Phosphorus

Phosphorus is an essential element for plants, animals and humans and is also a scarce resource as a raw material for fertilizer production. The flows of phosphorus to and from Swedish agriculture and food chain was investigated with a material flow analysis (MFA). The fertilizer value of recycled phosphorus in chemically precipitated sewage sludge, biological sludge, mineral fertilizer and ash was investigated in a three-year field experiment. The impact of different phosphorus fertilizers on arbuscular mycorrhiza (AM) was studied in field and pot experiments, and the environmental impact of different phosphorus fertilizers was evaluated by Life Cycle Assessment (LCA). The results showed that Sweden has a positive phosphorus balance, but that phosphorus is concentrated on farms with more than one animal unit per hectare. Furthermore, the calculations were made on recent production and if Sweden increases the level of self-sufficiency, more phosphorus would be needed in the system. In a long-term perspective, the form of phosphorus fertilizer used seems to be less important than maintaining soil phosphorus content to ensure phosphorus delivery to the crop when conditions in terms of moisture, temperature etc. are optimal. Easily soluble phosphorus in mineral fertilizer can be essential in a short-term perspective under dry conditions, or on phosphorus-deficient soils. This thesis shows that with balanced phosphorus fertilization, it is possible to achieve good yield without compromising the possibilities for AM fungi to colonize roots. Phosphorus recovery from ash is costly in terms of both energy and carbon dioxide emissions. The most efficient option for sewage sludge is to use it directly on farmland, but associated cadmium addition to soils can be a problem. The cadmium imports with food and feed to Sweden are currently unknown. Nitrogen is a valuable nutrient and is energy-demanding to replace, so fertilization systems that can keep nitrogen in usable form for production are preferable. It was concluded that the energy and carbon dioxide bound during photosynthesis should be assigned to agricultural production and not the product user, e.g. a sludge incineration facility. Production of bioenergy should include all products that contain energy bound by photosynthesis, not only products used for fuel and heating