Document: ERL-3-59-43

Long-term changes in nitrogen loading across Chinese village landscapes.

ELLIS, E.C.*

University of California, Santa Cruz, CA 95064 ¹

Abstract:
China's N mobilization will comprise 25% of the world total by 2020, with 80% of this mobilization caused by N fertilizer use. The long-term impacts of increased N fertilizer use were measured by comparing N loading in 1930 versus 1994 across an entire agricultural village landscape in China's Tai Lake Region. Contemporary data were gathered on site from 1993-1996 using household surveys, fertilizer analysis and other field methods, while 1930s data were obtained from elder interviews, farm surveys, and other historical sources. N loading was greatest in rice/wheat paddy ecotopes, with synthetic N increasing from 0% in 1930 to >80% of fertilizer N in 1994. 1994 annual paddy N inputs averaged 480 kg N ha^-1 yr^-1 and varied between 210 and 850 kg N ha^-1yr^-1 in a sample of 50 households. As N inputs >500 kg N ha^-1 yr^-1 do not increase yields, 48% of village households exacerbated N losses with no yield benefit. These losses could be reduced significantly if only those households with above average N inputs lowered them to the average. Synthetic N also shifted human manure inputs from paddy fields, their most common destination in 1930, to the much smaller area of upland crops, with rates often >200 kg N ha^-1 yr^-1 in 1994, providing a likely source of nitrate leaching. The causes and consequences of enhanced N mobilization in China are best measured by integrating household and landscape data.

Keywords: biogeochemistry, nitrogen loading, agroecosystems, traditional agriculture, landscape ecology, long-term change

This abstract is being presented at: 3:30 PM in session:
AGROECOLOGY