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Spatial variations of aggregate-associated humic substance in heavy-textured soils along a climatic gradient

Yujie Wei,Xinliang Wu,Rubing Zeng,C. Cai,Zhonglu Guo

Published 2020 in Soil & Tillage Research

ABSTRACT

Humic substances (HS), as important soil components, are crucial to soil fertility and ecology. The composition of HS is interlinked within the formation of aggregates, and jointly influences soil biogeochemical processes. However, little detailed and quantitative information is available on the association of the HS composition with aggregate distribution for soils spanning a broad range of climatic gradients (e.g., temperature and precipitation). Herein, the spatial distribution of HS and its chemical composition (humic acids, HAs; fulvic acids, FAs; iron-linked humin, HMi; clay-combined humin, HMc; and insoluble humin residue, HMr) associating with different sizes of aggregates (>0.25, 0.25∼0.05, and 0.25 mm) and higher concentration of HS was more significantly affected by climatic conditions than subsoil (F > 21, p  0.52, p < 0.01) and the proportion of its corresponding aggregate fraction (p < 0.05). Moreover, aggregate-associated fulvic acids were positively correlated with sesquioxides, clay content, 14 nm intergrade mineral and kaolinite, but negatively correlated with soil pH, bulk density, silt content, and vermiculite (p < 0.05). However, these physicochemical properties had an opposite effect on the variation of humic acids in macro- and micro- aggregates, and made different contributions to humins up to the subdivided composition and the associated aggregate size fraction. These results would contribute to the prediction accuracy of HS storage across scales, especially when a wide size-range aggregation and various geochemical factors are considered.

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