Course Content
Crop Production (Unit 6)
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ASRB NET / SRF / Ph.D. Agronomy
Drought in Agriculture
  • Definition: Drought is a prolonged period of below-normal rainfall resulting in moisture stress that adversely affects crop growth, soil fertility, and water availability.
  • Significance: A major constraint in dryland agriculture. Causes yield loss, crop failure, and socio-economic stress.

 

Types of Drought

a) Meteorological Drought

  • Definition: Period when rainfall is significantly below the normal for a region.
  • Cause: Lack of precipitation.
  • Impact: Reduces soil moisture, affects LGS.
  • Example: Arid Rajasthan during a failed monsoon.

 

b) Agricultural Drought

  • Definition: Occurs when soil moisture is insufficient for crop growth, regardless of rainfall.
  • Cause: Rainfall deficit + high evapotranspiration + poor soil moisture retention.
  • Impact: Reduced germination, stunted growth, poor yields.
  • Example: Sorghum crop failing due to mid-season dry spell in semi-arid Deccan Plateau.

 

c) Hydrological Drought

  • Definition: Deficit in surface or groundwater resources (rivers, reservoirs, aquifers).
  • Cause: Prolonged rainfall deficiency affecting rivers, tanks, and groundwater recharge.
  • Impact: Water scarcity for irrigation, drinking, and livestock.

 

d) Socio-Economic Drought

  • Definition: When water shortage affects human activities, including agriculture, livestock, industry, and economy.
  • Cause: Combination of meteorological, agricultural, and hydrological droughts.
  • Impact: Crop failure, livestock loss, reduced income, migration.

 

  1. Drought Syndrome (Crop Response to Drought)

Definition: Drought syndrome refers to the observable symptoms and physiological changes in crops caused by water stress.

Major Symptoms of Drought Stress in Crops

Crop Stage

Symptoms

Germination

Poor or uneven germination, delayed emergence

Vegetative

Wilting, leaf rolling, stunted growth, reduced leaf area

Flowering

Flower drop, delayed flowering, reduced pollen viability

Grain/Pod Filling

Poor grain filling, shriveled grains, low pod set

General

Reduced plant height, yellowing or browning of leaves, early senescence

Physiological Changes in Drought

  1. Reduced turgor pressure → wilting of leaves.
  2. Closure of stomata → reduced photosynthesis.
  3. Increased root-to-shoot ratio → plants try to access deeper soil moisture.
  4. Accumulation of osmolytes (proline, sugars) → protects cells from dehydration.

 

  1. Impact of Drought on Dryland Agriculture
  • Arid regions (<500 mm rainfall): Frequent droughts → crop failure almost every year.
  • Semi-arid regions (500–1000 mm): Occasional mid-season drought → significant yield loss.
  • Dry sub-humid regions (1000–1150 mm): Rare droughts, but still affect sensitive crops.

Facts for ASRB NET:

  • Drought affects ~55% of India’s cultivated area (mostly rainfed).
  • Dryland crops like millets and pulses are more drought-tolerant, but yields are still affected.
  • Early warning systems and drought management strategies are key for sustainable dryland agriculture.

Effect of Drought on Plant Growth and Drought Resistance

 

Effect of Drought on Plant Growth

Drought (water stress) affects plants at morphological, physiological, biochemical, and reproductive levels:

a) Morphological Effects

Plant Part

Effect

Roots

Reduced root growth in shallow soils; sometimes deeper roots develop to access moisture

Shoot

Stunted growth, reduced leaf area, internode shortening

Leaves

Leaf rolling, wilting, early senescence, reduced stomatal area

Flowers/Pods

Flower drop, reduced pod set, poor grain filling

 

b) Physiological Effects

Parameter

Effect

Photosynthesis

Reduced due to stomatal closure and chlorophyll degradation

Transpiration

Decreases initially; severe stress causes wilting

Respiration

Often increases under mild stress; decreases under severe stress

Water Potential

Declines → turgor loss → wilting

Nutrient Uptake

Reduced due to low soil moisture

 

c) Biochemical Effects

  • Accumulation of osmolytes like proline, sugars, and amino acids → maintain cell turgor.
  • Increase in antioxidant enzymes (SOD, catalase, peroxidase) to mitigate oxidative stress.
  • Reduced protein synthesis → affects growth and development.

 

d) Reproductive Effects

  • Delayed flowering or early flowering as survival strategy.
  • Reduced pollen viability → lower fertilization.
  • Poor grain or seed filling → shriveled seeds, low yield.

Fact: In drylands, water stress can reduce yield by 30–70% depending on severity and crop type.

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