in this project, led by the company PORTO-MUIÑOS S.L., have worked on the development of new fertilizers and biostimulants based on algae extracts, it can be concluded that the results achieved are encouraging.

ALGATERRA was born with the aim of developing new agricultural inputs from discards from the processing of algae for food use, which could be used both in organic farming and in sustainable conventional agriculture, so that from these discards a new added value for high quality organic resources would be generated.

For several years, Spain has been leading the organic farming sector in Europe, devoting a large area of land to this type of crops. The inputs used in this type of agriculture must overcome two important handicaps: they must comply with current regulations and be easily accessible to farmers in the sector. In this sense, and based on the extensive experience and tradition that the farmers of the Galician coast have, regarding the use of such a natural and ecological resource as seaweed applied as fertilizer in their plantations, the idea of the ALGATERRA project was born.

Some of the seaweed species selected for this project were wakame (Undaria pinnatifida), sea lettuce (Ulva rigida) or kombu (Laminaria ochroleuca), belonging to different groups of algae with very different properties, and which come from the discards of the PORTO-MUIÑOS company’s production processes: sea lettuce (18 tons/year), wakame (16 tons/year), sea moss (1 ton/year) and Saccorhiza polyschides (500 kg/year), in addition to other species in smaller quantities.

Under the premises of minimum processing of the product to avoid the loss of its properties, and the production of a lower impact on the environment, new agricultural inputs have been developed from these by-products that contain great benefits for plants and soil.

Initially, we worked on the production of algae extracts at laboratory and pilot scale to be applied to each crop, also performing induced growth tests, so that the range of activity and toxicity of the extracts could be known, as well as tests to find the optimal doses.

After performing the corresponding quality control analyses on the stored algae, and based on the average values of nutrients, metals and microbiological values obtained, the algae prepared in their different formats (as fertilizer in the field, as a component of growing media and as a biostimulant) were tested in potato, lettuce and grapevine fields. The formulations and calculation of the doses were made according to the nutritional needs of each crop, also taking into account the results of soil analysis and the nutritional characteristics of the algae.

The results of the use of algae, either as a substrate component or as a fertilizer, are promising. Its capacity to increase the aeration of the substrate as the algae dose increases is especially noteworthy, which is very useful for aerating substrates that tend to waterlogging.

The effects of dehydrated seaweed as a fertilizer have shown similar or better impacts than traditional cattle manure on lettuce and potato crops.

Likewise, the trials with biostimulants are giving significantly positive and very promising results in the project’s target crops, such as the 74% increase in commercial potato production with respect to the control sample or the 48% increase in lettuce weight with respect to control plots.

The following photographs show the different aspect of the planting of the Agria potato variety in a plot of one of the entities participating in this project. On the one hand, the image on the left shows the appearance of the aerial part of the potato crop in which no treatment has been applied (control plot); The image on the right shows the potato crop to which one of the algae extracts tested as a biostimulant (B2) has been applied.

Left: Without biostimulant / Right: With biostimulant B2 (6mL/L)

In the vine trials, no significant differences were observed between the control and the plants with algae fertilizer, but significant differences were observed when the biostimulants were applied, both in pots and in the field. A positive effect was observed, increasing shoot length and leaf size.

One of the most promising results of the project is the potential of the algae extract as a protective and/or preventive agent against fungal diseases of grapevine, since a lower incidence of downy mildew is observed with biostimulants, especially if they are applied before the fungal inoculum.

According to this, and based on the results obtained in the tests carried out during the execution of the ALGATERRA project, it can be determined that the application of active ingredients from marine algae to the different crops with which we have worked has positive effects on plants at very low concentrations.

Consequently, it can be concluded that ALGATERRA is presented as a viable alternative to respond to the demand of farmers in organic farming systems, making the activity around the Galician seaweed industry more environmentally, socially and economically sustainable, within the framework of a green and circular economy.

In addition to our headquarters and the company PORTO-MUIÑOS, S.L., the University of Santiago de Compostela through the Agronomy and Animal Science Research Group, the Biological Mission of Galicia, Horta da Lousa, Riveiro Ecológicos and Adegas Terra de Asorei have also participated in the execution of the ALGATERRA project.

The project is funded by the call for grants for the support of pilot projects, development of new products, practices, processes and technologies in the agroforestry field, co-financed with the European Agricultural Fund for Rural Development (EAFRD), under the Rural Development Program (RDP) of Galicia 2014-2020. The Consellería do Medio Rural is the body of the Galician Administration responsible for proposing and executing the general guidelines in the rural area and is responsible for agriculture, livestock, rural development and regional planning, rural structures, agri-food and forestry industries, forestry and forest fire prevention and defense.