Due to the complexity of soil types and the environment, there is no universal theory
for the formation of aggregates. In the aggregate formation process, currently，organic
carbon effect has been extensively researched, and the research of inorganic colloids still in
a qualitative description, agglomeration process and the role of organic carbon and calcium
carbonate is mainly to whole soil or large aggregates, however, the distribution and
function of organic carbon and calcium carbonate in the particle size of aggregate remains
unclear. This study measured the distribution characteristics of soil organic carbon and
calcium carbonate in soil aggregates under typical vegetation communities in Ziwuling
forest area different depth soil profiles, and aggregate size distribution, stability
characteristics, pore textural characteristics drivened by the two cementing material, reveal
soil aggregate formation and stability mechanism under different bonding cementing
characteristics. On the basis of the existing research, make the cementation on soil
aggregate formation and stable process further clear, and provide theoretical support and
decision-making basis for soil carbon sequestration, soil and water conservation. The main
results are as follows:
1. The distribution of organic carbon in soil profiles
Soil organic carbon content were with profile gradually reduce, 0-10cm soil organic
carbon content was higher than 15g.kg -1 and 10-20cm soil organic carbon content is about
10g.kg -1 and below 20cm soil organic carbon content is less than or equal to 5g.kg -1 ;
organic carbon mainly in 0-20cm soil aggregates play mainly cementation.
The organic carbon content of the grain size aggregates decreased with the profile of
the organic carbon content. The organic carbon fraction of >5 mm and 0.053-0.25mm
fractions increased with the depth of the profile, and the organic carbon contribution rate of
other grain fractions decreased gradually with the increase of the profile. The contribution
of organic carbon in microaggregates was the highest, and the organic carbon contribution
rate of the aggregates decreased with the decrease of the particle size.
2. The distribution of organic carbon fractions of soil profiles The contents of organic carbon fractions decreased gradually along with the
deepening of the profile. The organic carbon of the 0-10cm soil layer is the main
constituent, and the organic carbon of the 10-100cm layer is the main part of the organic
carbon. Along with the depth of the profile, the proportion of particulate organic carbon
decreases, and the stability of the mineral bound organic carbon increases.
The contents of organic carbon fractions of the fractions decreased with the deepening
of the profiles, and decreased with the deepening of the profile. The same soil layer
decreased with the increase of the size of the organic carbon, but the difference was mainly
reflected in the large aggregates and micro aggregates. The organic carbon contribution
rate of the microaggregates were the highest, and the organic carbon contribution rate of
large aggregates fractions decreased with the particle size smaller.
3. Distribution of calcium carbonate in soil profiles
The content of calcium carbonate in the 0-70cm soil layer increased with the depth of
the profile, and reached the maximum in the 40-70cm soil layer, is 100.65g.kg -1 . Then
decreased slightly in the 70-100cm soil layers. Calcium carbonate is the main cementing
substance in the 40-100cm soil layer.
The changes of the contents of calcium carbonate in the same soil layer were not
significant. The contribution of calcium carbonate in the soil profile, >5mm and
0.053-0.25mm fractions increased with the depth of the profile, and others’ decreased with
the depth of the profile. The calcium carbonate contribution rate of the microaggregates
were the highest, and the calcium carbonate contribution rate of large aggregates fractions
decreased with the particle size smaller.
4. The stability of soil aggregates in different soil cement materials
In the same soil layer, the ratio of micro aggregates is the largest, and the stability is
near 27%. The size of large aggregates decreases with the size of the particles. The organic
carbon plays an important role in soil agglomeration in 0-20cm soil layer, and the calcium
carbonate plays a major role in the soil agglomeration in 20-100cm soil layer. Kinds
of >0.25 mm soil water stable aggregates with depth and gradually reduce, failure rate with
soil depth increases gradually, this difference is mainly reflected in the 0-20cm, 20-40cm,
40-100cm three layers. The stability of aggregates decreases with the deepening of the
profile. The stability of aggregate was determined by the stability of >1mm particles.
Organic carbon and its components is significantly negative correlated with the
particle size of aggregate rate of destruction, the stability of aggregate was determined by
them and mainly reflected in the >1mm aggregates. The effect of calcium carbonate on the stability of the aggregates was significantly weaker than that of organic carbon and its
components, and it was mainly reflected in the conversion of organic carbon indirectly.
5. The pore structure of soil aggregates in different soil cement materials
The total porosity of soil decreased gradually with the deepening of the profile.
Aggregate porosity with increasing soil depth increases, but soil pore distribution indicated:
0-40cm soil aggregate pore structure is 40-100cm has more capillary porosity and aeration
porosity and has better permeability and protect the function of water and fertilizer.
Different size aggregate porosity size and distribution is different, each size class
reunion total pore volume and porosity in order as follows: 2-5mm>>5mm>1-2mm. The
content of 5-2mm aggregate was the largest, and the total porosity and porosity also were
the largest. The porosity of 1-2mm aggregates was the largest, and the aeration porosity of
was the largest in >5mm aggregates, and was 12.67%.
Organic carbon content and reunion total pore number, aggregate porosity show
negative correlation, and aeration porosity showed positive correlation; calcium carbonate
content and total pore quantity, aggregate porosity presented positive correlation. The
increase of organic carbon is mainly to improve the pore structure of aggregates, and
increase the effective porosity of aggregates, while the carbonate is mainly to increase the
porosity of aggregates.
Key words: organic carbon and composition, calcium carbonate, aggregate, stability,