wAbstract
@The study was conducted to quantify the relationships between
soil texture (silt + clay) and soil organic carbon (SOC) or total
nitrogen (TN) under native forests and rice-wheat cropland in
the eastern Indo-Gangetic Plains. Soils were collected from 99
native ecosystem sites and 22 cultivated rice-wheat (RW) sites
in Nepal and Bangladesh at 15 cm depth increments to a depth of
60 cm. Surface layer (0-15 cm) samples were collected from an
additional 266 cultivated sites in Nepal and Bangladesh. Positive
relationships between soil silt + clay and both SOC and TN were
established for each depth increment. The data were best fit by
exponential functions which, together with bulk density values,
were used to estimate SOC and TN stocks as a function of depth
and soil texture. The conversion of forests to rice-wheat cropland
resulted in mean reduction in SOC stocks of 55, 32, 17, and
10 in the 0-15, 15-30, 30-45, and 45-60 cm depths,respectively.
It appeared that fertilizer N inputs had affected mean TN stocks,
as N loss upon conversion to cropland was only found for the 0-15
cm depth, and there were significant N gains below 30 cm soil
in the cultivated rice-wheat fields. Soil silt + clay content
had a large effect on losses of SOC with cultivation, which were
estimated to increase from 10 to 33 Mg ha-1 for the
0-60 cm depth over the silt + clay range from 250 to 1000 g kg-1.
The SOC losses on cultivation also represent the potential to
sequester C in these soils, which is similarly dependent on soil
texture. Between 76 and 87, of the total (0-60 cm) C sequestration
potential is estimated to occur in the top 30 cm of the soil profile
over the range in silt + clay from 250 to 1000 g kg-1.
For the mean texture of rice-wheat soils, the C-sequestration
potential was estimated to be 22.2 Mg C ha-1 for the
0-60 cm depth, with 86 of this potential occurring in the top
30 cm of the soil profile.
Keywords: Texture; Soil organic carbon; Total nitrogen; Indo-Gangetic
Plains; Rice-wheat system; Carbon sequestration potentialx
1. Introduction
2. Materials and methods
3. Results
@3.1. Soil texture-organic carbon and total nitrogen relationships
@3.2. Changes in soil organic carbon and total nitrogen after
cultivation
@3.3. Effect of soil texture on SOC and TN changes with cultivation
4. Discussion
@4.1. SOC and TN relationships with soil texture
@4.2. Changes in SOC and TN with cultivation
@4.3. Implications for carbon sequestration
5. Conclusions
Acknowledgement
References