2015 年 19 巻 1 号 p. 97-104
The impact of land use for fertilizer production has been evaluated in terms of total material requirement (TMR) with a central focus on phosphorus fertilizers. Three different ammonium phosphates, calcium superphosphate, fused magnesium phosphate, magnesium multi-phosphate and high analysis compound fertilizer were selected as phosphorus fertilizers. For comparison, nitrogen fertilizers such as urea, nitrolime, ammonium sulfate and ammonium chloride, and potassic fertilizers such as potassium sulfate and potassium chloride were chosen as well. Two types of functional units were considered: one was 1 kilogram of the target fertilizer production and the other was 1 kilogram of phosphorus pentoxide (P2O5), nitrogen (N), and/or potassium oxide (K2O). The system boundaries were set from mining to fertilizer production, and all the direct and indirect inputs were considered, along with hidden flows such as tailings and waste rocks. The TMRs of the fertilizers ranged from 5 to 23 kg/kg. It was found that the phosphorus fertilizers, excluding calcium superphosphate and fused magnesium phosphate, showed higher TMR than nitrogen or potassic fertilizers. The annual TMR with respect to fertilizer usage in Japan, which is defined as the product of the estimated TMR and amount of each fertilizer used in Japan in 2012, indicated that phosphorus fertilizers occupy about 69% of the total TMR, with high analysis compound fertilizer and ammonium phosphate in the majority. The TMR and life-cycle carbon dioxide (LCCO2) were found to be different indicators. Case studies were examined in which improvements in phosphoric acid and sulfuric acid production were considered. Improvements in phosphoric acid production were found to be more effective at reducing the TMR of phosphorus fertilizers. Finally, the following equation was proposed for simple estimation of diverse phosphorus, nitrogen and potassium- based fertilizers: TMR = 2 + 0.34 [%P2O5] + 0.15 [%N] + 0.098 [%K2O]
