We conducted a pot experiment to study the fertilization effects of four N- and P-rich organic waste resources alone and in combination with K-rich bottom wood ash at two application rates (150 kg N ha–1 + 120 kg K ha–1, 300 kg N ha-1 + 240 kg K ha–1). Plant-available N was the growth-limiting factor. 48–73% of N applied with meat and bone meal (MBM) and composted fish sludge (CFS) was taken up in aboveground biomass, resulting in mineral fertilizer equivalents (MFE%) of 53–81% for N uptake and 61–104% for yield. MFE% of MBM and CFS decreased for increasing application rates. Two industrial composts had weak N fertilization effects and are to be considered soil conditioners rather than fertilizers. Possible P and K fertilization effects of waste resources were masked by the soil’s ability to supply plant-available P and K, but effects on plant-available P and K contents in soil suggest that the waste resources may have positive effects under more nutrient-deficient conditions.

One of the bottlenecks to efficient phosphorus (P) recycling is limited understanding of the relationships between inorganic P species in waste products and their P fertilisation effects. In this study, we characterised inorganic P species in seven waste products (two biomass ashes, meat bone meal, fish sludge, catering waste and two food waste-based digestate products) and two manure products (dairy and chicken manure) by: (1) Sequential chemical fractionation, (2) X-ray powder diffraction and (3) solid-state 31 P MAS-NMR spectroscopy. We then used the characterisation data to explain the results of a bioassay studying the fertilisation effects of waste and manure products after application to a nutrientdeficient model soil that was limed to two pH levels (approximately pH 5.5 and 6.9 at pH level 1 and 2), with ryegrass (Lolium multiflorum) as the experimental crop. The P in waste products was mainly present as a complex mixture of inorganic P species, predominantly Ca phosphates with differing solubility. Fertilisation effects were largely explained by sequential fractionation data, with a positive relationship between apparent P use efficiency and the H 2 Osoluble inorganic P fraction at pH level 1 (R 2 = 0.52) and a negative relationship between apparent P use efficiency and the HCl-soluble inorganic P fraction at pH level 2 (R 2 = 0.66). X-ray powder diffraction and solid-state 31 P MAS-NMR spectroscopy confirmed the sequential fractionation data, but provided little additional information.

This study examined the P fertilization effects of 11 sewage sludges obtained from sewage treated with Al and/or Fe salts to remove P by a pot experiment with ryegrass (Lolium multiflorum) and a nutrient-deficient sand-peat mixture. Also it investigated whether fertilization effects could be predicted by chemical sludge characteristics and/or by P extraction. The mineral fertilizer equivalent (MFE) value varied significantly but was low for all sludges. MFE was best predicted by a negative correlation with ox-Al and ox-Fe in sludge, or by a positive correlation with P extracted with 2% citric acid. Ox-Al had a greater negative impact on MFE than ox-Fe, indicating that Fe salts are preferable as a coagulant when aiming to increase the plant availability of P in sludge. The results also indicate that sludge liming after chemical wastewater treatment with Al and/or Fe salts increases the P fertilization effect.

Summary Future phosphorus (P) scarcity and eutrophication risks demonstrate the need for systems‐wide P assessments. Despite the projected drastic increase in world‐wide fish production, P studies have yet to include the aquaculture and fisheries sectors, thus eliminating the possibility of assessing their relative importance and identifying opportunities for recycling. Using Norway as a case, this study presents the results of a current‐status integrated fisheries, aquaculture, and agriculture P flow analysis and identifies current sectoral linkages as well as potential cross‐sectoral synergies where P use can be optimized. A scenario was developed to shed light on how the projected 2050 fivefold Norwegian aquaculture growth will likely affect P demand and secondary P resources. The results indicate that, contrary to most other countries where agriculture dominates, in Norway, aquaculture and agriculture drive P consumption and losses at similar levels and secondary P recycling, both intra‐ and cross‐sectorally, is far from optimized. The scenario results suggest that the projected aquaculture growth will make the Norwegian aquaculture sector approximately 4 times as P intensive as compared to agriculture, in terms of both imported P and losses. This will create not only future environmental challenges, but also opportunities for cross‐sectoral P recycling that could help alleviate the mineral P demands of agriculture. Near‐term policy measures should focus on utilizing domestic fish scrap for animal husbandry and/or fish feed production. Long‐term efforts should focus on improving technology and environmental systems analysis methods to enable P recovery from aquaculture production and manure distribution in animal husbandry.