Aggregation influence conservation and mineralization of
soil C and N but aggregate separation method may influence levels of aggregate
amount and C and N pools. We compared aggregate amount and soil organic C
(SOC), soil total N (STN), particulate organic C and N (POC and PON), microbial
biomass C and N (MBC and MBN), potential C and N mineralization (PCM and PNM),
NH4-N, and NO3-N concentrations in aggregates separated
by dry and wet sieving methods. The PCM, PNM, MBC, and MBN are considered as
active pools, SOC and STN as slow pools, POC and PON as intermediate pools, and
NH4-N and NO3-N as available pools. Aggregate separation
was made in soil samples from 0 to 5 and 5 to 20 cm depths with various
properties and cropping systems in eastern Montana
and western North Dakota.
Aggregate amount was higher in dry than in wet sieving in 4.75- to 2.00-mm size
class but the amount varied between sieving methods in other size classes. In
cultivated soil, no definite trends in C pools were observed between aggregate
size classes and sieving methods. In no-till grassland soil, C pools were
higher in <0.25 mm than in 4.75-2.00 mm aggregates in dry sieving method but
the trend reversed in wet sieving method. Nitrogen pools in aggregates were
higher in <0.25 mm than in other size classes, regardless of sieving
methods. In all aggregates, active and available N pools were 2- to 30-fold higher in dry than in wet sieving method. Dry
sieving of moist soil can be a rapid and reliable method of determining soil
aggregation and C and N pools compared with wet sieving which increases the destruction
physical habitat of microbial habitats in aggregates and limits the
determination of water soluble C and N pools.