MSc

ABSTRACT
The study entitled “Assessment of soil quality in the post-flood scenario of
AEU 12 in Pathanamthitta district of Kerala and generation of GIS maps” was
undertaken with the objectives of evaluating soil quality in the post-flood area of AEU
12, formulation of soil quality index and generation of GIS maps of soil characters
and quality. A survey was conducted during April 2019 in the study area and seventy
five georeferenced surface soil samples were collected from eight flood affected
panchayaths viz., Kalanjoor, Pramadom, Konni, Pathanamthitta municipality, Ranni-
Angadi, Vadaserikkara, Ranni-Perunadu and Naranammoozhi. The major land use
systems in the study area were intercropping of banana with tapioca and vegetables,
banana with tapioca, coconut with tapioca, coconut with banana, tapioca with
vegetables, and sole cropping of banana, tapioca, coconut, vegetables, rubber and oil
palm and other crops like cocoa, arecanut, pepper, nutmeg, mangosteen elephant foot
yam etc. Most of the farmers apply lime and chemical fertilizers in coconut, banana,
cassava and rubber. Vegetable cultivation is mostly organic using indigenous nutrient
sources.
The samples were characterized for selected physical, chemical and biological
attributes. A minimum data set (MDS) of indicators to assess soil quality was set up
using Principal component analysis (PCA). PCA yielded six principal components
with eigen value >1 from which highly weighted parameters were selected for the
MDS. The MDS consisted of nine parameters viz., sand and silt per cent, bulk density,
soil pH, available P, available K, available B, available Mg and acid phosphatase
activity. A weighted soil quality index was formulated using the MDS following
standard procedures. Land quality index and nutrient indices for organic carbon and
available primary nutrients were also worked out. Spatial variability in soil characters,
SQI, LQI and NI were mapped using GIS techniques. Status of soil properties and soil
quality under different land uses were also assessed and correlations between the
analysed parameters were computed.
Deposition of sediments was observed in Ranni-Angadi, Naranammoozhi,
Vadaserikkara and Ranni-Perunnadu in the area close to the Pampa river. Majority of
the area had a BD <1.2 Mg m-3 (65.3%), PD <2.2 Mg m-3 (42.7%), porosity between 50 and 70 per cent (56%), soil moisture content between 15% and 25% (36.0%), water
holding capacity between 30 and 50 per cent (57.33%), WSA (%) >70 per cent
(54.7%) and MWD >2mm (40.0%). The predominant soil textural class in the study
area was sandy clay loam. Soil pH was very strongly acidic for 25.3 per cent of the
area and extremely acidic for 22.7 per cent. EC was <1 dS m -1 for the entire area.
Organic carbon was high for 50.7 per cent of the area. Available N was low and
available P was high for more than 80 per cent of the area. Available K was in the
medium range for 58.7 per cent of the area. Available Ca, Mg and S were adequate
and available B deficient for most of the area. Acid phosphatase activity was between
25 and 50 μg PNP produced g soil-1 h-1 for 44 per cent and between 10 and 25 μg PNP
produced g soil-1 h-1 for 42.7 per cent of the area.
Medium soil quality was obtained for 54.7 per cent of the area and good for 36
per cent. The highest mean was for Naranammoozhi (283), followed by Ranni-
Perunadu (278), Vadasserikkara (278) and Ranni-Angadi (272). Land quality was very
low for more than 60 per cent of the area. Nutrient indices for available N, P and K
were low, high and medium respectively for the entire area. Nutrient index for organic
carbon was high except for Vadaserikkara, Naranammoozhi and Ranni-Perunnadu
(medium). Soil quality index was found to be the highest for the land use involving
intercropping of banana with tapioca and vegetables.
Comparison with the pre flood data of KSPB (2013) showed an increase in the
percent of samples with extremely acid, slightly acid and neutral pH, a decline in the
percent of area with high organic carbon and available K. Per cent of area with
adequate levels of available Ca were similar in the pre flood and post flood study
whereas percent of area with adequate available Mg and S declined. Area with
adequate available B and high available P showed an increase in the post flood study.
Thus, the present study shows that site specific soil management based on
current nutrient status, cropping system and periodic interventions for quality
assessment will help in achieving higher productivity and sustainability. Increase in
soil acidity in areas which experienced erosion and moderation of pH in areas of
deposition and variations in the status of organic carbon, available P, K, Mg, S and B
compared to pre flood study necessitate a revision in soil management practices.