Pa. Jacinthe et al., Organic carbon storage and dynamics in croplands and terrestrial deposits as influenced by subsurface tile drainage, SOIL SCI, 166(5), 2001, pp. 322-335
Soil erosion contributes to the removal of soil organic carbon (SOC) from c
ultivated soils and its entrapment in terrestrial depressions. The fate of
SOC entrapped in terrestrial deposits is largely unknown, but there has bee
n speculation that such entrapment could lead to C sequestration, thereby p
laying a role in global C cycling. It has been hypothesized that the fate o
f eroded C in these deposits depends on SOC quality (bioavailability) and t
he environmental conditions at the depositional site. The SOC storage and d
ynamics were studied in cultivated, forested, and deposited soils at sites
with and without subsurface tile-drainage. Microbial biomass carbon (MBC),
readily mineralizable C (MinC), and basal soil respiration (BSR) rates were
used as SOC quality indicators and were assessed in field-moist soil aggre
gates of four sizes: 2-3 nun, 1-2 mm, 0.5-1 mm and <0.5 mm. Soil organic ca
rbon inventory (mass of C over the depth sampled) was significantly differe
nt (P < 0.01) among the land uses and was in the order: deposit > forest >
cropland. It was also significantly (P < 0.1) different between the two dep
osits, amounting to 14.6 and 17.1 kg C m(-2) in the tile-drained and undrai
ned deposits, respectively. Over that same depth, the total SOC pool in the
forest soil was 9.5 kg C m(-2). Overall, the various aggregate sizes did n
ot differ significantly in terms of their total SOC content, but the SOC qu
ality indicators (MBC, MinC, and BSR) were generally higher in the larger t
han in the smaller aggregates. These indices were also higher in the forest
and depression sites than in the croplands. The data indicated that cultiv
ation and erosion resulted in depletion of both total and labile SOC, but t
he labile pools were depleted at rates 1.5 to 3 times faster. Conversely, t
here was an enrichment in both clay (1.4 to 2 times) and SOC (1.3 to 1.6 ti
mes) in the depression areas, indicating removal of fine particle-associate
d SOC from the cultivated fields and its entrapment in the deposits. Howeve
r, the levels of labile C (MBC, MinC) in the entrapped materials were 20 to
46% lower than would be anticipated based on their total C contents. These
reductions suggest that, compared with the forest and cropland, a relative
ly greater proportion of the C retained in the deposits is in the slow and
passive pools, and that distribution is favorable to sequestration of C in
these landscape positions. (Soil Science 2001;166:322-335).