Introduction
Dryland agriculture refers to crop production in regions where rainfall is low, erratic, and often insufficient to support intensive irrigated farming. Globally, drylands account for a significant portion of the earth’s land area and support millions of people. In India, a large share of cultivated land falls under rainfed/dryland systems, making these areas vital for food security, employment, and rural livelihoods.
The productivity of dryland areas is primarily governed by soil and climatic conditions, since the absence of assured irrigation makes crops highly dependent on natural rainfall and the soil's ability to store moisture. This document describes the soil types, their properties, and the climatic features typical of dryland regions, focusing on India while drawing global parallels where relevant.
1. Definition of Dryland Areas
Dryland areas are characterized by low and erratic rainfall and a high atmospheric moisture demand. Different institutions use related but distinct thresholds:
- FAO (Food and Agriculture Organization): Areas with a ratio of mean annual precipitation to potential evapotranspiration (P/PET) between 0.05 and 0.65.
- ICAR (India): Regions receiving less than 750 mm annual rainfall are often classified as drylands; regions with 750–1150 mm but without assured irrigation are treated as rainfed.
2. Climatic Conditions of Dryland Areas
2.1 Rainfall Characteristics
Rainfall is the single most crucial climatic factor for dryland agriculture. Key aspects include:
- Low annual rainfall: True drylands typically receive < 750 mm/year. Rainfed zones may receive 750–1150 mm/year.
- Erratic distribution: Rain arrives in a few intense events, often causing runoff and erosion rather than effective soil storage.
- High variability: The coefficient of variation (CV) in annual rainfall in many dryland regions ranges between 20–30%, making rainfall unreliable.
- Seasonality: In India, most rainfall falls during the southwest monsoon (June–September), leading to dry pre- and post-monsoon periods.
Examples (India): Western Rajasthan (~100–400 mm), Central India (Madhya Pradesh, Maharashtra: ~600–1000 mm), Deccan Plateau (~700–900 mm).
2.2 Temperature Regimes
Temperature affects evapotranspiration, soil moisture retention, and crop development:
- Hot summers: Temperatures often reach 40–48°C (May–June) in semi-arid zones.
- Mild/cool winters: Night temperatures may drop to 5–8°C in some north-western drylands.
- Diurnal and seasonal variation: Large swings in day–night and seasonal temperatures are common.
Such extremes favor drought-resistant crops (e.g., sorghum, pearl millet, groundnut, pulses).
2.3 Relative Humidity and Evapotranspiration
Key aspects include:
- Relative humidity (RH): Generally low (≈ 20–40%) in hot dry zones.
- Potential evapotranspiration (PET): Often several times greater than rainfall. In some arid zones PET can exceed rainfall by 3–5 times.
- Moisture deficit: Large deficits between precipitation and atmospheric demand make soil moisture the limiting factor.
2.4 Length of Growing Period (LGP)
The Length of Growing Period (LGP) measures the time during which rainfall and stored soil moisture are sufficient for crop growth:
- Arid regions: LGP < 75 days
- Semi-arid regions: LGP 75–120 days
- Dry sub-humid regions: LGP 120–180 days
LGP determines whether single-season cropping (kharif only) or multiple seasons (kharif + rabi) are feasible.
2.5 Climatic Hazards
- Drought — meteorological, agricultural and hydrological droughts are common.
- Flash floods and waterlogging — intense rainfall events can cause short-duration floods.
- Heat and cold waves — damaging during sensitive crop stages (e.g., flowering).
- Wind erosion — especially on sandy soils.
3. Soil Conditions of Dryland Areas
Soils in dryland regions vary from sandy desert soils to deep clays. Their physical and chemical properties largely determine how much rainfall can be stored and made available to crops.
3.1 General Characteristics
- Low organic matter: Biomass returns are low and decomposition rates high, reducing soil carbon stocks.
- Poor fertility: Deficiencies in N, P and sometimes K and micronutrients are common.
- Variable depth: Ranging from very shallow to very deep; depth affects water-storage capacity.
- Surface crusting and hardpans: Reduce infiltration and seedling emergence.
- Erosion-prone: Both wind and water erosion degrade soils.
3.2 Major Soil Types in Indian Drylands
(a) Alfisols (Red Soils)
Distribution: Eastern Karnataka, Tamil Nadu, parts of Andhra Pradesh.
Properties: Shallow to moderately deep, low water-holding capacity (WHC), well-drained, low in nitrogen and phosphorus.
Common crops: Groundnut, sorghum, finger millet.
(b) Vertisols (Black Soils)
Distribution: Maharashtra, Madhya Pradesh, parts of Andhra Pradesh and Karnataka.
Properties: Deep clayey soils high in montmorillonite, high WHC (150–200 mm per metre of profile), crack in summer and swell in rainy season. Chemically rich in bases but often low in N and P.
Common crops: Cotton, sorghum, soybean, pigeon pea.
(c) Aridisols (Desert Soils)
Distribution: Western Rajasthan, parts of Gujarat.
Properties: Sandy to sandy loam texture, very low organic matter, high infiltration but very low moisture retention. Salinity and alkalinity are common in some tracts.
Common crops: Pearl millet, cluster bean (guar), moth bean.
(d) Entisols and Inceptisols
Distribution: Recent alluvial soils in parts of Uttar Pradesh, Bihar and other plains.
Properties: Moderately fertile but can be moisture-limited under erratic rainfall.
Common crops: Maize, wheat and pulses under rainfed conditions.
3.3 Soil Moisture Availability
The effectiveness of rainfall is strongly influenced by soil texture and structure:
- Water-holding capacity (WHC): Sandy soils may store <50 mm of plant-available water in the root-zone, whereas deep vertisols may store >200 mm.
- Infiltration vs storage: Sandy soils have high infiltration rates but low storage, while fine-textured clays have slower infiltration but higher storage potential.
- Evaporation losses: Bare soils lose more moisture; mulches reduce evaporation.
For instance, vertisols can often sustain a rabi crop on stored monsoon moisture while alfisols and sands cannot.
3.4 Soil Fertility Issues
- Macronutrient deficiencies: Nitrogen is commonly deficient; phosphorus is often low in red soils; potassium can be limiting in lateritic soils.
- Micronutrients: Zinc and iron deficiencies occur frequently; boron deficiency appears in some eastern tracts.
- Low soil organic matter: Typically <0.5% in many dryland fields, reducing aggregate stability and microbial activity.
3.5 Soil Degradation Mechanisms
- Water erosion: Sheet and gully erosion on sloping alfisols and lateritic tracts.
- Wind erosion: Severe in arid and semi-arid sandy zones (e.g., western Rajasthan).
- Salinization and alkalinity: In low-rainfall irrigated and poorly-drained areas.
- Nutrient mining: Continuous cultivation without replenishment of nutrients.
4. Regional Overview — Soils and Climate in Indian Drylands
| Region | Rainfall (mm) | Major Soils | Typical Crops | Key Issues |
|---|---|---|---|---|
| Western Rajasthan | 100–400 | Sandy, Aridisols | Pearl millet, guar, moth bean | Drought, wind erosion |
| Central Plateau (MP, MH) | 600–1000 | Vertisols (black soils) | Cotton, soybean, sorghum, pigeon pea | Cracking, seasonal waterlogging |
| Deccan Plateau (AP, KA) | 600–900 | Alfisols, Vertisols | Groundnut, ragi, sorghum | Low fertility, erosion |
| Eastern plains (Bihar, UP) | 800–1200 | Inceptisols, Entisols | Maize, wheat, pulses (rainfed) | Floods and droughts (variable) |
| Tamil Nadu (dry tracts) | 400–800 | Alfisols | Groundnut, pearl millet, pulses | Erratic monsoon, moisture stress |
5. Interaction of Soil and Climate in Drylands
Productivity in drylands results from the interaction between soil and climate rather than from either factor alone. Examples:
- Low rainfall + sandy soils: Extremely drought-prone (e.g., western Rajasthan).
- Moderate rainfall + vertisols: Potential for residual-moisture cropping and limited rabi crops (e.g., parts of Maharashtra, MP).
- Higher rainfall but poor soils: Nutrient limitations, runoff and erosion reduce productive potential (e.g., parts of eastern India).
Therefore, land management interventions (contour farming, mulching, bunding, drought-tolerant varieties, integrated nutrient management) must be adapted to both soil type and climate.
6. Case Studies
Case 1: Pearl Millet in Western Rajasthan
Rainfall: ~300 mm; Soil: Sandy with very low WHC. Strategies: Short-duration pearl millet varieties, low plant density, intercropping with legumes (e.g., moth bean), and soil moisture conservation with mulches and contour bunds.
Case 2: Cotton on Vertisols (Maharashtra)
Rainfall: 700–900 mm; Soil: Deep black soils storing >200 mm root-zone water. Strategies: Timely sowing with onset of monsoon, use of stored moisture to support rabi chickpea, and careful management of waterlogging and cracking.
Case 3: Groundnut in Alfisols (Anantapur, Andhra Pradesh)
Rainfall: 550–650 mm; Soil: Shallow red soils low in fertility. Strategies: Rainwater harvesting (farm ponds), gypsum application, integrated nutrient management, and intercropping with pigeon pea to improve soil cover and nitrogen economy.
7. Implications for Crop Planning and Management
- Crop selection: Choose crops suited to local LGP, soil depth and WHC — pearl millet, sorghum, pulses, groundnut, and minor millets are well-adapted.
- Cropping systems: Mixed cropping and intercropping spread risk and improve resilience.
- Soil & water conservation: Contour bunds, graded bunds, retention structures, farm ponds and mulching improve moisture use efficiency.
- Nutrient management: Integrated nutrient management with chemical fertilizers, organic manures and biofertilizers addresses deficiencies and builds soil health.
- Varietal choices: Short-duration and drought-tolerant cultivars reduce risk.
Conclusion
Dryland soils and climates are characterized by low and erratic rainfall, high evapotranspiration, temperature extremes, and soils with low organic matter and limited fertility. Nevertheless, these regions are essential for national and local food systems. Understanding the combined effects of climate and soil on water availability and nutrient supply is critical for effective crop planning, conservation practices, and resilient farming systems. With appropriate management — soil and water conservation, improved varieties, and integrated nutrient management — dryland areas can sustainably support livelihoods and contribute significantly to food security.
