title: [Humus composition and stable carbon isotope natural abundance in paddy soil under long-term fertilization].
abstract: Soil samples were collected from an experimental paddy field with long-term (26 years) fertilization in Taihu Lake region of Jiangsu Province to study the effects of different fertilization on the organic carbon distribution and stable carbon isotope natural abundance (delta 13C) in the soil profile, and on the humus composition. The results showed that long-term fertilization increased the organic carbon content in top soil significantly, and there was a significantly negative exponential correlation between soil organic carbon content and soil depth (P < 0.01). The organic carbon content in 10-30 cm soil layer under chemical fertilizations and in 20-40 cm soil layer under organic fertilizations was relatively stable. Soil delta 13C increased gradually with soil depth, its variation range being from -24% per thousand to -28 per thousand, and had a significantly negative linear correlation with soil organic carbon content (P < 0.05). In 0-20 cm soil layer, the delta 13C in treatments organic manure (M), M + NP, M + NPK, M + straw (R) + N, and R + N decreased significantly; while in 30-50 cm soil layer, the delta 13C in all organic fertilization treatments except R + N increased significantly. Tightly combined humus (humin) was the main humus composition in the soil, occupying 50% or more, and the rest were loosely and stably combined humus. Long-term fertilization increased the content of loosely combined humus and the ratio of humic acid (HA) to fulvic acid (FA).
authors.affiliation: Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China. lma@mail.issas.ac.cn
authors.forename: Li
authors.initials: L
authors.lastname: Ma
authors.forename: Lin-Zhang
authors.initials: LZ
authors.lastname: Yang
authors.forename: En
authors.initials: E
authors.lastname: Ci
authors.forename: Yan
authors.initials: Y
authors.lastname: Wang
authors.forename: Shi-Xue
authors.initials: SX
authors.lastname: Yin
authors.forename: Ming-Xing
authors.initials: MX
authors.lastname: Shen
mesh_terms: D002244:Carbon / Q000032:analysis; D002247:Carbon Isotopes; D005308:Fertilizers; D006812:Humic Substances / Q000032:analysis*; D012275:Oryza / Q000254:growth & development*; D012987:Soil / Q000032:analysis*; D013997:Time Factors
chemical_list: D002247:Carbon Isotopes; D005308:Fertilizers; D006812:Humic Substances; D012987:Soil; D002244:Carbon