Soil
The
soil types of Tripura can be classified under five major groups, of which
Red loam and sandy loam soil occupies 43.07 percent of the total area
followed by Reddish yellow brown sandy soils (33.06%), the other three
groups occupy less than 10 percent each (Table-3
& Fig-3). Table-3 : Soil of Tripura
The annual average rainfall being fairly high (2000-3000 millimeters), the process of chemical weathering and rapid erosion of the soils and bed rocks appear significant. The occurrence of different soil groups can be correlated with topographical variations, land slope, climate, vegetation cover and present rock material. Dutta et.al. (1982) provided a detailed document of Soil of North Eastern Region including Tripura and showed the association of variable taxonomic units under each of the soil group, ranging between one to seven (Table-4).
1.2 Reddish Yellow Brown sandy Soil
This soil type covers nearly one third of the total geographical area of the State, mostly distributed along north south axis. Poor in nutrient, the sandy soil due to leaching under heavy rainfall, the soil type shows a resilience process through utilization of ground biomass of leaf litters. Tropical evergreen forest of Tripura largely grow in sandy soil but clear felling of trees in the hill forest can cause serious erosion problem to these soil resources. The reddish yellow brown sandy soil consist of seven soil series.
Table-4 : Reddish Yellow Brown Sandy soil
About 43-45 percent of total geographical area of Tripura is covered by the red loam and sandy loam soils. Such soil is normally associated with forest ecosystem and is rich in nutrient. In heavy rain fall area, such soil is prone to heavy erosion, specially in slope areas. Due to possible impact of deep ploughing, arable farming in red loam and sandy loam soil is not recommended specially without strict regime of soil conservation. Long cycle of Jhum cultivation is a better way of crop production in such soil zone. It is recommended also for plantation crop with adequate scope for ground cover, specially, rubber, tea, coffee and pineapple. In case of conversion of forest in such soil zone, adequate soil conservation measure is recommended. At least 14 different soil series have been identified by National Bureau of Soil Survey and Land Use Planning in red loam and sandy loam soil of Tripura. (Table-5)
Table-5
: Red
Loam and Sandy Loam Soil
1.4
Older Alluvial Soil
About 10 percent of the State is covered by older alluvial soil. Normally located in river terraces and high plains, the soil is rich in organic nutrient and suitable for arable farming. Much of older soil however remains under tropical forest cover. Due to possibility of gully erosion in uplands, slopes and river terraces, older alluvial soil need special soil conservation measures. At
least five distinct series are recognised under older alluvial soil (Table-6)
Table-6 : Older Alluvial Soil
1.5
Younger Alluvial Soil
About 9 percent of the State of Tripura is covered by younger alluvial soil, confined to the flood plains of river (e.g. Khowai, Haora, Gumti and Muhari, etc.). This composed of clay loam and loam and is extremely rich and fertile due to impact of annual flooding. While assured cultivation of Jute and Paddy in such soil regime is known, the danger of erosion by lateral cutting and bank collapse has to be kept under consideration to avoid wash-down to Bangladesh plains from the State of Tripura. River training work was recommended in the earlier “State of Environment Report in Tripura” (1989) in such soil zone.
1.6
Lateritic Soil
Along the western boundary, moorish upland with lateritic soil can be recognised. Approximately 5 percent of the total land in Tripura can be classified under “lateritic soil”. Coarse in texture and very poor in nutrients, this soil type can support scrubland and wild bushes. No arable farming or agroforestry can be undertaken in this soil condition in view of nutrient material being washed down from bedrock to lower horizon.
1.2
Soil
and Optimising Land Use
The National Bureau of Soil and land Use Planning published the results of detailed study on the issue of optimising land use based on soil features (1997) along with two maps. The finding of NBSSLUP showed some vital features. Four major land classes and seven subclasses could be identified in the state. About 19% of the area belong to class-2 and form the main food grain producing area in the south and west. Drainage is by and large the major limitations for irrigation. Both surface and subsurface drainage is restricted due to (i) very high ground water table either due to depression or other reservoirs, (ii) poor infiltration rate of soil due to high percentage of clay, silt or both. About 12% of land is grouped under class-3, which is composed of very narrow interhill valley; more than 20% land belong to class-4 where topography is major limiting factor for appropriate use, but can be made suitable for the tree crops, plantation crops, horticulture crops and spices. The issues of soil erosion and soil under flooding also come under serious concern of environmental conservation. In the State of Tripura, soil erosion factors have been grouped under 8 class categories (Table-7 & Fig.,-4). The maximum area come under class 2-2 in the middle level of erosion (26.2%), while insignificant erosion is noted in class 1-0 (19.0%) and highest level of erosion in noted in class 4-3 (10.4%)
Table-7
: Soil Erosion in Tripura
Table-8 : Soil under different flooding classes
With
regard to soil degradation, four different class categories were used
(slight/moderate/strong/extensive) but extensive degradation has never
been noted. The causes for degradation are attributed to water erosion,
chemical deterioration, and physical deterioration. Only 113,000 ha. of
soil is put under stable terrain under natural condition. Total soil area
under “strong” degradation come to 508000 ha or little less than 50 percent
of the total geographical area of the state.
1.3Physiochemical Characteristics
and Nutritional Status of Soil
Land degradation in Tripura is mainly caused by shifting cultivation, large-scale deforestation, and improper land use. An ICAR report shows a gradual decline in soil pH, organic carbon, clay ratio, available NPK and exchangeable Ca and Mg in shifting cultivation site within a three year cycle (M. Datta et.al. 1995). On the other hand, terraced agricultural land produced an appreciable rise in available NPK but fall in exchangeable acidity and available Fe and Mn contents. In the agro-forestry system, rhizosphere soil under the cover of some tree species indicate rise in soil pH, organic carbon, water holding capacity, available NPK and exchangeable Ca and Mg, but an inconsistent change in available Fe and Mn was noted. Table -9 Show some physico-chemical properties and nutritional status of soil in different land use system. Table-9 : Physico-chemical
properties and nutritional status of soil
Status of Micro Nutrients in the Soil
Status of Macro Nutrients in the Soil
Source: Department of Agriculture Cooperation and Farmer Welfare |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
