Characterization and Fertility Capability Classification of soils under different landforms of Dhemaji district, Assam
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Date
2023
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Abstract
The present investigation was undertaken in Dhemaji district of Assam in order to
study the physical and chemical properties of soils and to evaluate the fertility capability
classification of soils under different landforms. Three different landforms viz., piedmont
plain (P1 & P2), alluvial plain (P3, P4, P5 & P6), flood plain (P7 & P8) were selected and
horizon wise profile samples were collected from these three landforms. The study area
experienced a mean annual rainfall of 3009.19 mm and mean annual temperature of 23.16°C.
The soil temperature and moisture regime were hyperthermic and udic, respectively.
The colour of the studied soil samples in all three landforms ranges from grey to
brownish yellow with a dominant hue of 10 YR except in C1 horizon of P1 under piedmont
plain where the hue was 7.5 YR. The value ranged from 3 to 6 and chroma 1 to 6. A textural
variation ranging from sandy loam to loam in surface horizons and loamy sand to clay loam
in sub surface was observed. Sand, silt and clay contents in these soils varied from 32.35 to
85.00, 9.00 to 50.60 and 4.40 to 34.02 per cent, respectively. Higher clay content was recorded
in alluvial plain soils (34.02 per cent). Organic carbon content in the soil varied from 0.06 to
0.98 per cent, showing decreasing trend with depth with some exceptions in alluvial plain and
flood plain soils. Soil pH varied from 4.81 to 6.44. Higher pH was recorded for flood plain
soils on profile weighted mean basis. The cation exchange capacity (CEC) varied from 2.01
to 14.26 cmol (p+) kg-1 soil. On the basis of profile weighted mean, highest CEC value was
recorded in piedmont plain soils. Among the basic cations, Ca2+ was the dominant cation. Per
cent base saturation ranged from 18.07 to 62.52. The CBD extractable Al (Ald) and Fe (Fed)
varied from 0.45 to 1.30 and 0.33 to 0.86 per cent, respectively. Soils were classified as Aquic
Udorthents (P1, P7 and P8), Typic Udorthents (P5), Aquic Udifluvents (P6), Typic
Dystrudepts (P2 and P3) and Typic Endoaquepts (P4). The amount of available N, P2O5 and
K2O ranged from 12.54 (low) to 238.34 (low) kg ha-1, 2.56 (low) to 74.38 (high) kg ha-1 and
21.45 (low) to 193.24 (medium) kg ha-1, respectively. In general these nutrients tended to
decrease with depth with few exceptions. DTPA- extractable Fe, Mn, Cu status was found to
be high in all the soils and Zn was low to high. Hot water soluble B status was found to be low
to high in all the soils.
The soils of P1 (piedmont plain), P6 (alluvial plain), P7 and P8 (flood plain) were
found to be loamy (L) in type and sandy (S) in sub strata type. Rest of the pedons viz., P2
(piedmont plain), P3, P4 and P5 (alluvial plain) were loamy (L) in both type and sub strata
type. Finally after considering all the modifiers the fertility capability units were designated
as ‘LSakm(1-3)’, ‘LLakm(1-3)’, ‘LLaek(0-1)’, ‘LLak(0-1)’, ‘LLhk(0-1)’, ‘LSak(0-1)’,
‘LShkm(0-1)’and ‘LSakm(0-1)’ for P1, P2, P3, P4, P5,P6, P7 and P8, respectively.