NITROGEN FRACTIONS AND TRANSFORMATIONS OF VADOSE ZONE SEDIMENTS UNDER INTENSIVE AGRICULTURE IN OREGON
作者:
R. Dick,
R. Christ,
J. Istok,
F. Iyamuremye,
期刊:
Soil Science
(OVID Available online 2000)
卷期:
Volume 165,
issue 6
页码: 505-515
ISSN:0038-075X
年代: 2000
出版商: OVID
关键词: Vadose zone;nitrogen fractions and immobilization;microbial activity
数据来源: OVID
摘要:
Nitrate contamination of groundwater aquifers from agricultural fertilization is of growing concern. It is generally assumed that little biological activity occurs in the vadose zone and that NO−3moves through this zone unimpeded. Various N fractions and the microbial activity in the surface and vadose zone sediments from three agricultural soils in eastern Oregon were examined. Nitrate levels in the vadose zone were as high as 60 mg N kg−1soil, and fractionation showed that approximately 30% of total N was in the form of acid-insoluble N, which could be a sink for NO−3that becomes immobilized. The vadose zone also contained high concentrations of amino acid-N and amino sugar-N, suggesting that a significant amount of subsoil N is of biological origin. Significant levels of microbial biomass C and CO2respiration were found in sediments derived from the vadose zone. A 14-day lab incubation study showed that vadose zone sediments could mineralize organic N without additional C and that NO−3may be subject to biological immobilization when a high rate of glucose C (3000 mg kg−1) is present.
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