Anne-Kristin Løes and Joshua Cabell: Closing land-to-sea nutrient gaps by new fertilisers

Significant efforts have been conducted over decades to reduce the loads of nitrogen (N) and phosphorus (P) to the Baltic Sea. Still, eutrophication remains a serious threat to water quality and biodiversity in this important inland ocean, and agricultural activities are the main sources of diffuse nutrient losses via drainage, runoff and erosion. Organic agriculture is acknowledged as one possible solution to reduce such nutrient flows, due to lower surpluses in farm and field level nutrient budgets compared with conventional farming. In most countries around the Baltic Sea, public support for organic production and consumption is well-established and strong. This has contributed to the unique position of Denmark, Estonia, Sweden, and Finland as leading countries in Europe when it comes to the proportions of organic consumption, farmland managed organically, and certified area for wild collection. Refraining from the use of mineral N fertilisers, organic farming systems rely on biological N fixation, and careful utilization of animal manures and other byproducts, often animal-derived. This has prompted a high interest in the development of bio-based fertilisers, to recycle nutrients and organic matter from societal waste. For example, struvite, a phosphate salt, may be precipitated from sewage, and is permitted for use in organic growing. This implies a recycling of valuable nutrients from fork to field and is a promising alternative to triple super phosphate in mineral fertilisers, which is made by acidification of rock phosphate. In general, the productivity per unit of farmland is lower in organic systems, and many stakeholders argue that only high-yielding industrialized agriculture can feed the world. Others have evaluated the food system across the Nordic countries and found that we can feed ourselves in a system with 100% organic agriculture, if our diet is changed to consume mostly vegetable and grain-based food.

In Norway, the Baltic Sea is not dominating the environmental discourse. However, with higher temperatures and stronger rainfall events, eutrophication is a serious challenge in lakes and fjords especially in the eastern and south-west parts of the country. Another relevant difference is the seafood industry, which is much larger than the agricultural sector in Norway. This is the opposite of the situation in other Nordic and in the Baltic countries. The Norwegian seafood industry has a much larger environmental footprint than the agricultural sector, not least because the aquaculture industry has grown extremely fast over the last 20 years, whereas agriculture has stagnated. The economic value of captured wild fish is roughly comparable to the value of raised fish. Cod and halibut are emerging raised species in addition to salmon. The decreasing quota of captured fish is a driver towards better utilization of left-over materials which are rich in both N and P such as fish bones. These are currently poorly utilized but have a high potential as a fertiliser with readily available nutrients for crop plants. The aquaculture industry imports high amounts of materials for fish feed, especially soybean meals. Significant proportions of the nutrients in fish feed are lost to the sea via excretion and feed loss. Whereas this does not directly affect the Baltic Sea, it is not a sustainable way to handle a valuable, scarce resource (P), or to handle reactive N. Efforts are made to reduce feed loss, and collect the sludge, composed of feces and feed loss, from closed systems. Cultivating seaweed to extract nutrients from the sea may be one option to mitigate the nutrient losses, which can also be of interest in the Baltic Sea. Cultivation and harvesting of wild seaweed have attained a large interest in recent years for various applications, not least for production of biostimulants to cope with drought. Brown macroalgae are most relevant for high production of biomass in a Nordic-Baltic context. Some species of brown macroalgae have high concentrations of valuable minerals relevant for complete fertilisers, such as potassium, magnesium, and sulfur.  Hence, they complement the fish residues, which are rich in N and P. Marine-derived materials are of high interest as a resource for making fertilisers and to close the nutrient gaps from land to sea, but there are challenges linked to the development of competitive value chains, the salinity of marine materials,  and the contents of potentially toxic elements such as cadmium and arsenic (seaweed), zinc (fish sludge), and persistent organic pollutants which tend to accumulate in the sea and in marine organisms.

Whereas Norway could learn a lot from the Baltic region to support the organic sector, which is very small in this country, the Baltic region could possibly learn from the Norwegian efforts to develop sustainable fertiliser products from marine-derived materials.