7U.S.Environmental Protection Agency 1994.Nationalwater quality inventory A.1992 Report to Congress.U.S.EPA 841 R 001 C.Office of Water.U.S.Govt.PrintingOffice,Washington D.C.USA:
8John M.Antle,Donald C.Cole,Charles C.Crissman.Further Evidence on Pesticides,Productivity and Farmer Health:Potato Production in Ecuador.Agriculture ecnomics,1998,18:199-207
5Trenkel M E. Improving fertilizer use efficiency controlled-release and stabilized fertilizers in agricuhure[M].Paris:International Fertilizer Industry Association,1997:61 - 64.
6U S Environmental ProtectionAgency 1994.Nationalwater quality inventoryA.1992 Report to Congress U S EPA 841 R 001 C. Office of Water.U S Govt.PrintingOffice, WashingtonD.C.USA: PublishedM arch 1994.
7Earl O Heady, John L Dillon. Agricultural Production Functions. USA:Iowa State Univeresity Press, 1961.
8WinpennyJ T. Valuesfor the Environment. London:Hmso Publishing Centre, 1991:59 - 60.
10HUANG J,ROZELLE S.Technological change:Rediscovering the engine of productivity growth in China’s agricultural economy[J].Journal of development economics,1996,49(2):337-369.