Changes in nitrogen flow in food and feed supply during 1992–2007 in Japan

Abstract

We estimated nitrogen flow in food and feed supply in 1992, 1997, 2002, and 2007 in Japan, and compared it with previously reported nitrogen flow in 1982 and 1987. Total nitrogen in domestic and imported food and feed in Japan increased until 1992, after which it decreased. The domestic ratio (domestic−exported)/(domestic−exported+imported) of the food and feed supply in Japan decreased from 42％ in 1982 to 30％ in 1997, and it stabilized at 28％ 2002 onwards. The domestic ratio decreased from 54％ in 1982 to 37％ in 2007 of diet food supply, 32％ in 1982 to 21％ in 2007 of feed supply for livestock farming, and rapidly from 33％ in 1987 to 15％ in 2002 of food and feed supply for food processing. The nitrogen load to the environment increased to its peak until to 1992, after which it decreased; this occurred due to a decrease in chemical fertilizer application. However, food and feed wastage in the system did not decrease, resulting in only a slight decrease in nitrogen load to the environment. The ratio of nitrogen load absorbed into domestic crop production to total nitrogen amount in domestic−exported+imported food and feed+crop residues decreased from 35％ in 1982 to 28％ in 1997, and was stable until 2007. The ratio of nitrogen load in waste recycled to farmland to total nitrogen amount in recycled waste+chemical fertilizer input to farmland increased from 26％ in 1982 to 39％ in 1997–2002, and decreased to 35％ in 2007. The ratio of nitrogen load from farmland to the hydrosphere per total nitrogen load to the hydrosphere decreased from 30％ in 1982 to 25％ in 2007.