秸秆深还对土壤团聚体中胡敏酸结构特征的影响

EFFECT OF DEEP APPLICATION OF STRAW ON COMPOSITION OF HUMIC ACID IN SOIL AGGREGATES

秸秆深还（Deep application of straw, DAS）是指将玉米秸秆施入土壤亚表层（20～40cm），可以解决秸秆焚烧的问题，同时提高土壤肥力、蓄水能力和作物产量。本文采集了吉林农业大学试验站玉米连作耕地试验田中的秸秆深还土壤和未秸秆深还土壤，采用湿筛法将其分为〉2mm、2～0．25mm、0．25～0．053mm和〈0．053mm 4个粒级，定性分析提取胡敏酸（HA），通过元素组成、红外光谱和差热分析研究了秸秆深还对黑土各粒级团聚体中HA结构特征的影响。结果表明：黑土团聚体中的优势粒级为2—0．25mm粒级，优势粒级的团聚体含量和有机碳含量均是表层较亚表层低，DAS有利于优势粒级团聚体的形成，促使优势粒级团聚体中有机碳增多；与亚表层相比，表层各粒级团聚体HA的缩合度、氧化度和热稳定性普遍较低，脂族碳／羧基碳和脂族碳／芳香碳较高；DAS促使土壤表层和亚表层各粒级团聚体中HA的缩合度、氧化度和热稳定性下降，其中表层HA的缩合度降低更明显；而亚表层氧化度和热稳定性的降低幅度较大。表层中HA的分子结构较亚表层的简单、年轻，秸秆深还促使土壤中有机碳含量增加，HA的结构简单化、年轻化。

Deep application of straw （ DAS ） refers to a technique of incorporating crushed corn stalk into the subsoil layer （20- 40 cm ） . It may effectively improve straw utilization rate, reduce straw burning rate, extend the extent of soil building from previously topsoil down to subsoil, contribute to accumulation of organic matter in the subsoil layer, help solve problems like thinning of the plow layer, shallowing, thickening and hardening of the plow pen, and lacking organic matter, and achieve the ends of higher soil fertility, higher water holding capacity, and higher crop yield. There used to be quite a number of researches focused on effect of DAS on soil physical properties, and few on soil chemical properties, let alone its effect on humus composition in soil aggregates. This paper mainly studies changes in structure of humic acid （ HA ） in soil aggregates in the topsoil and subsoil layers caused by DAS, so as to provide some theoretical basis for solutions to how to improve soil fertility and build up a proper plow layer. Soil samples were collected from an experimental mono-cropping corn field which had two plots, DAS and non DAS, in the Jilin Agricultural University. Four factions of soil aggregates, 〉2 mm, 2- 0.25 ram, 0.25- 0.053 mm and〈0.053 mm were screened out of the samples separately, with the wet sieve method and HA extracted for analysis of element composition with infrared spectroscopy and differential thermal analysis. Comparison was performed to determine effects of DAS on HA composition. Results show that the black soil tested was dominated with the fraction of 2 - 0.25 mm soil aggregates; however, the content of the dominant fraction and the content of organic carbon in the topsoil was lower than their respective ones in the subsoil; DAS was conducive to formulation of soil aggregates of the dominant fraction and increased the organic carbon content in the soil aggregates. Compared with that in the subsoil, the HA in soil aggregates, regardless of fractions, in the topsoil was lower in condensation degree and oxidation degree and thermal stability, and higher in aliphatic-C/carboxylic-C （ 2 920/1 720 ） and aliphatic-C/aromatic-C （ 2 920/1 620 ） ratios. DAS was found to reduce condensation degree, oxidation degree and thermal stability of HA in all soil aggregates in the topsoil and subsoil layers, especially HA condensation degree in the topsoil. On the other hand, oxidation degree and thermal stability of the subsoil layer also decreased obviously. The HA in the topsoil was simpler in structure and younger than that in the subsoil layer. So, DAS may also promote accumulation of organic carbon in the soil and make HA simpler and younger in structure.