Net anthropogenic phosphorus inputs (NAPI) index application in Mainland China.

This study provides a new understanding on sources of P, which may serve as a foundation for further exploration of anthropogenic effects on P input. Estimation of net anthropogenic phosphorus input (NAPI) was based on an inventory of phosphorus (P) fertilizer use, consumption of human food and animal feed, seeding phosphorus and non-food phosphorus net flux. Across Mainland China, NAPI had an upward trend from 1981 to 2009, which reflects development trend of the population and economic. NAPI for years 1981, 1990, 2000 and 2009 are 190 kg P km(-2)yr(-1) (1.8 kg P per person yr(-1)), 295 kg P km(-2) yr(-1) (2.5 kg P per person yr(-1)), 415 kg P km(-2) yr(-1) (3.1 kg P per person yr(-1)) and 465 kg P km(-2) yr(-1) (3.4 kg P per person yr(-1)), respectively. On a geographical basis, NAPI per unit area is lower in northwest Mainland China than in southeast Mainland China with the largest NAPI of 3101 kg P km(-2) yr(-1) in Shanghai, while NAPI per person is in reverse with the largest NAPI 7.7 kg P per person yr(-1) in Tibet. P input of fertilizer is the largest source of NAPI, accounting for 57.35-83.73% (109-390 kg P km(-2) yr(-1)) of the total NAPI, followed by non-food P and P in human food and animal feed. Year 2000 was a critical point where P changed almost from net input to output. Grain production rate per unit mass of fertilizer showed an obvious downward trend. The primary factor in relation to the change in NAPI is total population.