2.4 Separation of different aggregation fractions
Soil samples were air-dried for separating different aggregation
fractions using a nest of 4 sieves having diameters of 2000, 250, and 53μ m (Zhang et al., 2012b). In brief, about 250g dry soil samples
were placed on the uppermost of the nest and had plane-rotary shaken
mechanically for 20min. The microsieve size (<250 μ m)
was further sieved by hand. Mechanism sieving was done 3 times. Finally,
three aggregation fractions were got, which were small macroaggregates
part (250-2000 μ m, CPOC), macroaggregates fractions (53-250μ m, FPOC), and silt and clay-sized particles (<53μ m, MOC). Particles larger than 2000 μ m were not got in
the present work. Weight and SOC contents of every aggregation fraction
were determined for calculating proportions of carbon storage.