长期施有机肥和化肥对潮土胡敏酸结构特征的影响

以河南封丘长期肥料试验为平台,选择有机肥(OM)、化肥NPK(NPK)和不施肥(CK)3种处理,研究了不同施肥措施对潮土胡敏酸(HA)结构特征的影响。HA样品经提取纯化后,采用一系列固态~(13)C核磁共振(NMR)技术并结合元素分析和稳定碳同位素(δ~(13)C)技术对其结构进行定量表征。其中NMR技术包括高速多重倾斜幅度交叉极化/魔角自旋(multiCP/MAS)、偶极相移、化学位移各向异性过滤和质子碳编辑技术。结果表明:长期施有机肥和NPK肥增加了HA的饱和程度、氧化程度和极性,但缩合程度降低;HA的δ~(13)C值降低,表明有新的有机碳进入HA中。潮土HA以脂肪族化合物为主,烷基比例最高,占全碳的24.1%~26.3%;δ64~44处同时存在含氮烷基和甲氧基,且含氮烷基比例更高;另外异头碳和烷氧基中的非质子碳比例均很低。HA的芳香族成分中,δ142~113芳香碳以质子碳为主,且有少量质子芳香碳存在于δ113~93。结果还表明施肥均降低了HA的羧基和δ142~113芳香碳比例,增加了烷氧基和甲氧基比例;施有机肥还增加了酚碳和含氮烷基比例,降低了烷基比例。本研究表明长期施用有机肥和NPK肥使潮土HA结构向着疏水性程度和分解程度降低的方向发展;OM和NPK处理均使糖类物质增加,OM处理还使木质素和多肽增加,脂类物质降低。不同施肥模式下HA的形成机制不同。

Effects of Long Term Application of Organic Manure and Chemical Fertilizer on Structure of Humic Acid in Fluvo-aquic Soil

[Objective]Fertilization has become increasingly common to increase soil organic matter (SOM)content and improve soil fertility. Research suggests that fertilization promotes production of humic acids(HAs),one of the most important component of SOM. However little is known about the quantitative effects of fertilization on structural characteristics of HAs. Based on the long-term field fertilization experiment in Fegnqiu of Henan,effects of application of organic manure(OM),chemical fertilizer(NPK)and nothing(CK)on structure of HAs in fluvo-aquic soil were assessed. [Method]Soil samples were collected from the surface soil layers of three treatment plots,i.e. OM,NPK and CK,of a long-term winter wheat (Triticumaestivum L.)-summer maize(Zea mays L.)rotation experiment in Fengqiu,China. HAs were exhaustively extracted from the soil samples with a combined 0.1 mol L-1 NaOH and 0.1 mol L-1 Na4P2O7 solution and obtained through precipitation after acidification with 6 mol L-1 HCl. HF:HCl(1%:1%) solution was then used to purify the HAs obtained. In the end,the purified HAs were characterized with advanced solid-state 13C nuclear magnetic resonance(NMR)spectroscopy coupled with elemental analysis and isotopic analysis(δ13C). The NMR techniques included multiple cross-polarization/magic angle spinning (multiCP/MAS),dipolar-dephasing(DD),chemical-shift-anisotropy(CSA)filter and spectral editing of immobile CH2 and CH. [Result]Results show that long-term fertilization changed the element compositions,δ13C ratios and carbon functional groups of HAs,particularly significant in Treatment OM, and increased saturation degree,oxidation degree and polarity of HAs,but decreased condensation degree of HAs. The decrease of HAs in δ13C values indicated incorporation of new organic carbon into HAs. Advanced NMR techniques revealed that HAs in fluvo-aquic soil were composed predominantly of aliphatic compounds with alkyl being the highest in percentage(24.1%~26.3%). OCH3 and NCH signals both resonated aroundδ64~44,while the latter was prominent in proportion. Besides,the proportion of nonprotonated carbon was very low in anomeric and O-alkyl. Among the aromatics of HAs,they were dominated with protonated carbon in δ142~113,while only a little aromatic carbon existed in δ113~93,which cannot be detected with the routine cross-polarization/magic angle spinning(CP/MAS)NMR. It was also found that long-term fertilization reduced the percentages of COO/N-C=O and aromatic carbon of δ142~113,but increased the percentages of O-alkyl and OCH3. Moreover,application of organic manure also increased the proportions of aromatic C—O and NCH,but decreased that of alkyl.[Conclusion]In conclusion,all the findings in this study indicate that HA structure tends to be less hydrophobic with decreasing degree of decomposition. The application of either OM or NPK increases the content of carbohydrates in HAs. The application of OM also increases the contents of lignin and peptides,but decreases the content of lipids. The study also suggests that the advanced NMR techniques could provide great insight into HA structure and mechanisms of HA formation relative to fertilization pattern.