Effect of Clay Mineralogy and Soil Organic Carbon in Aggregates under Straw Incorporation

Bin Xue,Muhammad Kamran,Shah Fahad,Li Huang,Jianwei Lu,Ruili Gao,Xiaokun Li

doi:10.3390/agronomy12020534

Bin Xue, Muhammad Kamran + Show 5 more

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https://doi.org/10.3390/agronomy12020534

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Abstract

The interaction between soil organic carbon (SOC) and clay minerals is a critical mechanism for retaining SOC and protecting soil fertility and long-term agricultural sustainability. The SOC composition and minerals speciation in clay fractions (<2 μm) within soil aggregates under straw removed (T) and straw incorporation (TS) conditions were analyzed by X-ray diffraction, Fourier transform infrared spectra and X-ray photoelectron spectroscopy. The TS treatment promoted enrichment of clay in aggregates. The TS increased the contents of SOC (27.0–86.6%), poorly crystalline Fe oxide (Feo), and activity of Fe oxides (Feo/Fed); whereas, it reduced the concentrations of free Fe oxide (Fed) in the clay fractions within aggregates. Straw incorporation promoted the accumulation of aromatic-C and carboxylic-C in the clay fraction within aggregates. The relative amount of hydroxy-interlayered vermiculite, aliphatic-C, and alcohol-C in the clay fractions within the macroaggregates was higher than that microaggregates, whereas the relative amounts of illite, kaolinite, Fe(III), and aromatic-C had a reverse tendency. The hydroxy-interlayered vermiculite in clay fractions showed positive correlation with the amounts of C–C(H) (r = 0.93) and C–O (r = 0.96 *, p < 0.05). The concentration of Feo and Feo/Fed ratio was positively correlated with the amounts of C=C and C(O)O content in clay within aggregates. Long-term straw incorporation induced transformation of clay minerals and Fe oxide, which was selectively stabilized straw-derived organic compounds in clay fractions within soil aggregates.

Highlights

Stabilization of soil organic carbon (SOC) plays a key role in agricultural soil fertility and mitigation of global warming [1,2,3]
We found that the variation of organic C content among aggregates was consistent for three replicate clay fractions
Fe oxide (Feo) and Feo/Fe oxide (Fed) ratio was positively correlated with the abundance of aromatic-C (C=C) and carboxylic-C (C(O)O) in clay within aggregates (Figure 10), suggesting that the higher contents of poorly crystalline Fe minerals and Fe mineral availability promoted the selective adsorption of aromatic-C and carboxylic-C compounds in clay

Summary

Introduction

Stabilization of soil organic carbon (SOC) plays a key role in agricultural soil fertility and mitigation of global warming [1,2,3]. Soil aggregates physically protect SOC against mineralization, which decreases the availability of organic compounds for microorganisms, extracellular enzymes, and oxidation processes [4,5]. Stabilization of SOC results from the formation of organo–mineral associations, especially the adsorption of SOC by clay mineral aggregates and chemical reactions between SOC and surfaces of clay particles [6,7,8]. More than 70% of the SOC inventory exists in close association with minerals, which can protect organic carbon from microbial degradation in agricultural soils [12,13,14,15,16]

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