MSc

A study entitled “Soil quality assessment and rejuvenation of coastal sandy
soils of Thiruvananthapuram district (AEU 1) through organics” was carried out
with an objective in assessment of soil quality of coastal sandy soils in
Thiruvananthapuram district (AEU 1) and development of organics based
rejuvenation methods. The study was carried out in two phases. As phase 1,
characterization of southern coastal soils of AEU 1 in Thiruvananthapuram district
was done. Based on the results of phase I, an area with low fertility was selected for
phase 2 of the study. Different organic amendments were applied to study the effect
on soil properties and crop growth in phase 2.
Fifty geo-referenced surface soil samples, along with core samples were
collected from coastal areas in AEU 1 of Thiruvananthapuram district and
characterized for various physical (texture, bulk density, particle density, water
holding capacity and soil aggregate stability), chemical (pH, EC, cation exchange
capacity, exchangeable acidity, organic carbon, available macronutrients, available
micronutrients such as Fe, Mn, Zn, Cu, B, Cl, Na and heavy metals (Pb and Cd))
and biological attributes (dehydrogenase activity and microbial biomass carbon).
Principal component analysis was used to set up the minimum data set of
indicators to compute the soil quality index. Six principal components were
extracted from which ten indicators that highly influenced the soil quality were
identified, viz. clay per cent, water holding capacity, bulk density, soil pH, organic
carbon, available K, available S, available Zn, available Mn and available B. Scores
and weights were assigned to each indicator, and were aggregated to compute the
soil quality index. The relative soil quality index of the soils were also found. GIS
techniques were used to prepare thematic maps of major soil attributes and relative
soil quality indices of the coastal sandy soils of AEU 1. Correlations were worked
out among the various analysed parameters.
The analytical results for soil physical properties showed that the predominant
soil textual class observed in the present study area was sand and loamy sand. Bulk
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density was in the range of 1.37 - 1.86 Mg m-
³, particle density 2.22 - 2.89 Mg m-
³,
with 22.7 – 56 per cent water holding capacity and 33.6-59.4 per cent soil aggregate
stability. The soil pH ranged between 5.11 - 7.19, and 0.03 - 0.23 dS m-1
for electrical
conductivity. Organic carbon was found in the range of 0.07 - 1.01 per cent, nitrogen
100 - 308 kg ha-1
, phosphorus 7.05 - 59.94 kg ha-1
and potassium 100 - 361 kg ha-1
.
Secondary nutrients ranged as: calcium 80 - 360 mg kg-1
, magnesium 47 - 152 mg
kg-1
and sulphur 4.5 - 20.5 mg kg-1
. The available micro nutrients ranged between:
6.63 - 81.57 mg kg-1
for iron, 2.53 - 36.01 mg kg-1
for manganese, 2.21 - 16.64 mg
kg-1
for zinc, 0.11 - 6.07 mg kg-1
for copper and 0.11- 0.82 mg kg-1
for boron. Heavy
metals such as Cd and Pb were below detectable limit. Soil biological activity in
these soils were poor with dehydrogenase activity in the range of 5.57 – 20.29 µg
TPF hydrolysed g-1
soil 24 hrs-1
and microbial biomass carbon of 9.18 - 29.96 µg g1
soil. So, generally the fertility status of this coastal sandy soils was found to be
low.
Majority of the soils belonged to medium soil quality (60 %), followed by
good (36 %) and poor (4 %) quality. The soils of Kadakkavoor recorded the highest
soil quality index and that of Anchuthengu, recorded the lowest.
Based on the results of phase I, a pot culture experiment was done at
Kochuveli, Industrial area, Thiruvananthapuram with Amaranthus (variety: Arun)
as test crop. The experiment was completely randomized design (CRD) with 12
treatments and 3 replications.
In the pot culture experiment, treatments included were; T1: Control, T2:
Organic POP, T3 : Vermicompost, T4: Liming + Vermicompost, T5 : Coir pith
compost, T6: Liming + Coir pith compost, T7: City compost, T8: Liming + City
compost, T9: Suchitha, T10: Liming + Suchitha, T11: FYM 12.5 t ha-1 + Biochar 12.5
t ha-1
, T12: Liming + FYM 12.5 t ha-1 + Biochar 12.5 t ha-1
. In T2 (organic POP),
FYM @ 25t ha-1
as basal dose and top dressing with fresh cow dung slurry @ 1kg
per 10 litres (50 kg ha-1
) was done. Along with that, 272.7 kg rock phosphate and
122.5 kg potassium sulphate ha-1 were applied. From T3 to T10, as per organic POP
manure recommendation, basal dose of FYM was substituted with organic
amendments @ 25 t ha-1 with or without lime application.
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Soil management using organic manures had considerable impact on growth
and yield characteristics of plant. Highest plant height was observed in T8, which
was on par with T4 and T10. Highest dry matter and yield were recorded in T10 which
was followed by T4. Effect of organic manures on quality parameters showed that
highest β carotene and nitrate content were recorded in T10. Highest vitamin C
content was recorded in T10 which was on par with T3 and T4. Being an antinutritional factor, T1 recorded the highest value of oxalate content and the lowest
was seen in T10. Regarding the nutrient uptake in plants, T10 recorded the highest
uptake of N, K, Ca and Mg, while T4 recorded the highest in P and S uptake.
Analyses of post-harvest soil for nutrient parameters showed that the highest
value of organic carbon was recorded in T10, which was on par with T8 and T9. The
highest value for available nitrogen was recorded for T10 while the highest value for
available phosphorous was recorded in T4. The potassium content was found to be
the highest in T10. Also T10 showed the highest value in available secondary
nutrients. Micronutrients analyses showed that highest content of available Fe was
present in T3, while highest of available Cu, Zn and B were recorded in T10. T9
showed the highest value in available Mn. T1 showed highest available Na and Cl
content.
Analyses of soil biological properties due to the effect of organic manure
addition showed that the highest value of dehydrogenase activity was found in T8,
which was statistically on par with T7 and T10. Also, the highest value in microbial
biomass carbon was found in T8, which was on par with T7, T9, and T10. The
highest B: C ratio was recorded by T10.
From the study, it is concluded that soil test based lime application and basal
application of Suchitha @ 25 t ha-1
, top dressing with fresh cow dung slurry @ 1kg
per 10 litres, along with 272.7 kg rock phosphate and 122.5 kg potassium sulphate
ha-1 was observed to be the best treatment to improve the soil quality, yield and
quality parameters of amaranthus in coastal sandy soils of AEU 1 in
Thiruvananthapuram district.