M Sc

The study entitled “Soil carbon storage and nitrogen dynamics in certified organic farms
of Kerala” was carried out to assess the influence of organic farming on the various physical,
chemical and biological properties and also the carbon and nitrogen pools of the soil. A field
survey was conducted and ten certified organic (certified for more than 10 years) and nearby
conventional farms representing Northern zone (Kannur), hill zone (Wayanad), central zone
(Palakkad) and Southern zone (Thiruvananthapuram) were selected for the study. Two composite
samples each from two depths (0-15 cm and 15-30 cm) were collected and analyzed for soil
properties, organic carbon pools and fractions, organic matter fractions and nitrogen fractions.
Various carbon indices like carbon pool index, lability index and management index were
worked out. For studying the temporal variation of nitrogen, samples were collected from two
certified organic farms and nearby conventional farms of College of Agriculture, Vellayani
during February, May, August and November and analyzed for various nitrogen fractions.
The soils under study belong to sandy loam, loamy sand, sandy clay and loam textural
classes. The bulk density was found to be the lowest in the organic soils (1.15 Mg m-3
) than the
conventional. Other physical properties like porosity (41.32%), water holding capacity (52.68%),
water stable aggregates (73.59%) were found to be higher in the surface soils of organic farms
than the conventional farms. Macro aggregates constituted greater proportion than micro
aggregates. The soil acidity (pH 5.71), EC (0.09 dSm-1
) and CEC (5.98 C mol (p+
) kg-1
) were
found to be more in the organic farms. Soil biological properties like soil enzyme dehydrogenase
(25.21 g TPF g-1 soil 24 h-1
) and soil protein glomalin (12.31 mg g-1
) were also found to be
higher in organic farms and decreased with depth.
The different pools of organic carbon like active (0.60%), slow (0.29%) and recalcitrant
(0.51%)) pools were found to be higher in organic farms at both depths. A higher total organic
carbon of 7.59% was registered in organic farm and it decreased with depth. Other carbon
fractions like water soluble carbon (157.79 mg kg-1
), labile carbon (2.57 mg g-1
), particulate
organic carbon (0.76%) and microbial biomass carbon (187.80 mg kg-1
) were also found to be
higher in the organic soil when compared to the conventional. Aggregate associated carbon was
166
also found to be higher in organic soil and more carbon was associated with macro aggregates
than micro aggregates. The organic matter fractions like fulvic acid (5.45%), humic acid (3.56%)
and humin (0.47%) were dominated in organic soils.
Total nitrogen content (0.46%) was the highest in organic soils. Other nitrogen fractions
like total soluble nitrogen (257.60 mg kg-1
), soluble organic nitrogen (159.3 mg kg-1
), particulate
organic nitrogen (0.51 g kg-1
), ammoniacal (121.20 mg kg-1
) and nitrate (51.80 mg kg-1
) nitrogen
and microbial biomass nitrogen (88.76 mg kg-1
) were found to be higher in organic farm than the
conventional. Total free amino acids (5.28 mg N kg-1
) and soluble protein (52.48 mg N kg-1
)
were also found to be the highest in organic soils. C:N ratio of the organic soil was found to be
16:1.
Various carbon indices like carbon pool index (0.82), lability index (0.64), management
index (0.53) and soil organic carbon stock (130.93 Mg ha-1
) were higher in organic soils than
conventional. The seasonal/temporal dynamics of nitrogen studied revealed that the highest
concentration of all the N fractions was observed during May and the least during November at
both the depths. Also a higher concentration was noticed in the organic soils than the
conventional.
From the study it is concluded that the organic farming significantly contributed to soil
carbon storage as different pools distributed in different sized aggregates of soil due to increased
organic carbon addition and aggregate dynamics. The organic matter fractions, nitrogen
fractions, carbon and nitrogen mineralization were also positively and significantly influenced by
organic management system. The soil organic carbon stock and indices were increased by
organic management system indicating the improvement in the quality and sustainability of the
system. The seasonal dynamics of various nitrogen forms and fractions were also significantly
influenced by organic farming demonstrating the interactive effect of management system and
climate change which increased nitrogen availability from organic nitrogen sources.