Taxonomy and organic carbon-nutrient interactions in selected wetland soils of Kerala
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Date
2019
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Department of Soil Science and Agricultural Chemistry, College of Horticulture, Vellanikkara
Abstract
A study was undertaken with the objective to classify wet land soils in the
agro ecological units AEU 10 (north central laterite), AEU 5 (Kole lands) and
AEU 6 (Pokkali lands) of Kerala and to assess the organic carbon stocks and
CNPS stoichiometry. The study also aimed in finding out the organic carbon -
nutrient interactions and to predict the organic carbon turnover in these soils.
Extensive field traverse was conducted to select sites for profile
excavation in the lateritic, Kole and Pokkali wetlands. The excavated profiles
were studied for their morphological, physical and chemical properties. Based on
the results of the study, soils of lateritic wetlands were classified as fine loamy,
mixed, super active, acid isohyperthermic, Fluventic Dystrustepts. Soils of Kole
lands were classified as loamy, mixed, euic, isohyperthermic, Terric Sulfihemists
and Pokkali soils as coarse loamy over sandy, mixed, active, isohyperthermic,
Typic Sulfaquepts.
Total soil organic carbon (SOC) stock in the north central laterite region
(Fluventic Dystrustepts) was 218 Mg ha-1 up to the depth of 120 cm of which
maximum amount was stored in the surface 30 cm (86 Mg ha-1). In the Kole land
soil (Terric Sulfihemists) maximum SOC was stored in the 90-120 cm layer (1016
Mg ha-1) and a total SOC of 2261 Mg ha-1 was stored up to 120 cm depth. Pokkali
soils (Typic Sulfaquepts) stored 209 Mg ha-1 SOC up to 120 cm depth which was
almost uniformly distributed in the entire profile. The C/N, C/P and C/S ratios
decreased with depth in lateritic soil profile, whereas in the Kole land soil these
ratios except C/S ratio increased significantly in the sub surface horizons. In the
Pokkali soils the CNPS stoichiometry suffered irregular variation with depth.
An incubation experiment was conducted to study the organic carbon
nutrient interactions in the three wetland soils. Treatments included control (T1),
POP based fertiliser and lime application (T2), soil test based fertiliser and lime
application (T3), FYM substituting nitrogen in the T3 treatment (T4) and soil test
based fertiliser and dolomite application (T5). In the lateritic soils. the active
carbon and organic reserves of N, P and S were high in T3 treatment. The organic
N, P and S pools increased in treatment T5 whereas organic P and inorganic S
increased in treatment T4. In the Kole land soils, active carbon, organic nitrogen,
inorganic P, organic S and inorganic S increased in T3; inorganic N and organic P
increased in T4 and organic P and S pools increased in T5. In the Pokkali soils,
active carbon content was high in T2 compared to other treatments while active
carbon, organic N and inorganic N decreased in treatment T3. Liming decreased
organic P in Pokkali soils due to conversion to available forms and higher
utilisation. Application of FYM increased organic S in Pokkali soils and inorganic
S in all soils.
Temporal variation of the nutrient content (mg kg-1 soil) per organic carbon
content (g kg-1 of soil) indicates the change in nutrient supply per unit change of
organic carbon content. Treatment T1 favoured higher inorganic nitrogen per
carbon content in laterite and Pokkali soils, where as in in Kole soils it was
increased in T4. Inorganic phosphorus content per carbon was highest in laterite
and lowest in Kole soil in control (T1). Inorganic sulphur per carbon content was
highest in T4 for laterite, Kole and Pokkali soils. Organic nitrogen per carbon
content was highest in the Kole land and minimum in the Pokkali land in the T3
treatment. Organic phosphorus per carbon content was maximum in FYM
treatment in Kole and Pokkali soils and was minimum in T2 treatment in laterite
and Pokkali soils. Treatment T3 had the highest organic sulphur per carbon
content in the laterite and Kole soils and the treatment T1 gave the highest content
in Pokkali soil.
Wetland DNDC model was used to simulate the organic carbon turn over
in the three wetland systems using the climatic data predicted by MarkSIM
software. The results of modelling simulated for the year 2050 indicated that
application of 100 per cent NPK along with FYM @ 5t ha-1 will ensure maximum
organic carbon content in the Kole, Pokkali and lateritic wetlands. Fertiliser
application improves the organic carbon storage in lateritic and Kole land soils.
But in the Pokkali soils, fertiliser addition will not cause change in the organic
carbon turn over processes whereas FYM application can improve the carbon
content.
Results of the study indicate that cultivation without any fertiliser and lime
application causes gradual depletion of all organic and inorganic pools of
nutrients in Kole land and lateritic wetland soils. Soil test based fertiliser and lime
application along with FYM @ 5t ha-1 is appropriate in these soils for increased
sustainability. The Pokkali soils are self-sufficient and can sustain its fertility
status without any fertiliser application. However liming and FYM application
may be considered as management options to improve sulphur availability and
organic carbon turn over processes in these soils.
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174738