Soil aggregate and its response to land management practices (original) (raw)

Soil aggregation dynamics and carbon sequestration

The quantity and quality of residues determine the formation and stabilization of aggregate structure for soil organic carbon (SOC) sequestration. Plant roots and residues are the primary organic skeleton to enmesh the inorganic particles together and build macro-and microaggregates while sequestering SOC. There are three major organic binding agents of aggregation: temporary (plant roots, fungal hyphae, and bacterial cells), transient (polysaccharides), and persistent (humic compounds and polymers). Conversion of natural ecosystems into agricultural lands for intensive cultivation severely depletes SOC pools. Magnitude of SOC sequestration in the soil system depends on the residence time of SOC in aggregates. Microaggregates are bound to old organic C, whereas macroaggregates contain younger organic material. Many techniques have been used to assess the SOC distribution in aggregates. Classical methods include SOC determination in aggregate fractions by wet and dry sieving of bulk soil. Isotopic methods including the determination of 13 C and 14 C with mass spectrometry are techniques to quantify the turnover and storage of organic materials in soil aggregates. Other techniques involve the use of computed tomography, X-ray scattering, and X-ray microscopy to examine the internal porosity and inter-aggregate attributes of macro-and microaggregates. Current state-of-knowledge has not unravelled completely the underlying complex processes involved in the sequestration, stability, dynamics, and residence times of SOC in macro-and microaggregates. There is a need to develop a unique conceptual model of aggregate hierarchy.

Effect of plant communities on aggregate composition and organic matter stabilisation in young soils

Objectives Carbon (C) content in pools of very young soils that developed during 45 years from loess was analysed in relation to vegetation: deciduous and coniferous forests and cropland. We hypothesised that variations in the amount of particulate organic matter (POM) can explain the C accumulation and also affects the C bound to mineral surfaces in soil under various vegetation. Methods Soil samples were collected under three vegetation types of a 45-year-old experiment focused on initialsoildevelopment.Aggregateanddensityfractionations were combined to analyse C accumulation in large and small macro- and microaggregates as well as in free and occluded POM and mineral factions. Results Deciduous forest soil accumulated the highest C contentinthe0–5cmlayer(43gCkg −1),whereasvalues in coniferous forest and arable soils were lower (30 and 12 g C kg−1, respectively). The highest portion of C in arable soil was accumulated in the mineral fraction (80 %), whereas 50–60 % of the C in forest soils were in POM. More C was associated with minerals in deciduous forest soil (16 g C kg−1 soil) than under coniferous forest and arable land (8–10 g C kg −1 soil). Conclusions Particulateorganic matterexplainsmostof the differences in organic C accumulation in soils developed during 45 years under the three vegetation types on identical parent material. The C content of the mineral soil fraction was controlled by plant cover and contributed the most to differences in C accumulation in soils developed under similar vegetation type (forest)