Organic recycled fertilizer products optimized for forest fertilization

Currently, only about 50,000 hectares of Finnish forests are fertilized annually, which is a relatively small proportion of the total forest area, which is about 20 million hectares. The need for fertilization is, however, clearly greater, but it is limited by the fact that the returns will only come years later. Forests therefore have significant potential for expanding nutrient recycling and growing the fertilizer market. Currently, fertilizer products used in forests may not contain ingredients that are still waste as referred to in Section 5 of the Waste Act (646/2011), with the exception of ash in component material category 8. In practice, this means that only CE-marked organic fertilizer products in accordance with the EU Fertilizer Regulation (https://eur-lex.europa.eu/legal-content/FI/TXT/?uri=CELEX%3A02019R1009-20220716 ) can be used. If the amendment proposal to the Fertilizing Product Decree, which was subject to statements in the end of 2024, is implemented, fertilizers in accordance with the Fertilizer Act (711/2022) would also be permitted in forest fertilizer products, which consist exclusively of component materials marked as suitable for forest fertilization in the catalogue of component materials. In practice, this would allow the use of a fertilizer product containing a waste component in forests if the Finnish Food Authority permitted the use of that component material in the catalogue of component materials. However, this requires that the use of the component material in forest fertilizers can be demonstrated to be safe. Allowing the waste component in forest fertilizer products opens up the possibility of significantly increasing nutrient recycling in forest fertilization. This potentially promotes nutrient recycling, as the forest fertilization season lasts throughout the period soil is unfrozen, while in agriculture it is practically limited to the beginning of the growing season.

This project is funded by the Ministry of the Environment's AHTI program (https://ym.fi/vesien-ja-meren-tilan-parantaminen), and it is one of the follow-up projects of the project 'Recycled organic fertilizing products for forests – busting the myths (RofBustMyth)' implemented with Luke's thematic funding. The project specifically studies the migration of sewage sludge-based organic fertilizer products, organic pollutants, drug retention and harmful metals and nutrients in the forest ecosystem with the aim of producing scientific research data as a basis for allowing their use in forests. It also aims to develop organic recycled fertilizer products optimized for forest use, the nutrient concentrations of which can be increased and nutrient ratios corrected with mineral nutrient components. The key raw materials of these fertilizer products are sewage sludge and animal manure. The behavior of fertilizer products and their nutrients and pollutants is studied in mast, container and soil monolith experiments utilizing Luke's research platforms, e.g. Joensuu Root Laboratory. The project can establish new field trials that will be utilized in future projects, as this funding instrument does not allow for long-term monitoring. However, the project will utilize field trials established by Luke and other actors, especially in the catchment area of the Archipelago Sea, in accordance with the priorities of the funding instrument. In addition to environmental impacts, the achieved growth responses can be determined from previously established trials. Slow-soluble nutrients in organic fertilizer products are potentially better suited for forest use than for field use, because fertilization is carried out at intervals of several years. Allowing the forest use of fertilizer products containing a waste component would significantly promote nutrient recycling and reduce the nutrient load of the Archipelago Sea but also other water bodies, because their utilization of nitrogen and phosphorus would potentially improve significantly. Based on the results of previous studies, slow-soluble nutrients produce a better growth response in forest use than in agricultural production. Directing recycled nutrients to forestry use instead of agricultural use would potentially reduce environmental pollution and the economic benefits derived from them.