MSc

The study entitled “Soil quality and biological resilience of AEU 17 (Marayur
Hills) of Kerala” was carried out with the objective of characterization and assessment of
soil quality, development of thematic maps and to explore the soil biological resilience
of AEU 17 (Marayur Hills) of Kerala to transient (heat) and persistent (Cu induced) stress.
Sixty geo referenced surface (0-15 cm) and subsurface (15-30 cm) soil samples
were collected and analyzed for physical (bulk density, particle density, texture porosity,
water holding capacity, soil moisture content and aggregate analysis), chemical (pH, EC,
exchangeable acidity, organic carbon, available macronutrients, available Fe, Mn, Zn, Cu
and B) and biological (acid phosphatase and dehydrogenase activity) attributes. Ten
surface samples from each of four major land use systems (forest, sugarcane, cool season
vegetables and fruits) were bulked together to make single representative sample to
explore biological resilience.
A weighted soil quality index was formulated based on minimum data set (MDS)
of soil physical, chemical and biological parameters derived through principal component
analysis (PCA). The PCA gave six principal components for surface soils (0-15 cm) with
eigen value greater than 1, which yielded nine parameters viz., organic carbon, available
copper, per cent sand, available sulphur, electrical conductivity, available magnesium,
boron, calcium and per cent silt. For subsurface soils (15 – 30 cm), PCA gave seven
principal components with eigen value greater than 1, which yielded ten parameters viz.,
organic carbon, per cent clay, available manganese, pH, available sulphur, boron, iron,
magnesium, per cent silt and available calcium. Parameters in MDS were classified,
scored and weights assigned based on current soil characteristics, agricultural systems,
and agro climatic variables. The relative soil quality indices were computed. Nutrient
indices of organic carbon and available primary nutrients were calculated. GIS maps were
generated to depict the spatial variability in soil properties, quality and nutrient indices.
Correlations between the analyzed parameters were worked out in both surface and
subsurface layers.
Sandy clay loam was the predominant (40 %) soil textural class observed in the
study area, followed by clay (33.3 %), sandy loam (16.7 %) and clay loam (10 %). Soil
pH was slightly acidic in the surface (54 %) and subsurface (50 %) soils with a slight
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depth wise decrease. No such depth wise variation was observed for electrical
conductivity which indicated their non-saline nature (< 1dS m-1
). Exchangeable acidity
of 90 per cent surface soils was less than 0.5 cmol (+) kg-1 whereas majority of subsurface
samples (83.3 %) ranged between 0.5 and 1.0 cmol (+) kg-1
. Available N was low (< 280
kg ha-1
) in majority of samples in both surface (53 %) and subsurface (63 %) soils.
Available P (>24 kg ha-1
) and K (>275 kg ha-1
) status were high for majority of both
surface and subsurface soils. Surface (83 %) and subsurface (67 %) soils were sufficient
in available Ca. Majority of surface (67 %) soils showed sufficiency in available Mg
while it was deficient in 63 per cent of subsurface soil samples. Available sulphur status
was sufficient for all the samples in both surface and subsurface layers. All micro
nutrients except B indicated sufficiency.
Relative soil quality index was high for all the surface soil samples while 76 per
cent of sub surface soil samples showed good relative soil quality index and 23.3 per cent
samples showed medium relative soil quality index. Nutrient indices were high for OC,
available P and low for available N in both surface and subsurface soils in all the
panchayaths. Nutrient index for K was high for surface soil in all panchayaths. Though it
was high in subsurface soil of Vattavada panchayath, it was medium in both Marayur and
Kanthalloor panchayaths. Majority of the soils in surface (67 %) and subsurface (63 %)
layers showed very low land quality index.
Biological resilience assay for transient heat stress and persistent copper stress in
different land use systems revealed that forest soils showed high stability index and
resilience index for both heat and copper induced stress. This was followed by sugarcane
and cool season vegetable land use systems which also exhibited an increase in respiration
expressed in terms of carbon mineralization potential after 21 days of incubation. Fruits
land use system showed low value for both soil stability index and resilience index for
applied heat stress. Fruits land use system exhibited a progressive decline in both stability
index and resilience index over a period of 21 days of incubation.
Maintenance of a high soil quality index is a pre-requisite for soil health.
Assessment of soil quality index on a regular basis would facilitate adoption of effective
alternate site-specific management of crops. Liming of acid soils, regular application of
recommended doses of nitrogenous fertilizers, application of phosphorous and potassic
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fertilizers in P and K deficient areas, applications of borax at regular intervals are the
suggested interventions in AEU 17 (Marayur Hills). Integrated application of organic
manures along with inorganic fertilizers is to be encouraged in the fruits land use system
for enhancing the soil biological resilience to transient and persistent abiotic stress as is
evident in the forest land use system.