Original data-45-year long-term fertilization enhances soil organic carbon sequestration and soil aggregation
Description
Four fertilization treatments, based on a 45-year field experiment with winter-wheat and summer-maize rotation, were selected: CK (no fertilization); N (276 kg N kg ha–1); M (30,000 kg pig manure kg ha–1); MN (30,000 kg pig manure kg ha–1 + 276 kg N kg ha–1). Soil samples were collected from 0-5 cm, 5-10 cm, 10-20 cm and 20-30 cm soil layers based on soil-forming processes. The objectives were to: investigate the mechanisms underlying soil aggregate formation, stability, and SOC sequestration under long-term fertilization; explore the heterogeneous distribution and dynamic processes of soil functional groups across different treatments; clarify the microscale mechanisms of SOC sequestration under different fertilization regimes in non-calcareous Fluro-aquic soil. Soil organic carbon (SOC) and aggregate-associated SOC content was determined using the K2Cr2O7-H2SO4 digestion method. Soil bulk density (BD) was measured using a 100 cm3 ring knife. Undisturbed soil samples were used to measure water-stable aggregate fractions, and SOC stock and mean weight diameter (MWD) were calculated. Exchangeable K+, Na+, Ca²⁺ and Mg²⁺ were determined. Air-dried undisturbed soil samples were sieved through a 2 mm mesh and placed on filter paper. Ultrathin sections (200 nm thick) were cut using an ultramicrotome and transferred onto a carbon-free, 200-mesh silica-coated copper grid. SR-FTIR analysis was performed at the BL01B1 beamline, using a Thermo-Nicolet 6700 FTIR spectrometer coupled with a continuous-scan infrared microscope in reflection mode. Collected spectral data were processed. Subsequently, spectral curves representing the peak heights of Al-O (910 cm–1), Si-O-Si (1028 cm–1), aromatic C (1514 cm–1), and clay-OH (3621 cm–1) were generated. Spectra were extracted from each discrete point (5 μm interval) and 2D-COS analysis. Results showed that SOC content and stock decreased with increasing soil depth, particularly in the 20-30 cm layer. M and MN significantly increased SOC across all soil layers. Compared to CK, M and MN increased the proportion of soil macroaggregate (>0.25 mm) by 7.9%-18.4%, enhanced soil aggregate stability (MWD, increased by 53.3%-86.6%), and elevated intra-aggregate SOC contents. Partial least squares structural equation modeling (PLS-SEM) revealed the main driving pathways of SOC and MWD were “Fertilization-Ca2+ or Na+-MWD or Aggregates C-SOC” and “Fertilization-Ca2+ or Na+- Al-O or SOC or Clay-OH -MWD”. Synchrotron radiation-based Fourier transform infrared spectroscopy (SR-FTIR) combined with two-dimensional correlation spectroscopy (2D-COS) analysis demonstrated that organic amendment enhances SOC sequestration by promoting the formation of clay-OH, Si-O-Si, and Al-O functional groups. The relative peak area ratios of clay-OH, Si-O-Si, and Al-O in organic amendment treatments were 0.43-2.03 times higher than those in CK. In addition, soil functional groups exhibited high heterogeneity at microscale levels.
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Institutions
- Qingdao Agricultural University