ASSESSMENT OF SOIL ERODIBILITY AND PRODUCTIVITY POTENTIAL FOR WINTER RICE IN A TRANSECT OF JIYADHOL RIVER BASIN, ASSAM
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Date
2021
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Abstract
Soil erosion is a major environmental problem in developing countries like
India, where agriculture is the main economic activity of the people. The present
investigation aims to assess the soil erodibility and productivity potential for winter rice
in a transect of Jiyadhol river basin with respect to landform characteristics,
morphometry, erosion hazard and potential for growing rice. The study area extends
from 27.335 N to 27.574 N latitudes and 94.294 E to 94.540 E longitudes, covering
an area of 47,389.13 ha. Based on topographical variation in satellite data, four distinct
landform units were delineated which includes: piedmont plain (9,097.69 ha), upper
alluvial plain (9,594.9 ha) lower alluvial plain (13,706.57 ha) and flood plain (14,977.0
ha). The drainage map identified the transect as fifth order drainage basin with higher
no‘s of first order streams making it vulnerable to erosion hazard. There was significant
variation of slope, physiographic structure and infiltration capacity across the basin. The
mean bifurcation ratio (3.56) indicated that the basin is underlined by uniform materials
and streams are branched systematically. Relatively lower value of ‗Rho‘ coefficient
indicated meager capacity of hydrologic storage during the period of floods that could
leads to higher runoff. The relatively higher drainage density (0.91 km km-2) could be
the results of impermeable subsoil material, sparse vegetation and high relief. The
drainage intensity (0.43) indicated that the basin area was highly susceptible to flooding
and gully erosion. The elongation ratio, circulatory ratio, form factor ratio and shape
factor indicated that the shape of the studied transect was nearly circular. Such basins
are highly erosion prone as compared to elongated basins.
A total of 170 no of geo-referenced surface (upto 30 cm) soil samples were
collected for analyzing soil physico-chemical, hydro-physical and fertility related
parameters. There was a decreasing trend in total sand and very fine sand content in
soils from piedmont plain toward flood plain. Whereas, silt and clay content increases
from piedmont plain towards flood plain. The textural properties of studied soils varied
from loamy sand to clay loam; sandy loam was the dominant texture. The structural
properties of studied soils varied from sub angular blocky to massive. Among the
different landform units the highest bulk density was recorded in the piedmont plain
soils (Mean 1.5 Mg m-3). The pH in the studied soils varied from very strongly acidic to
slightly acidic (4.69 to 6.47). 69.4% of the total area was strongly acidic and 4.3% of
the area was very strongly acidic. Cation exchange capacity, exchange capacity of clay,
apparent cation exchange capacity and exchangeable cations were higher in flood plain
soil which may be linked to corresponding higher clay and soil organic matter content.
Likewise, the status of soil organic carbon, available nitrogen, available phosphorus and
available potassium was high in soils of flood plain.
Soils of flood plain exhibited higher macro-aggregation owing to higher clay
and soil organic matter. However, piedmont plain soils exhibited higher microaggregate
content. Soil erodibility indices viz., silt clay ratio, clay ratio, modified clay
ratio, dispersion ratio, erosion ratio showed that piedmont plain soils are more
susceptible to soil erosion. The geospatial assessment of their variability clearly
prioritizes the areas with higher erosion susceptibility, where, suitable management
practices may be undertaken to increase soil productivity. The findings from erodibility
indices were further corroborated by soil loss assessment by universal soil loss equation,
which revealed that 38.5 percent area was under severe soil loss. The areas in higher
elevation were under higher soil loss and vice versa. The piedmont soils, affected by
very severe erosion hazard (average soil loss of 34.80 t ha-1 yr-1) which might be due to
dominating factors like higher relief, steep slope, lighter texture and weaker structure,
hence need immediate adoption of conservation measures.
The soil productivity and potentiality index was evaluated as per the procedure
suggested by Riquir et al. (1970). Piedmont plain soils having productivity index values
from 12.1 to 35.1 (Mean 23.0) were rated as poor to average classes. The acidic pH, low
organic matter, low base saturation and coarse texture being the major limiting factors
for crop production. The piedmont plain (Mean 2.01) and upper alluvial plain (Mean
1.79) soils had more coefficient of improvement as compared to lower alluvial plain
(Mean 1.60) and flood plain (Mean 1.57) soils. Majority of the piedmont plain soils are
found to be unsuitable for growing Sali, Ahu and Boro rice and the corresponding yield
of Sali rice was also quite low. Therefore alternate crops may be grown with suitable
irrigation facilities. The negative relationship of soil loss with rice yield, productivity,
potentiality and suitability indicated that greater soil loss leads to decrease in
productivity of soils. The potential productivity index value was higher for piedmont
plain soils. Significant positive relationship was obtained between normalized
difference vegetation index during peak vegetative stage with yield, soil organic matter,
mean soil site suitability index for Sali rice and crop yield index in the first year of
study
Summarizing above results it may be concluded that the Jiyadhol river basin
transect is a fifth order watershed with high vulnerability to soil erosion. Majority of the
soils of the study area have high soil erodibility owing to poor soil physical properties
as well as topographical position. Geospatial assessment of soil loss has clearly
delineated areas with severe soil loss, hence, based on this suitable conservation
measures may be effectively adopted. Moreover, while formulating site specific crop
management plan GIS based thematic maps of soil properties and erodibility may be
taken as ready reckoner to augment productivity, profitability and sustainability of
cropping systems in the area.