Agro-Climatic Zones in Assam
Introduction
Definition of Agro-Climatic Zones
- An Agro-Climatic Zone (ACZ) refers to a geographically defined area characterized by:
- Similar climatic conditions (temperature, rainfall, humidity)
- Distinct soil types and topography
- Specific cropping patterns and farming systems
- These zones help in scientific planning of agriculture by optimizing resource utilization and enhancing crop productivity.
Importance of Agro-Climatic Zoning
A. Agricultural Benefits
- Crop Suitability – Helps in selecting the most suitable crops for a region.
- Efficient Resource Use – Assists in optimal utilization of land, water, and inputs like fertilizers and pesticides.
- Sustainable Agriculture – Prevents land degradation and ensures long-term agricultural sustainability.
B. Economic & Policy Implications
- Improved Productivity – Enhances farm output by aligning practices with climatic conditions.
- Better Policy Formulation – Governments use agro-climatic data to design region-specific agricultural policies.
- Investment in Infrastructure – Helps in planning irrigation projects, storage facilities, and market linkages.
C. Climate Adaptation & Risk Management
- Disaster Preparedness – Aids in managing floods, droughts, and soil erosion.
- Climate Resilience – Encourages adoption of climate-resilient crops and farming methods.
- Pest & Disease Control – Facilitates early warning systems and preventive measures.
Basis of Agro-Climatic Classification
Agro-climatic zones are classified based on multiple parameters. The key factors are:
Criteria | Description |
Climatic Factors | Rainfall, temperature, humidity, evapotranspiration |
Soil Characteristics | Soil type, fertility, moisture-holding capacity |
Topography | Altitude, slope, drainage patterns |
Hydrological Features | River systems, groundwater levels, irrigation potential |
Vegetation & Land Use | Natural vegetation, dominant cropping pattern |
This classification provides a scientific approach to regional agricultural planning and ensures efficient land-use management.
Easy Way to Understand Agro-climatic zones :
Think about different places around you:
Rainfall : Some places get a lot of rain
Soil : Some places have dry or sandy soil
Temperature : Some areas are hot, some are cool
Topography : Some land is flat, while others are hilly
Because of all these above differences:
Rice grows well where there is plenty of water
Tea grows best in rainy and slightly hilly areas
Maize, vegetables, and fruits grow better in drier or hilly regions.
- Special flood-tolerant crops can grow better along Flood prone areas.
Agro-Climatic Classification of Assam
Concept of Agro-Climatic Zoning in India (Planning Commission’s Classification)
The Planning Commission of India (1988) classified the country into 15 Agro-Climatic Regions (ACRs) based on soil type, climate, rainfall, and topography. These regions were identified to optimize resource utilization and agricultural planning at the national level.
Assam falls under the Eastern Himalayan Region, which is characterized by high rainfall, diverse soil types, and a humid subtropical climate. This region is suitable for crops like rice, tea, jute, and horticultural crops.
The classification helps in:
- Scientific allocation of resources for agriculture and irrigation.
- Promoting region-specific crops and farming systems.
- Developing strategies to combat climate-related challenges like floods and soil erosion.
Assam’s Position in National Agro-Climatic Zoning
In the national framework, Assam is placed under the Eastern Himalayan Region, but due to its diverse topography, rainfall, and soil composition, a more detailed classification is required. The state exhibits multiple microclimatic variations that impact agricultural productivity.
Key features of Assam’s agro-climatic conditions:
- High Rainfall: Annual precipitation ranges from 1,500 mm to over 3,000 mm, making it one of the wettest regions in India.
- Temperature Variations: Mean annual temperature varies between 18°C and 27°C.
- Soil Diversity: Alluvial, lateritic, and red soils influence crop choices.
- Flood & Erosion Prone Areas: The Brahmaputra and Barak river basins are highly affected by floods, requiring adaptive agricultural practices.
Classification by Assam Agriculture Department
To better suit Assam’s diverse agricultural landscape, the Assam Agriculture Department classified the state into 6 Agro-Climatic Zones based on rainfall, soil type, topography, and cropping patterns.
Agro-Climatic Zone | Key Features | Major Crops |
North Bank Plain Zone | Alluvial soil, high flood risk | Rice, mustard, pulses |
Upper Brahmaputra Valley Zone | Fertile alluvial soil, moderate rainfall | Tea, rice, jute, sugarcane |
Central Brahmaputra Valley Zone | Well-drained soil, mixed cropping | Rice, vegetables, oilseeds |
Lower Brahmaputra Valley Zone | Heavy rainfall, flood-prone | Jute, rice, mustard, pulses |
Barak Valley Zone | High humidity, lateritic soil | Areca nut, betel leaf, vegetables |
Hills Zone | Acidic soil, suitable for horticulture | Pineapple, oranges, ginger |
Factors Influencing Agro-Climatic Zones in Assam
Climatic Factors
Climate plays a crucial role in defining the agro-climatic zones of Assam, influencing crop selection, productivity, and farming techniques.
Rainfall Pattern
Assam receives high rainfall due to its proximity to the Bay of Bengal and the Himalayas. Annual rainfall varies from 1,500 mm to 3,800 mm, with the heaviest precipitation occurring during the monsoon season (June–September). Excess rainfall leads to floods, while inadequate rainfall in some areas causes drought-like conditions.
Temperature Variability
The state experiences sub-tropical to humid climatic conditions, with temperature variations across different regions.
- Summer (March–June): Maximum temperature can rise up to 35°C.
- Winter (December–February): Minimum temperature can drop to 5°C in hilly areas.
- Temperature influences cropping patterns, with rice, tea, and pulses growing well in warmer plains, while horticultural crops thrive in cooler hill regions.
Humidity & Evapotranspiration
Assam has high humidity levels, ranging from 60% to 90%, which affects crop growth and pest infestations. High evapotranspiration in dry months increases irrigation requirements.
Seasonal Variations
Agricultural activities are divided into three main cropping seasons:
- Kharif (June–October): Rice, jute, pulses, and oilseeds dominate during the monsoon.
- Rabi (November–March): Wheat, mustard, lentils, and vegetables thrive in cooler months.
- Zaid (April–May): Short-duration crops like cucumbers, melons, and fodder are grown.
Physiographic Factors
Assam’s diverse topography impacts soil fertility, drainage, and agricultural practices.
Relief Features (Hills, Plains, Floodplains)
Physiographic Region | Characteristics | Agricultural Suitability |
Hills (Karbi Anglong, Dima Hasao) | Undulating terrain, acidic soil | Horticulture (pineapple, orange, ginger) |
Plains (Brahmaputra & Barak Valley) | Fertile alluvial soil, prone to floods | Paddy, jute, pulses |
Floodplains (Near Brahmaputra & its tributaries) | Prone to seasonal floods & silt deposition | Seasonal cropping, flood-resistant varieties |
Soil Types & Fertility
The state has four major soil types that determine agricultural productivity.
- Alluvial Soil: Found in river valleys, highly fertile, supports rice and jute cultivation.
- Lateritic Soil: Common in highlands, acidic in nature, suitable for tea and horticulture.
- Red Soil: Found in hill regions, less fertile, requires fertilizers for better yield.
- Sandy & Clayey Soil: Present in flood-prone areas, used for mixed cropping.
Hydrological Factors
Water availability, both surface and groundwater, affects agricultural sustainability in Assam.
River Systems & Flooding
The Brahmaputra and Barak rivers, along with their tributaries, shape the hydrology of Assam.
- Brahmaputra River Basin: Prone to annual floods, leading to crop damage but also soil enrichment through sediment deposition.
- Barak River Basin: Supports agriculture in southern Assam, providing irrigation for multiple crops.
- Tributaries (Subansiri, Dhansiri, Manas, Kopili, etc.): Play a vital role in localized irrigation.
Groundwater Availability
Groundwater levels vary across different zones. The Brahmaputra Valley has high groundwater recharge potential, while hilly areas face limited groundwater availability, requiring rainwater harvesting and efficient irrigation techniques.
Irrigation Potential
Despite high rainfall, irrigation facilities are crucial for agriculture during dry months.
Irrigation Source | Usage & Benefits |
Canal Irrigation | Used in low-lying plains for paddy cultivation |
Tube Wells & Dug Wells | Supplementary irrigation in drier months |
Rainwater Harvesting | Essential for hilly regions with less groundwater |
Pond & Tank Irrigation | Supports fisheries and small-scale irrigation |
Vegetation & Land Use Patterns
The vegetation of Assam is influenced by climatic and physiographic factors, leading to different land use patterns.
- Forested Areas: Occupy about 35% of the land, primarily in hilly regions, supporting biodiversity.
- Agricultural Land: Covers the Brahmaputra & Barak Valleys, where rice, tea, and oilseeds are dominant.
- Grasslands & Wetlands: Support fisheries, livestock grazing, and seasonal cropping in flood-prone zones.
Understanding these factors is essential for agricultural planning, climate resilience, and sustainable farming in Assam.
1. North Bank Plain Zone (NBPZ)
Location
Lies north of the Brahmaputra River (Hence, North Bank), characterized by floodplains, alluvial deposits, and moderate elevation.
Includes 7 districts like Dhemaji, Lakhimpur,Majuli, Biswanath, Sonitpur, Udalguri and Darrang.
Covers 18.37% of state’s area
Climatic characteristics
Humid subtropical climate.
High Humidity (73%–90%, peaking inmonsoon), influencing crop growth and pest infestations.
Annual rainfall: 2500–3000 mm (varies regionwise)
Rainfall Distribution: Erratic pattern → pre-monsoon showers, intense monsoon (Heavy SW monsoon (June–September)), low post-monsoon/winter rain.
Temperature: Sub-tropical; hot humid summers (max 30–32°C), mild winters (min 10–15°C)
Frequent floods and riverbank erosion
Soil & Topography
Topography: Mostly plain/alluvial plains with regional variations;
Foothills in north (gentle slopes) – Tea cultivation
Central region – old alluvium belt.
Low-lying riverine areas near Brahmaputra (floodplains) – new alluvial soils
- Soils: Predominantly new and old alluvial (fertile); variations include:
- Clay and clay loam (high organic matter, good water/nutrient retention; medium N, P, K).
- Alluvial (medium fertility).
- Sandy loam/sandy in patches (low organic matter, low NPK).
- Soil fertility: Medium to high in lowlands; acidic tendencies in some areas.
- Issues: Flood-prone lowlands, erosion in foothills, sand casting post-floods.
Major Crops
- Dominant Crop: Paddy/rice (60–70% of cropped area); sali (winter rice) dominant; autumn (ahu), summer (boro) also grown.
- Other Field Crops: Jute, potato, pulses (black gram), oilseeds (rapeseed-mustard), maize.
- Horticulture: Wide potential due to diverse conditions; banana, Assam lemon, pineapple, citrus, vegetables, tuber crops, spices (ginger, turmeric, chilli, garlic), plantation crops (coconut, arecanut, betel vine).
- Allied Activities: Piggery, poultry, goat rearing, fishery, sericulture.
- Cropping Intensity: Moderate (e.g., ~144% in Dhemaji); mostly rainfed.
Major Farming Systems and Constraints
- Major Systems:
- Dominant – Rice-based (mono-cropping),
- Plains – rice + pulses/oilseeds,
- Uplands – horticulture + plantation ,
- Most common – integrated farming (crops + livestock + fishery).
- Constraints:
- Frequent flash floods (from Arunachal streams) and seasonal droughts.
- Erratic monsoon → 40% probability of adverse crop production.
- Low irrigation (~6–7% in some districts); high rainfed dependence.
- Resource-poor farmers; limited mechanization; shifting cultivation fringes.
- Pests/diseases (e.g., stem borer, leaf folder, blast in rice)
- Soil erosion – along riverbanks.
- Vulnerabilities: Climate change → increased flash floods, droughts; makes rainfed agriculture risky/unprofitable.
- Major Systems:
2. Upper Brahmaputra Valley Zone (UBVZ)
Location :
- Covers the upper (eastern) reaches of the Brahmaputra Valley (along the southern bank of river Brahmputra).
- 6 Districts: Golaghat, Jorhat, Sivasagar, Charaideo, Dibrugarh, Tinsukia.
- Covers 20.40% of state’s area
- Terrain: Mostly flat to moderately undulating alluvial plains; gentle slopes; some char (riverine) lands; tea garden uplands in foothills.
Climatic Characteristics
- Annual Rainfall: High; 2000–3500 mm (e.g., ~2400 mm in Charaideo/Sivasagar, 2600–3200 mm in parts of Dhemaji fringes, average ~2295–3000 mm across zone).
- Rainfall Distribution: Heavy SW monsoon (June–September); pre-monsoon showers; relatively lower post-monsoon/winter rain; erratic pattern in some years.
- Temperature: Sub-tropical humid; hot summers (max 30–35°C), mild winters (min 9–15°C).
- Relative Humidity: High (especially monsoon); supports lush vegetation and tea estates.
- Key Features: Flood-prone due to Brahmaputra and tributaries (e.g., Burhi Dihing, Dikhow); occasional flash floods; suitable for rainfed + irrigated cropping (mostly rainfed).
Soil Types and Topography
- Topography: Predominantly flat alluvial plains; moderately undulating in parts; char lands (river islands) with variable stability.
- Soils: Rich alluvial soils (new and old); highly fertile due to annual silt deposition; deep to moderately deep loamy to clay loam.
- Characteristics: High organic matter, nitrogen-rich; good phosphoric content; slightly acidic to neutral in uplands.
- Variations: Sandy loam in patches; red loamy in some elevated areas; laterite fringes.
- Soil fertility: Excellent for rice, tea, and plantation crops; flood replenishment enhances productivity.
- Issues: Soil acidity in tea estates (managed with lime); sand casting in chars; erosion in unstable riverine areas.
Major Crops and Cropping Patterns
- Dominant Crop: Paddy/rice (sali/winter rice major; also autumn/ahu and summer/boro); covers large area.
- Plantation Crops: Tea (world-famous Assam tea; major economic driver in Dibrugarh, Tinsukia, Jorhat, Sivasagar); arecanut, coconut, rubber in parts.
- Other Field Crops: Black gram (pulses), oilseeds (rapeseed-mustard), jute (limited), maize.
- Horticulture: Banana, orange, pineapple, papaya, vegetables; spices (ginger, turmeric, chilli).
- Cropping Intensity: Moderate to high in stable areas; rainfed dominant but irrigation supports boro rice.
- Special: Tea estates dominate landscape; integrated systems (tea + shade crops); potential for off-season vegetables.
Major Farming Systems and Constraints
- Major Systems: Rice-based mono-cropping; rice + pulses/oilseeds; tea plantation dominant; horticulture + plantation in uplands; integrated (crops + livestock + fishery in chars).
- Constraints:
- Annual flooding and river erosion (Brahmaputra chars unstable → low crop cultivation in large islands).
- High rainfed dependence; erratic monsoon affects rainfed planning.
- Pests/diseases in rice (blast, stem borer) and tea (red spider mite, blister blight).
- Soil management in acidic tea soils; low mechanization in smallholdings.
- Climate vulnerabilities: Increasing drought trends in some analyses; flood-drought alternation.
- Vulnerabilities: Most vulnerable to climate change among some zones (declining SPI/SPEI trends); flood risks high.
3. Central Brahmaputra Valley Zone (CBVZ)
Location :
- Covers the central plains of the Brahmaputra Valley.
- 3 Districts: Nagaon, Hojai, Morigaon.
- Covers 7% of state’s area
- Terrain: Vast plainlands dotted with fewer hilly terrains; alluvial floodplains; some char (riverine) areas; gentle slopes.
Climatic Characteristics
- Annual Rainfall: Moderate to moderate-high; ~1800–2500 mm (e.g., Nagaon ~1880 mm, Morigaon ~1245–1880 mm range; some sources average around 2000 mm).
- Rainfall Distribution: SW monsoon dominant (June–September); pre-monsoon showers; relatively balanced but with pockets of erratic patterns leading to occasional droughts in uplands.
- Temperature: Sub-tropical humid; hot summers (max 30–35°C), mild winters (min 10–20°C); supports double/triple cropping in irrigated areas.
- Relative Humidity: High during monsoon; conducive to rice and vegetable growth.
- Key Features: Lower drought risk ; flood-prone in lowlands but less severe than Lower Brahmaputra Valley; some rain-shadow effects in uplands.
Soil Types and Topography
- Topography: Mostly flat to gently undulating alluvial plains; vast open lands suitable for mechanization; fewer hills compared to northern/southern zones.
- Soils: Predominantly fertile alluvial (new and old); deep loamy to clay loam; high organic matter from Brahmaputra silt deposition.
- Characteristics: Good nutrient retention (medium to high N, P, K); slightly acidic in parts; excellent for rabi crops in floodplains.
- Variations: Clay loam dominant; sandy loam in patches; fertile char soils for pulses/oilseeds.
- Soil fertility: High; supports diverse cropping; annual flooding replenishes nutrients.
- Issues: Waterlogging in lowlands; soil erosion in unstable riverine areas; occasional sand casting post-floods.
Major Crops and Cropping Patterns
- Dominant Crop: Paddy/rice (sali/winter rice major; ahu/autumn and boro/summer also significant); covers large portion of cropped area.
- Other Field Crops: Pulses (black gram, green gram – major contribution to state’s pulses), oilseeds (rapeseed-mustard), jute, maize, sugarcane.
- Horticulture: Banana, papaya, pineapple, citrus, vegetables (winter vegetables prominent); spices (ginger, turmeric, chilli).
- Cropping Intensity: Moderate to high; potential for rabi/summer intensification due to fertile soils and irrigation scope.
- Special: Pulse production significant; opportunities for fallow season utilization (e.g., rabi crops post-kharif rice); millet trends in some studies.
Major Farming Systems and Constraints
- Major Systems: Rice-based (mono-cropping common); rice + pulses/oilseeds (rabi); integrated systems (crops + livestock + fishery); horticulture in uplands.
- Constraints:
- Floods in lowlands + seasonal droughts in uplands (erratic rainfall).
- Low irrigation coverage in rainfed areas; dependence on monsoon.
- Pests/diseases in rice and pulses; storage issues for pulses.
- Resource limitations for small farmers; low mechanization.
- Climate change: Alternating flood-drought; moderate vulnerability but lower than UBV/NBP.
- Vulnerabilities: Erratic monsoon impacts rainfed productivity; need for better moisture management.
4. Lower Brahmaputra Valley Zone (LBVZ)
Location
- Covers the lower (western) reaches of the Brahmaputra Valley.
- 13 Districts: Goalpara, Bongaigaon, Barpeta,Bajali, Kamrup, Kamrup(M), Nalbari, Baksa, Chirang, Tamulpur Dhubri, South Salmara-Mankachar, Kokrajhar.
- Covers 25.75% of state’s area
- Terrain: Flat alluvial plains; extensive char (riverine islands); gentle southward slope; low-lying floodplains; some hilly fringes in north (e.g., Chirang, Baksa).
Climatic Characteristics
- Annual Rainfall: Very high; 2000–4000+ mm (e.g., Baksa ~3575 mm, Dhubri ~3264 mm, Bongaigaon ~3219 mm, Barpeta ~2287 mm; average zone ~2500–3500 mm).
- Rainfall Distribution: Intense SW monsoon (June–September); heavy pre-monsoon; high rainy days (120–140+); contributes to severe flooding.
- Temperature: Sub-tropical humid; hot summers (max 30–35°C), mild winters (min 10–20°C).
- Relative Humidity: Very high (especially monsoon); supports dense vegetation but exacerbates waterlogging.
- Key Features: Severe annual floods (Brahmaputra + tributaries like Manas, Pagladiya); flash floods; lower drought risk (SGI decreasing but overall low vulnerability per studies); high moisture but erratic intensity.
Soil Types and Topography
- Topography: Mostly flat alluvial plains; extensive char lands (unstable, seasonal); low-lying with poor drainage; gentle slopes southward.
- Soils: Predominantly deep new alluvial (fertile from Brahmaputra silt); loamy to clay loam/silty loam; high organic matter.
- Characteristics: Good nutrient status (medium N, P, K); slightly acidic to neutral; excellent water retention but prone to waterlogging.
- Variations: Sandy loam in chars; silty in floodplains.
- Soil fertility: High; annual silt deposition boosts productivity.
- Issues: Severe erosion/sand casting in chars; waterlogging/acidity in lowlands; flooding damages soil structure.
Major Crops and Cropping Patterns
- Dominant Crop: Paddy/rice (sali/winter rice major; ahu/autumn, boro/summer also grown); covers large cropped area; flood-tolerant varieties essential.
- Other Field Crops: Jute (significant in western districts), pulses (black gram), oilseeds (rapeseed-mustard), maize, groundnut.
- Horticulture: Pineapple, banana, betel nut, vegetables; spices (chilli, ginger limited).
- Cropping Intensity: Moderate; rainfed dominant; potential for rabi in better-drained areas.
- Special: Char cultivation (pulses, oilseeds, vegetables on stable chars); jute prominent; betel nut/arecanut in pockets.
Major Farming Systems and Constraints
- Major Systems: Rice-based mono-cropping; rice + jute/pulses; integrated (crops + fishery in chars/lowlands); horticulture in uplands, intensive cultivation in densely populated regions.
- Constraints:
- Severe annual floods/erosion (60%+ area vulnerable); char instability limits permanent cropping.
- High rainfed dependence; waterlogging delays sowing/harvesting.
- Pests/diseases (e.g., higher fungal incidence like blast in humid conditions).
- Low irrigation; soil degradation from sand casting.
- Climate vulnerabilities: High flood risk; moderate drought pockets; increasing erratic rainfall.
- Vulnerabilities: Among highest flood-prone zones; climate change intensifies flooding.
5. Hill Zone
Location
- Covers the hill districts and plateaus in southern/central Assam.
- 3 Districts: Karbi Anglong, West Karbi Anglong, Dima Hasao (formerly North Cachar Hills).
- Covers 19.50% of state’s area
- Terrain: Steep hills, plateaus (e.g., Karbi Anglong plateau/Mikir Hills), valleys; elevations 150–1,360+ m; rugged with dense forests.
Climatic Characteristics
- Annual Rainfall: High; >3000 mm in many areas (e.g., ~2416 mm average in Karbi Anglong plateau; influenced by SW monsoon and orographic effects).
- Rainfall Distribution: Heavy SW monsoon (June–September); intense rains leading to runoff; drier winter/post-monsoon periods.
- Temperature: Sub-tropical to temperate in higher elevations; cooler than plains (salubrious climate); summers warm-humid, winters mild-cool.
- Relative Humidity: High; supports lush vegetation.
- Key Features: Frequent landslides; high humidity; moderate drought trends ; climate salubrious compared to humid plains.
Soil Types and Topography
- Topography: Steep slopes, hills, plateaus; high erosion risk; undulating with valleys.
- Soils: Predominantly red, yellow, reddish-brown, lateritic (uplands); acidic (pH often higher/less acidic than plains in some reports, but generally acidic 4.5–5.8 range); low to medium fertility.
- Characteristics: Medium P₂O₅ status (better than some plain zones); low N, K in patches; prone to erosion and nutrient leaching on slopes.
- Variations: Red loamy in hills; less fertile than alluvial plains.
- Soil fertility: Moderate; requires organic amendments; shifting cultivation depletes fertility over cycles.
- Issues: Severe soil erosion; acidity; low nutrient retention on slopes; aluminum toxicity sporadic.
Major Crops and Cropping Patterns
- Dominant Crop: Upland rice (direct-seeded/jhum rice); maize.
- Other Field Crops: Potato, hill sesame (Sesamum indicum), pulses, oilseeds; ginger, turmeric (spices prominent).
- Horticulture: Pineapple, orange, passion fruit, banana, papaya, litchi; plantation crops (tea, rubber in suitable pockets).
- Cropping Intensity: Low to moderate; jhum dominant (shifting cultivation with long fallows 2–10+ years).
- Special: Jhum/agroforestry systems (crops + trees like tree bean, orange, banana in fallows); market-oriented spices/horticulture emerging.
Major Farming Systems and Constraints
- Major Systems: Shifting cultivation (jhum) dominant (rice + maize + vegetables + fallow regeneration); agroforestry; settled horticulture/plantation in valleys; integrated (crops + livestock like hill goats, piggery + fishery limited).
- Constraints:
- Steep slopes → severe soil erosion and landslides.
- Shifting cultivation → fertility decline, deforestation, biodiversity loss; shortening fallow cycles due to population pressure.
- Low irrigation; rainfed dependence; poor market access in remote hills.
- Pests/diseases in humid conditions; wildlife damage.
- Climate vulnerabilities: Declining rainfall trends (moderate drought risk); increasing landslides; climate change impacts on jhum.
- Vulnerabilities: High erosion; moderate drought risk (HR category in studies); transition from jhum challenging.
6. Barak Valley Zone (BVZ)
Location
- Covers the Barak Valley region in southern Assam.
- 3 Districts: Cachar, Sribhumi, Hailakandi.
- Covers 8.9% of state’s area
- Terrain: Fertile plains along Barak River and tributaries; low-lying areas; some undulating/hilly fringes (e.g., southern parts); riverine floodplains.
Climatic Characteristics
- Annual Rainfall: Very high; 2500–4000+ mm (e.g., Cachar ~3020 mm with 146 rainy days; Karimganj ~4073 mm average; Hailakandi ~2500+ mm; zone overall 3000–4000 mm).
- Rainfall Distribution: Intense SW monsoon (June–September); heavy pre-monsoon; high rainy days (120–150+); short concentrated rainy period interspersed with dry spells.
- Temperature: Sub-tropical warm-humid; hot summers (max 30–35°C), mild winters (min 10–20°C); high humidity year-round.
- Relative Humidity: Very high; influenced by Bay of Bengal moisture-laden winds.
- Key Features: Flash floods common (e.g., major floods in 1986, 1991, 2004); high moisture favours pests/diseases; low drought risk.
Soil Types and Topography
- Topography: Mostly flat to gently undulating plains; fertile along Barak River; some hilly/undulating in fringes.
- Soils: Mix of red lateritic (uplands/hills) and alluvial (plains/riverine); sandy loam to silty loam/clay.
- Characteristics: Acidic (pH 4.6–5.7, often 4.9–5.3); medium fertility; good for rice/horticulture with amendments.
- Variations: Alluvial in lowlands (fertile, nutrient-rich); lateritic in uplands (less fertile, needs lime/organic matter).
- Soil fertility: Moderate to high in plains; acidity limits some crops (requires amendments like lime).
- Issues: Acidity; waterlogging in lowlands; erosion in hilly fringes; flood damage.
Major Crops and Cropping Patterns
- Dominant Crop: Paddy/rice (sali/winter rice major; ahu/autumn, boro/summer); flood-tolerant varieties common.
- Plantation Crops: Tea (significant); betel vine (paan), arecanut, coconut.
- Other Field Crops: Pulses (rajmah, black gram), oilseeds, jute (limited), vegetables.
- Horticulture: Pineapple, banana, citrus (orange), papaya, vegetables; spices (chilli, ginger, turmeric).
- Cropping Intensity: Moderate; rainfed dominant; potential for double cropping in medium lands.
- Special: Betel vine prominent; green manuring (e.g., dhaincha before sali rice); shifting cultivation (jhum) in hilly fringes (fallow 2–10 years; species like orange, banana, betel leaf, tree bean in fallows).
Major Farming Systems and Constraints
- Major Systems: Rice-based mono-cropping; rice + pulses/vegetables; tea/betel vine plantation; integrated (crops + horticulture + livestock); shifting cultivation in forest villages/hilly parts (transitioning to agroforestry/commercial fallow use).
- Constraints:
- Flash floods/waterlogging; high humidity → pests/diseases (e.g., blast, sheath blight in rice).
- Acidic soils requiring amendments; low mechanization.
- Rainfed dependence; erratic intense rainfall.
- Shifting cultivation pressure on forests; weed infestation/fertility loss in jhum.
- Climate vulnerabilities: high flood risk.
- Vulnerabilities: High flood proneness; moderate climate change impacts (reduced rainfall trends).
Why Agro-Climatic Zoning is Useful :
Agro-climatic zoning helps:
- Helps in crop selection and diversification
Reduce crop failure
Use water, fertilizer, and land properly to its optimum capacity.
Increase farm production and income
Improves soil and water management
Assists in agricultural planning and research
Reduces risks from floods and climate variability
PYQs
2018:
- What is an Agro Climatic Zone? Describe the Agroclimatic Zones of Assam?
2023:
Which of the following names of the Agroclimatic Zones of Assam is/are not correct?
(i) Upper Brahmaputra Valley
(ii) North Central Brahmaputra Valley
(iii) Barail Zone
(iv) Hill Zone
Select the correct answer using the codes given below.
(A) (i) only
(B) (iii) and (iv) only
(C) (ii) only
(D) (ii) and (iii) only
Let us know any further suggestions ,we at sudurbhai.com will be happy to hear from you in our comment section below !