title: Organic nitrogen components in soils from southeast China.
abstract: OBJECTIVE
  To investigate the amounts of extractable organic nitrogen (EON), and the relationships between EON and total extractable nitrogen (TEN), especially the amino acids (AAs) adsorbed by soils, and a series of other hydrolyzed soil nitrogen indices in typical land use soil types from southeast China. Under traditional agricultural planting conditions, the functions of EON, especially AAs in the rhizosphere and in bulk soil zones were also investigated.
  
  
  METHODS
  Pot experiments were conducted using plants of pakchoi (Brassica chinensis L.) and rice (Oryza sativa L.). In the rhizosphere and bulk soil zone studies, organic nitrogen components were extracted with either distilled water, 0.5 mol/L K2SO4 or acid hydrolysis.
  
  
  RESULTS
  K2SO4-EON constituted more than 30% of TEN pools. K2SO4-extractable AAs accounted for 25% of EON pools and nearly 10% of TEN pools in rhizosphere soils. Overall, both K2SO4-EON and extractable AAs contents had positive correlations with TEN pools.
  
  
  CONCLUSIONS
  EON represented a major component of TEN pools in garden and paddy soils under traditional planting conditions. Although only a small proportion of the EON was present in the form of water-extractable and K2SO4-extractable AAs, the release of AAs from soil exchangeable sites might be an important source of organic nitrogen (N) for plant growth. Our findings suggest that the content of most organic forms of N was significantly greater in rhizosphere than in bulk soil zone samples. However, it was also apparent that the TEN pool content was lower in rhizosphere than in bulk soil samples without added N.
authors.affiliation: Ministry of Education Key Laboratory of Environmental Remediation and Ecosystem Health, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China.
authors.forename: Xian-you
authors.initials: XY
authors.lastname: Chen
authors.forename: Liang-huan
authors.initials: LH
authors.lastname: Wu
authors.forename: Xiao-chuang
authors.initials: XC
authors.lastname: Cao
authors.forename: Yuan-hong
authors.initials: YH
authors.lastname: Zhu
mesh_terms: D000596:Amino Acids / Q000032:analysis*; D002681:China; D009584:Nitrogen / Q000032:analysis*; D009930:Organic Chemicals / Q000032:analysis*; D027343:Rhizome / Q000737:chemistry*; D012987:Soil / Q000032:analysis* / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D009930:Organic Chemicals; D012987:Soil; D009584:Nitrogen
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