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This article in JEQ

  1. Vol. 22 No. 1, p. 133-140
     
    Received: Oct 15, 1991


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doi:10.2134/jeq1993.00472425002200010017x

Nitrogen Transfers in a Rapidly Eroding Agroecosystem:Loess Plateau, China

  1. Hugh Hamilton * and
  2. Shiu-hung Luk
  1. Department of Geography and Inst. for Environ. Studies, Univ. of Toronto, Toronto, ON Canada M5S 1A1.

Abstract

Abstract

A study was initiated to assess the influence of high erosion rates and sediment hyperconcentrations on patterns of N loss in China's Loess Plateau region. The study was conducted in a 12.6-ha subbasin where the upper slopes are terraced and cultivated, and the lower slopes are grazed by sheep. Seventeen rainstorms were monitored over 2 yr at a flume located in the ephemeral channel at the basin outlet. Runoff events were characterized by large sediment concentrations (mean 508 kg m−3), dilution of dissolved NO3 + NO2-N concentrations during periods of peak flow, and high sediment-associated Kjeldahl N concentrations near the end of events when larger-sized particles are deposited. Hyperconcentrated flow ensured that most entrained sediment and N was exported. Annual soil losses equaled 203.4 Mg ha−1 and 176.9 Mg ha−1 in 1987 and 1988. Total N losses equaled 76.4 kg ha−1 and 44.1 kg ha−1. In each year, one or two large events contributed the bulk of soil and N losses. About 98% of the N losses were sediment associated, with low-intensity events having the highest soluble proportion. A simple N mass balance shows that erosion losses of N are serious, and that most of the N removed from both cultivated and grazed areas is exported. Results indicate that N cycling in this semiarid area is strongly influenced not only by the amount of rainfall, but also by the timing and intensity of the storms.

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