Abstract

Purpose

The chemistry of soil organic matter (SOM) is fundamental for sustainable and climate-smart agroecosystems. However, the differences in SOM chemistry between the upland and paddy soils developing under the same climatic and edaphic conditions are unclear.

Materials and methods

Py-GC/MS was applied to characterize the biochemical features of SOM in three physical size fractions: coarse particulate (> 0.25 mm, cPOM), fine particulate (0.053–0.25 mm, fPOM), and mineral-associated OM (< 0.053 mm, MAOM) of upland and paddy fields under long-term (> 30 years) mineral and manure fertilizations.

Results and discussion

Paddy fields had higher contents of soil organic carbon (SOC) and total nitrogen (TN) mainly accumulated in MAOM fraction than uplands. These two soils had different molecular compositions of SOM: N-containing compounds including amino-N and heterocyclic-N compounds enriched in the uplands, whereas paddy had higher proportions of lipids and phenolics. The SOM composition was also dependent on particle size, especially in the uplands, where POM fractions had high contents of lignin and MAOM accumulated N-containing components. In contrast, POM in paddy accumulated polysaccharides, whereas MAOM was enriched with lipids. Particle size controlled the C oxidation state (C_ox), and paddy soils had higher C_ox than that of uplands, mainly in the MAOM fraction.

Conclusions

The molecular composition SOM was primarily regulated by land-use type, following by fraction size and fertilization regime, while the C_ox was controlled by fraction size. The C_ox needs more attention to understand the direction of formation of SOM fractions.

中文翻译：

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旱田和水田土壤有机质生化组成及氧化态差异

摘要

目的

土壤有机质 (SOM) 的化学性质是可持续和气候智能型农业生态系统的基础。然而，在相同气候和土壤条件下发育的旱地土壤和水稻土之间的有机质化学差异尚不清楚。

材料和方法

Py-GC/MS 用于表征 SOM 的三个物理尺寸部分的生化特征：粗颗粒（> 0.25 mm，cPOM）、细颗粒（0.053–0.25 mm，fPOM）和矿物相关 OM（< 0.053 mm） ，MAOM）长期（> 30年）矿物和粪肥施肥下的旱地和稻田。

结果与讨论

稻田土壤有机碳（SOC）和全氮（TN）含量高于旱地，主要以MAOM组分积累。这两种土壤的SOM分子组成不同：高地富含氨基氮和杂环氮化合物等含氮化合物，而水稻则含有较高比例的脂质和酚类物质。 SOM 组成还取决于颗粒尺寸，特别是在高地，POM 部分具有高含量的木质素和 MAOM 积累的含氮成分。相比之下，稻谷中的 POM 积累了多糖，而 MAOM 则富含脂质。粒径控制了C氧化态（C _ox），水稻土的C _ox高于旱地，主要是MAOM​​部分。

结论

SOM 的分子组成主要受土地利用类型的调节，其次是组分大小和施肥方式，而 Cox 则_受组分大小控制。 C _x需要更多的关注来了解 SOM 组分的形成方向。