MSc

ABSTRACT
A study entitled “Soil biodiversity under organic and integrated nutrient
management systems and impact on soil quality” was carried out with an objective
to characterize soil biodiversity in coconut based cropping systems of southern
laterites (AEU-8) of Kerala under organic and integrated soil management and to
correlate soil biodiversity with soil quality and plant nutrient availability. The study
involved soil sample collection and characterization of soil samples for soil
biodiversity and soil properties.
Soil samples were collected from coconut-based cropping systems under
organic soil management in the Model Organic Farm, Department of Soil Science
and Agricultural Chemistry, College of Agriculture, Vellayani (Site 1) and also
from coconut-based cropping systems under integrated nutrient management in the
Instructional Farm, College of Agriculture, Vellayani (Site 2). From each site, 10
composite soil samples each were collected from 0-15cm, 15-30cm and 30-60 cm
depth.
Soil samples were characterised for soil macro, meso and micro fauna,
microflora and beneficial microorganisms. Soil biodiversity was estimated from a
single, pooled sample of each site. The soil samples were analysed for their physical
(soil texture, bulk density, particle density, porosity, soil moisture content and water
stable aggregates), electrochemical properties (pH and EC), chemical (cation
exchange capacity, anion exchange capacity, Total N, P, K, S, available N, P, K,
Ca, Mg, S, B, Fe, Mn, Cu, Zn and organic carbon) and biological properties
(microbial biomass carbon, dehydrogenase activity and amylase activity).
Among the soil macrofauna, annelids, hymenopterans, isopods, dermapterans,
myriapods and carabids were observed. Annelid population was highest in the
surface soil of site 1 (40 no.m-2
) and these varied significantly among the
managements across all depths. Hymenopterans were observed only in surface soil
and were found to be significantly higher in site 1 (6 no. m-2
). Isopods were found
only in surface soil of site 1 (1.33 no. m-2
) and were not observed in site 2. The
count of dermapterans were found to be higher in site 1 but there was no significant
difference observed among the managements. Myriapod population (millipedes and
centipedes) were observed only in the surface and subsurface soil of site 1. Carabids
(ground beetle) were observed only in the surface soil of site 1.
Among mesofauna, both acari and collembola were higher in the surface soil of
site 1 (3983.33 no. m-2
and 4939.33 no. m-2
respectively). Acari population varied
significantly among the managements at 0-15 and 15-30 cm soil depth while
collembolans varied significantly across all depths. Soil microfauna (nematodes)
was higher in the surface soil of site 1 (231830 no. m-2
) and their population varied
significantly among the managements across all depths.
Soil microflora including bacteria, fungi, and actinomycetes were found to be
higher in the surface soil under organic management (42.6 x 105
cfu g-1
, 18 x 103
cfu g-1
, 36 x 103
cfu g-1
respectively). Significant difference among both
managements were found in abundance of all organisms at each depth except for
fungi at 30-60 cm. Beneficial microorganisms including Azospirillum, Phosphate
Solubilizing Bacteria (PSB) and K solubilizers were cultured and enumerated from
both soil managements. The population of Azospirllum was higher in the surface
soil of site 1 (7 x 103
cfu g-1
) and these varied significantly among the managements
at 0-15 cm and 15-30 cm soil depth. The count of PSB and K- solubilizers obtained
in the culture media was too low to be recorded.
The soil texture was found to be sandy clay loam for soil samples collected
from both sites. The sand fraction was observed to be decreasing with depth, while
silt and clay fractions increased with increase in depth. Significantly lower bulk
density was observed in organic field (1.31 Mg/m3
in surface soil) at all depths and
it increased with increase in depth. Higher particle density was observed in the
surface soil of site 1 (2.34 Mg/m3
) and no significant difference among the samples
was observed at any depth. Higher porosity was observed in surface soil of site 1
(46 %) and it varied significantly among the managements across all depths. The
mean soil moisture content was observed to be slightly higher in soil under INM at
all depths, but no significant difference between the managements were observed.
Water stable aggregates were higher in surface soil of site 1 (69.34 %) and it varied
significantly among the managements across all depths.
All the chemical properties except pH was found to decrease with increase in
depth. The surface soil of site 1 recorded the significantly higher mean values for
EC (0.21 dS m-1
), CEC (6.97 C mol (p+
) kg-1
), total N (1986.88 kg ha-1
), total P
(969.92 kg ha-1
), total K (1512 kg ha-1
), total S (947.52 kg ha-1
), available P (88.03
kg ha-1
), available K (361.20 kg ha-1
), available Zn (2.83 mg kg-1
) and OC (0.96 %).
All these properties showed significantly higher mean values in site 1 across all
depths. The surface soil of site 2 recorded significantly higher mean values for pH
(5.57), available N (222.5 kg ha-1
), B (0.436 mg kg-1
), Fe (16.79 mg kg-1
) and Cu
(0.99 mg kg-1
). These properties varied significantly among the managements
across all depths, except available B at 15-30 cm and 30-60 cm, and available Cu
at 30-60 cm. While AEC, available Ca, Mg, S and Mn did not show significant
difference among the management at any depth.
The surface soil of site 1 recorded higher microbial biomass carbon (22.96 μg
g
-1
), dehydrogenase (31.02 μg TPF hydrolysed g-1
soil 24 hr-1
) and amylase (1.24
mU g-1
of soil) activity. All these biological properties decreased with increase in
depth and were observed to be significantly higher in soil under organic
management at all depths.
Organisms observed a positive correlation with most of the physical, chemical
and biological properties of soil. Negative correlation was observed between soil
organisms and bulk density and also between hymenoptera and dermaptera with
soil pH.
From the Bray Curtis dissimilarity index, it is observed that the average
dissimilarity of biodiversity was 0.262 between the surface soil of organic
management and INM. This suggests that there are differences in species
composition, although there are also shared species or similarities to some extent.
Average dissimilarity among the managements decreased with depth. The
PERMANOVA analysis showed that "depth" had a substantial and statistically
significant effect, while the "management" factor did not significantly contribute to
community dissimilarity. The interaction term "management × depth" also proved
to be non-significant in explaining community dissimilarity. From the Bray Curtis
dissimilarity index SIMPER analysis was performed and it showed that nematode
is the species that contributes the largest amount of the difference between 0-15 cm
and 15-30 cm soil depths and also between 15-30 cm and 30-60 cm soil depths.
From this study, it was concluded that soil biodiversity was positively
correlated to most of the soil properties and no significant effect was observed in
the community dissimilarity for management but, depth had a substantial and
statistically significant effect on community dissimilarity.