The Soils

Distribution and Classification of Soils

Characterisation of Soils Under Different Agro -Ecological Subregions

Soil Resource Mapping

Manipur is endowed with wide range of climates, physiographic settings, geology and vegetative sequences. The interaction amongst these factors in the ecosystem with time and space leads to result in the formation of different kinds of soils with different properties, limitations and potentials.

The field survey was conducted following physiographic sequences of the terrain features. the survey included profile studies at different geographic situations, checking and sampling of auger-bore samples at 10 km intervals of grid points, and in addition, random checking of soils at different sites to generate soil mapping units (soil family associations ) showing soil physiographic and climatic relationship.

The map units (soil family association) have been described area-wise and in a manner that have been described area- wise and in a manner that most of the land users can understand. the descriptive legends describing the mapping units have been given in detailed report the taxonomic names of each of the soils(following Soil Taxonomy, Soil Survey Staff, 1975) have been given in the secondary place of the phases of dominant and subordinant soils in the mapping units as also of the inclusions (if any) have been illustrated in Extended legend is also given on the coloured soil map.

Distribution and Classification of Soils

The soil of Manipur belong to 4 orders, 8 suborders, 13 greatgroups and 23 subgroups.  It is observed that the Inceptisols are the dominant soils followed by Ultisols, Entisols and Alfisols and occupy 38.4%, 36.4%, 23.1% of the total geographical area of the State, respectively. Lake and marshy land occupy 1.9 percent.The  area- wise distribution of soil at order and suborder levels of Taxonomy are given below.

1. Distribution of Soil Order and Sub-orders of Manipur

TGA:Total Geographical Area

2. Area distribution of different soil Orders, Suborders, Greatgroup and Subgroups in Manipur

Characterisation of Soils Under Different Agro -Ecological Subregions

The state comes under the hot and warm humid/per-humid agro-eco region. However, at microlevel, it can be divided into three distint-subregions(zone) with thermic and hyperthermic temperature regimes as follows:

LGP : Length of Growth Period

1.Warm-humid agro - eco zone with thermic ecosystem and LGP 300-330 days.

2. Hot -humid agro - eco zone with hyperthermic ecosystem and LGP 270-300 days.

3. Warm Per-humid agro- eco zone with thermic ecosystem and LGP 330-365 days.

 Table : Description of Agro ecological Sub-regions

1.Soils of Warm Humid Agro-Eco Zone with Thermic Ecosystem(with LGP 300-330 Days)

The soils are derived from shale and sandstone and mostly occur on the hills of varying slopes. Soils occuring on the gently sloping foot hills are deep, well drained with greyish brown to yellowish brown in colour. Soils are classified as Type Haplohumults, Umbric Dystrochrepts and Ultic Hapludalfs.

Soils on steep to very steep hill slopes are deep under thick vegetative cover and otherwise they are shallow with exposed stratified grey coloured shale layers. The soils are classified as Typic Kanhapludults, Umbric Dystrochrepts. Typic Udorthents, Typic Haplohumults and Typic Hapludults.

The soils are acidic with high organic matter content. Available phosphate is very low in the soils of upper reaches while it is very low in the soils of upper reaches while it is medium in the soils of narrow valleys which may be due to the formation of Ferric(Fe³⁺⁾ phosphate or organometalic complexes not easily available to plant.

Valley and fllod plain soils derived from alluvium are deep to very deep, poorly to moderately well draiend. The soils are slightly acidic to neutral with high humus content. The ground waterable is generally high and the soils are classified as Typic and Mollic Haplaquepts, Fuvaquentic Humaquepts, Typic Haplaquent and Typic Fluvaquents.

Land Use  

The upper reaches of the hills are under forest cover of decidous trees while mixed forest species comprising bamboos, wild bananas etc. occur in the lower steep hills. Jhum cultivation is practiced in places of convenient slope grades on medium hill ranges in normal cycles of 5-10 years. Maize, Sesamum, potato, Ginger, Tapioca and vegetables are grown under the shifting cultivation system. Horticultural crops like Orange, Pineaple, Lemon, etc. are also terraced on hill slopes and used for permanent cultivation.Scars of Jhum fields with secondary growth of vegetation are commonly occured. Valley lands are generally well bunded and used for intensive and permanent agriculture. The ' beel' areas are occupied by luxurient growth of submerged weeds of mixed species.    

Soil Constraints and potentials

The salient problems and potentials of the soils are:

Constraints : Hill soils being acidic are not suitable for plant growth and traditional shifting cultivation alongwith indiscriminate cutting and burning of forests in every year in ters of timber, fire wood etc. have been affecting seriously the ecological balance of the area. Such practices leave the soil surface barren in addition to loss of fertile top soil surface through erosion. Water holding capacity is also reduced which again affect the availability of water in the lower reaches.

The valley soils are mostly restricted to rice, but these are low in available phosphorous content and susceptible to flood hazards. Due to high clay content in places farming operation becomes very difficult.

To sum up, the soil constraints are:

• Soil acidity

• Low cation exchange capacity

• Soil erosion due to shifting cultivation and deforestation

• Low base status leading to toxicity of Fe and Al.

• Low availability and high phosphate fixation

• High ground waterable and flloding in valley soils.

Potentials : The soils and agroclimate of this hilly region are ideal for the development of horticulture. It is, however, necessary to establish nurseries for varieties specific for the region. It is also possible to exploit these soils for cultivation of tea.

Beels and lakes can be utilised scientifically to expand and improve fish production in the are.

2. Soils of Hot Humid Agro-ecozone with Hyperthermic  Ecosystem

The agro eco-zone encompasses parts of Imphal(Jiribam area) Tamenglong and Churachandpur districts bordering Assam and Mizoram and occupies about 12.8 percent of TGA of the state. This zone experiences  hot summers and cold winters with seasonal dry spells which even extend from November to April. The estimated length of growing period ranges from  270 to 300 days and moisture index ranges from 20-40 petr cent. Mean annual precipitation of Jiribam  station is 2088.7 mm and potential evapotranspiration of 1377.9 mm with an annual average temperature of 24.4^o

The soils of this region are heterogenous in nature and developed in gently sloping narrow valleys and strongly sloping hills with moderate to severe erosion hazards. These soils are in general, well to excessively drained, fine to loamy skeletal and classified as Umbric/Type Dystrochrepts; Typic Udorthents and Typic Haplohumults. These soils are moderately to strongly acidic,  humus rich and have low base saturation. Soils developed in narrow valleys are deep, poorly drained, fine in texture and with  slight erosion hazard.

Land Use

The area is primarily under forest cover, sesamum potato, maize, ginger, tapioca and vegetables are grown under the shifting cultivation system. Horticultural  crops like  Orange, Pineaple, Lemon, Pears etc. are grown in these areas. Narrow valleys are cultivated permanently for Pddy and Maize in general.

Soil Constraints and Potentials

The salient problems and potentials of these soils are :

Constraints : Hill soils of this region are strongly acidic and have low base status and comparatively less moisture holding capacity. these are low in available phosphate contents and highly susceptible to erosion due to heavy and swift runoff over the steeps slopes. Due to shifting cultivation landslides and mass movement are additional man made problems of the region.

 to sum up, these soils suffers from :

• Soil acidity
• Low exchange capacity
• Soil erosion
• Low base status
• Limiting soil depth in steep hill slope and
• Shifting cultivation and landslides

Potentials : The soils of the region being highly acidic and base unsaturated, crops tolerant to acidity will grow effectively under such agroclimate. Horticultural crops like Pineapple, Pears, Peach, Plum, Lemon, Orange and Banana may grow successfully with proper management.

3. Soils of Warm Perhumid Thermic Agro-ecozone

This region comprising the south-western part of the state gradually merging to Mizoram has longest growing period. The land/surface configuration is mostly dissected hills with narrow valley. The region covers 14.4 per cent of the total geagraphical area of the state.The moisture is available through out the year barring some seasonal deficit during November, December and January. The estimated length of growing period varied from 330-365 days.

 The main soil types of this area include Typic/Umbric Dystrochrepts, Typic Haplohumults/Typic Udorthents and Typic Palehumults. The organic carbon content of the soils are high and have low base saturation and low CEC. Soils are highly acidic.

Land Use

The area is under mostly forest, Sesamum, Potato, Maize, Tapioca and vegetables are grown under jhum cultivation. Some areas are used for fruit tree crops. Narrow valleys are generally used for Paddy cultivation.

Soil Constraints and Potential

Constraints : The soils of this agro eco sub-region suffers from

• Soil acidity

• Soil erosion

• Low base status

• Limiting soil depth in steep hill slopes

• Jhum cultivation and land slides

Potentials : Soils of this region being highly acidic and low in base saturation and cation exchange capacity is preferred for crops tolerance to acidity. This region is also suitable for horticultural crops like Pineapple, Pears, Peach, Plum and Banana if planted under little soil and water conservation measures. this region is also favourable for agroforestry and other silvipastural syaystems.

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