MSc

The study entitled ―Assessment of soil carbon pools in acid sulphate soils
of Kuttanad‖ was carried out to assess the soil carbon storage as different soil
carbon pools in acid sulphate soils of Kuttanad under different land use systems.
The study was conducted by collecting surface soil samples (0 – 15 cm) from
three agricultural land use systems namely rice, coconut and rice-fish from six
acid sulphate soil series namely Ambalapuzha, Purakkad, Thakazhi, Thuravur,
Thottapalli and Kallara. The soil samples were analysed for physical, physico-
chemical properties and carbon pools and the results were statistically analysed in
FCRD with three replications.
The soils studied belong to the textural class sandy loam to clay. The
results of the various soil parameters revealed that soil pH varied from 2.98
(Ambalapuzha series, Rice-fish) to 5.48 (Thakazhi series, Rice-fish). The highest
EC of 3.15 dS m-1 was recorded from Thuravur series under rice land use system
while the lowest from Thakazhi series under coconut land use system
(0.08 dS m-1). The exchangeable acidity was the highest in Purakkad series under
rice-fish (9.38 cmol kg-1) and it was the lowest in Thuravur series under coconut
land use (0.16 cmol kg-1). The bulk density of soils ranged from 0.68 Mg m-3
(Kallara series, Rice-fish) to 1.21 Mg m-3 (Ambalapuzha series, Coconut). Kallara
series under rice-fish recorded the highest CEC (45.50 cmol kg-1).
The results of soil carbon pools revealed that soil inorganic carbon was not
present in any of the soil series. The total organic carbon content was significantly
influenced by different land uses in all the series with the highest value of 9.38%
in Kallara series under rice and the lowest value of 1.97% in Thottapalli series
under coconut. A similar trend was observed for water soluble carbon which
ranged from 44.38 to 208.68 mg kg-1. Labile carbon in various soil series under
different land uses varied form 4.36 mg g-1 (Thottapalli series, Rice-fish) to 13.06
mg g-1 (Kallara series, Rice). Particulate organic carbon was the highest in rice
land use in Kallara series (7.23%) while it was the lowest in Purakkad series
under coconut (0.11%). The mineralised carbon values ranged from 2.17 to 2.91
mg g-1 with the highest value in Thottapalli series (Rice-fish) and the lowest in
Thuravur series (Rice).
The active and passive carbon pools and their contribution to total soil
carbon pool was the highest in Kallara series. Among the different land uses,
coconut had the highest active pool, while rice land use recorded the highest
passive pool of carbon. The humic acid content varied from 0.20% (Thakazhi
series, Rice-fish) to 6.09% (Thuravur seires, Rice) and the fulvic acid content
ranged from 0.09% (Purakkad series, Rice-fish) to 20.10% (Ambalapuzha series,
Coconut). The soil organic carbon stock and carbon pool indices were the highest
in Kallara series under rice land use and the lowest in Thottapalli series under
coconut. The proportion of POC to SOC was the highest in Kallara series under
rice land use indicating it as a potential carbon sink. The carbon turnover rate was
found to be the highest in Thottapalli series under coconut land use indicating it as
a potential carbon source.
The organic carbon stock and the carbon pools were the highest in Kallara
series followed by Thakazhi series. Among the different land uses, rice and rice-
fish contributed to maximum soil organic carbon stock and carbon pools showing
the prevalence of conducive environment in these ecosystems for the buildup of
organic carbon. This emphasizes the need to conserve the wetland ecosystems of
Kuttanad to sequester more carbon into the soil.