A multi-regional soil phosphorus balance for exploring secondary fertilizer potential: the case of Norway
Phosphate rock is a non-renewable source of phosphorus (P) in mineral fertilizer and many countries need to use P fertilizer more efficiently in food production. This study explored the theoretical fertilizer potential of the P-rich bioresources animal manure and sewage sludge to supply the required P fertilizer for crops. We used Norway as a case study and employed multi-regional substance flow analysis with averaged annual data for the period 2009-2011. In a status quo soil balance for agricultural soil, all counties had a positive balance with a national average of 8.5 (range between counties of 2.7-14.7) kg P ha−1. In addition, two fertilizer regimes (FR) were evaluated for the period; FR1 omitted mineral P fertilizer from the balance and assumed bioresource addition matched plant P offtake regardless of soil available P, while FR2 omitted fertilizer from the balance and adjusted bioresource inputs according to whether soil available P was above (adjusted downwards) or below (adjusted upwards) the optimum soil P level. FR1 and FR2 gave a national average P surplus of 1.2 (range −7.0 to 11.2) and 6.2 (range −2.5 to 19.0) kg P ha−1, respectively. The secondary P fertilizer potential of bioresources for meeting P requirements was found to be underestimated in the short term by not taking into account the actual plant-available soil P level. Our conclusion was that the P fertilizer values of manure and sludge have the theoretical potential to meet the P fertilizer requirements of all Norwegian crops assessed in both the short-term and long-term perspective.