Organic amendments under crop rotation influence soil organic matter (SOM) content, while the distribution and structural changes of humic substances have not been thoroughly examined. Three‐dimensional excitation‐emission matrix (3DEEM) fluorescence spectroscopy with parallel factor analysis (PARAFAC) and fluorescence regional integration (FRI), and projection procedure regression (PPR) were used to comprehensively evaluate the structural characteristics and distribution of fulvic acids (FA). The fertilization regimes were: CNoF‐SNoF (corn and soybean without fertilizer), CCF‐SNoF (corn with chemical fertilizer and soybean without fertilizer), CCR‐SNoF (corn and soybean stovers with chemical fertilizer and soybean without fertilizer), CCF‐SCF (corn and soybean with chemical fertilizer), and CCF‐SFM (corn with chemical fertilizer and soybean with dairy manure). Six‐year organic amendments mainly increased SOM, FA and humic acids (HA) contents, and the ratio of HA to FA (HA/FA), the ratio of percent fluorescence response in the ultraviolet to visible region (P_V,n/P_III,n) and projection values in topsoil. Six‐year stover return enhanced labile fractions of SOM in 20–30 cm soil depth, while dairy manure application increased labile fractions of SOM in 0–10 cm and 20–30 cm soil depths. The organic amendments had higher Fmax of component C1 (bioavailable aliphatic compounds) and component C2 (high molecular structure compounds), which could potentially enhance the supply of nutrients while reducing the impact of agriculture on the environment. The increase of fulvic acid‐like substances in the visible region was a major cause of the increase in humification degree. EEM‐PARAFAC, EEM‐FRI, and PPR analyses were all suitable for evaluating humification degree of FA.

中文翻译：

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受六年有机修正影响的腐殖质及其在软体动物中的分布

作物轮作下的有机改良剂会影响土壤有机质（SOM）的含量，而腐殖质的分布和结构变化尚未得到彻底检查。三维激发-发射矩阵（3DEEM）荧光光谱结合并行因子分析（PARAFAC）和荧光区域积分（FRI），以及投影程序回归（PPR）用于全面评估黄腐酸（FA）的结构特征和分布。施肥方式为：CNoF-SNoF（玉米和大豆不使用化肥），CCF-SNoF（玉米和化肥和不使用化肥的玉米），CCR-SNoF（玉米和大豆化肥和不使用化肥的大豆秸秆），CCF-SCF （玉米和大豆以及化肥），和CCF-SFM（玉米和化肥，大豆和奶牛粪）。六年有机修正主要增加了SOM，FA和腐殖酸（HA）的含量，以及HA与FA的比率（HA / FA），紫外线与可见光区域的荧光响应百分比比率（P_V，n / P _III，n）和表土中的投影值。六年秸秆还田增加了20–30 cm土壤深度中SOM的不稳定部分，而施用乳肥增加了0–10 cm和20–30 cm土壤深度中SOM的不稳定部分。有机修饰物具有较高的组分C1（可生物利用的脂肪族化合物）和组分C2（高分子结构化合物）的Fmax，这有可能增加营养素的供应，同时减少农业对环境的影响。可见区中富里酸样物质的增加是腐殖化程度增加的主要原因。EEM-PARAFAC，EEM-FRI和PPR分析均适合评估FA的增湿程度。