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IAPRS & SIS, Vol.34, Part 7, “Resource and Environmental Monitoring”, Hyderabad, India, 2002
For crop production, the relative importance of each horizon in
soil profile varies. The importance of a horizon becomes greater
when its position is nearer to the surface (Sys, 1993). Therefore,
weighted mean (WM) of various land qualities (like electrical
conductivity (EC), pH etc.) of each soil series were computed
and considered for land evaluation. For this, the profile was
sub divided into sections and to each of these sections, a depth
correction index (weightage factor) starting with a minimum
value at depth and gradually increasing towards the surface was
attributed.
3. RESULTS AND DISCUSSION
3.1 Image interpretation
For delineating soil-landscape units primarily summer season
(May, 98) FCC of the merged data of IRS-IC PAN and LISS III
was used in conjunction with topographical maps. The summer
season data depicted the bare soil devoid of crop cover, which
helped in ascertaining the differences in soils. Moreover, help
of winter season (Jan, 1997) FCC of the merged data was also
taken to reconcile the differences in various soil-landscape
units. In the merged data of both seasons the various cultural
features were quite conspicuous, as it maintained the spectral
context of multispectral image (LISS-III) at the spatial
resolution of higher resolution image (PAN), enhancing the
interpretability of satellite data (Saraf, 1999).
As the degree of soil salinity/sodicity influences the spectral
behaviour of soils (Singh and Dwivedi, 1989, Rao et.al., 1995)
and also the land cover and land use pattern (Sharma et.al.,
2000) the image exhibited different tones, textures and pattern.
These image characteristics with information on land use and
other ground data were interpreted to identify and delineate
spectrally differing classes.
Physiographically the study area was divided into three units
namely old tidal plains, swale plains and beach ridges. Among
the old tidal plains normal soils appeared as smooth continuous
dark tone in summer season data while in winter season data it
appeared as smooth bright orange and pink (interspersed with
dark green patches) in rectangular shaped fields indicating a
normal growth of crops like cotton and pulses (with fallows).
Among swale plains, moderately saline soils appeared as
smooth white and light gray patches in summer season data
while in winter season data also it appeared as smooth white
with light blue patches. The moderately saline-sodic soils had
continuous coarse light gray tone with white mottles in summer
season data while in winter season data it appeared as coarse
light bluish in rectangular shaped fields with reddish black tone
in winter season data. The slightly saline sodic soils appeared
as coarse light red in summer season data and coarse continuous
red tone in winter season data. In the swale plains mainly paddy
crop was cultivated which was also evident from the series of
yellow mottles visible on the summer data, implying harvested
staked bundles of paddy arranged orderly in the field.
The beach ridges were divided into fallow, plantation, dense
scrubs and open scrub based on land use/land cover.
Mudswamp appeared as continuous, smooth black in
association with canals whereas fishponds (prawn cultivation)
and saltpans appeared as rectangular, smooth black, bluish and
white in patches associated with stream and canals.
3.2 Soils of the study area
The soils of the study area were mapped based on image
interpretation, soil-landscape studies, ground data and
laboratory analysis of soil samples. The soil map was prepared
on 1:25,000 scale. It depicted the extent and distribution of soils
occurring in the study area at series level. The description of the
soils including soil-landscape unit, classification, series, land
use and other features is given in Table 1 below.
SI.No | Soil landscape | Series Classification Soil description
unit
Old tidal plain
+ Normal soil Yamleru ' Fineloamy Typic | Cultivated, very deep, moderately well drained, silty clay loam
with saline sub Haplustepts soils with slight erosion on 0-1 percent slope.
soil
2. Normal soil Uppu-1 Fine Typic Cultivated, very deep, moderately well drained, sandy clay soils
with saline sub Haplustepts with slight erosion on 1-3 percent slope.
soil
Swale plain
3. Mod. Saline Agam Coarse loamy Fallow, very deep, well drained, sandy loam soils with slight
Typic Ustorthents | erosion on 0-1 percent slope.
4. Slightly saline Mettegunta | Fineloamy Typic | Cultivated (Paddy), very deep, moderately well drained, clay
sodic Haplustepts loam soils with slight erosion on 0-1 percent slope.
5 Mod saline & Uppu-2 Fine loamy Typic | Cultivated (Paddy), very deep, moderately well drained, sandy
sodic Haplustepts clay loam soils with slight erosion on 0-1 percent slope.
Beach ridges
6 Fallow Gollapalem | Typic Very deep, excessively drained, sandy soils with slight erosion on
Ustipsamments 1-3 percent slope with fallow.
7 Plantation Gollapalem | Typic Very deep, excessively drained, sandy soils with slight erosion on
Ustipsamments 1-3 percent slope with plantation.
8 Dense scrub Gollapalem | Typic Very deep, excessively drained, sandy soils with slight erosion on
Ustipsamments 1-3 percent slope with dense scrub.
9 Open scrub Gollapalem | Typic Very deep, excessively drained, sandy soils with moderate
Ustipsamments erosion on 1-3 percent slope with open scrub.
Table.1 Description of soils of the study area.
