MSc

The study entitled “GIS approach for quality assessment and mapping of acid
saline (Kaipad) soils under agricultural land uses” was undertaken during 2019-21 to
assess the soil quality and develop thematic maps on soil characters using GIS
techniques. A survey was conducted in the Kaipad area (AEU-7) of Kannur, Kasargod
and Kozhikode districts of Kerala and 126 representative georeferenced surface soil
samples (0-20 cm) were collected from different agricultural land use systems
prevailing in that area viz. rice, rice – shrimp, mangrove, coconut and fallow
belonging to 10 soil series. Twenty five water samples were also collected and
analysed for quality parameters.
The soil samples were assessed for various physical, chemical and biological
properties and a weighted soil quality index was formulated based on a minimum data
set (MDS) of parameters obtained by using principal component analysis (PCA). The
PCA gave six principal components with eigen value greater than 1, which yielded
nine parameters viz., pH, EC, organic carbon, available N, P, K, Mg, B and Zn.
Parameters in MDS were classified, scored and weights were assigned based on
current soil characteristics, agricultural systems, and agro-climatic variables. Nutrient
indices of organic carbon and available primary nutrients were also calculated. GIS
maps were generated to depict the spatial variability in soil properties, quality and
nutrient indices.
Soil properties analysed were interpreted at panchayath and land use levels and
correlation analysis were carried out between soil characteristics. Majority of the soils
recorded a bulk density < 1.20 Mg m-3 (100%), particle density between 2.40 and 2.60
Mg m-3 (44%), porosity between 50.0 and 70.0 per cent (86.5%), maximum water
holding capacity between 30.0 and 50.0 per cent (52.4%) and MWD <1 mm (80.2%).
Sandy clay loam was the predominant soil textural class in AEU 7.
Majority of the soils (45.2%) showed extremely acid pH (<4.50). 81.7 per
cent of samples had EC between 0.00 to 2.00 dS m-1. Available N was low in 94.4 per
cent samples, available P medium in 41.3 per cent samples and available K low in 46
per cent samples. Available Ca, Mg and B were deficient in 61.1 per cent, 100 per
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cent and 53.2 per cent samples respectively. Available S and cationic micronutrients
like Fe, Mn, Cu and Zn were sufficient in most of the soils. Fe and Al toxicity were
observed for 20.6 and 26 per cent of the soils respectively. Heavy metals (Pb, Cr, Cd
and Ni) were below maximum permissible limit. Organic carbon was high in 57.1 per
cent of samples, MBC between 100 and 300 µg g-1soil in 93.7 per cent samples and
dehydrogenase activity between 1500 and 2500 µg TPF released g -1 soil 24 hr-1 in
83.3 per cent samples. The soil quality was found to be medium in 88.2 per cent of the
area. Nutrient indices were high for organic carbon, low for available N, and medium
for available P and low for available K in AEU 7.
A significant variation among land uses were obtained for the soil parameters
like soil moisture content, maximum water holding capacity, moisture content at field
capacity, electrical conductivity, available N, Fe, B, Si, organic carbon and microbial
biomass carbon whereas the other parameters did not vary significantly between land
uses.
With regard to water quality, pH was found to be <6.5 in 52 per cent samples
and EC was rated low (<2.5dS m-1) for 48 per cent of water samples and very high
(22.5 – 50.0 dS m-1) for 28 per cent samples. SAR was <10 in all water samples, SSP
was between 40 and 60 per cent and RSC < 1.25 meq/L in most of the samples which
was suitabile for irrigation. The concentration of heavy metals (Pb, Cr, Cd, Ni) was
found to be above the critical limits in water samples.
The acid saline soils of Kaipad (AEU 7) under different agricultural land uses
are strongly to extremely acidic with high EC, deficiencies of N, K, Ca, Mg, B and Fe
and Al toxicity which requires liming, addition of N, K, Ca, Mg and B to enhance
productivity.