Growth and Development of Crops

Introduction

• Growth and development are two fundamental physiological processes that determine the life cycle, productivity, and yield of a crop plant.
  These processes involve cell division, cell enlargement, differentiation, and morphogenesis, which ultimately result in the formation of roots, stems, leaves, flowers, fruits, and seeds.
• Understanding how plants grow and develop is essential for crop management — helping farmers and agronomists optimize environmental and agronomic factors such as water, nutrients, light, and temperature to maximize productivity.

Definition and Meaning

Growth

• Growth is defined as a permanent, irreversible, and quantitative increase in size, weight, volume, or number of cells in an organism.
• According to Leopold (1958): “Growth is an irreversible increase in size, volume, or weight of a living organism, usually accompanied by an increase in dry matter.”

Key Characteristics of Growth:

• It is irreversible (once occurred, cannot be undone).
• It is quantitative (measurable).
• It involves cell division and cell elongation.
• It depends on metabolic processes and environmental conditions.

Growth can be measured in terms of:

• Increase in biomass (dry matter)
• Increase in height or girth
• Increase in leaf area or number of leaves
• Weight of fruits, seeds, or tubers

Development; Development is the progressive qualitative change that occurs in a plant during its life cycle — from seed germination to maturity.

Definition: Development is the sequence of physiological, morphological, and biochemical changes that lead to the formation of specialized structures and functions in plants.

It includes:

• Differentiation – formation of different tissues (xylem, phloem, etc.)
• Morphogenesis – development of shape and form (leaf, flower, fruit)
• Maturation – attainment of reproductive capability

Key Features:

• It is qualitative (not directly measurable).
• It represents functional and structural changes.
• It involves both growth and differentiation.

Difference Between Growth and Development

• Phases of Growth in Crops

Plant growth follows a sigmoid (S-shaped) curve, consisting of four main phases:

1. Lag Phase: Initial slow growth after germination. Cells are small, dividing slowly. Energy used for establishing roots and shoots.
2. Log or Exponential Phase: Rapid growth due to active cell division and enlargement. Maximum increase in dry matter accumulation. Crop shows vigorous vegetative growth.
3. Stationary Phase: Growth rate slows down. Energy and nutrients are redirected toward reproductive organs (flowers and fruits).
4. Senescence Phase: Aging begins; physiological activities decline. Chlorophyll degradation, nutrient remobilization, and tissue death occur.

Measurement of Growth

Plant growth is measured using various indices and parameters.

🔹 Stages of Crop Growth and Development

1. Germination Stage: Activation of enzymes and respiration. Emergence of radicle (root) and plumule (shoot).
2. Seedling Stage: Root system develops, leaves expand. Photosynthetic machinery established.
3. Vegetative Stage: Maximum cell division and elongation. Increase in leaf area, root volume, and plant height.
4. Reproductive Stage: Transition from vegetative to reproductive phase. Flowering, pollination, and fertilization occur.
5. Maturity Stage: Grains or fruits reach physiological maturity. Dry matter accumulation completes.
6. Senescence: Aging of tissues and organs. Decrease in photosynthesis and nutrient uptake.

Factors Affecting Growth and Development

• Plant growth and development are controlled by both internal and external factors.

1. Internal Factors; These include genetic and physiological factors within the plant.

(a) Genetic Makeup: Each species has its own genetic potential for height, yield, and growth duration. E.g., dwarf vs tall wheat varieties; early vs late-maturing rice varieties.

(b) Plant Hormones (Growth Regulators):

(c) Nutrient Availability Within Plant: Adequate supply of macro and micronutrients supports enzyme activity and chlorophyll formation.

• • N → leaf growth
  • P → root and seed development
  • K → disease resistance and water regulation

(d) Source–Sink Relationship:

• Source: Photosynthesizing organs (leaves)
• Sink: Storage or growing organs (grains, roots, tubers)
• Efficient translocation of assimilates determines yield.

2. External (Environmental) Factors

(a) Light:

• Source of energy for photosynthesis.
• Quality (wavelength), intensity, and duration (photoperiod) affect growth.
  • Long-day plants (wheat, barley) flower under >12 hours light.
  • Short-day plants (rice, maize) flower under <12 hours light.

(b) Temperature:

• Affects enzymatic activity, germination, and flowering.
  • Wheat: optimum 20–25°C
  • Rice: optimum 25–30°C
  • High temperature → sterility; Low temperature → dormancy.
• (c) Water: Essential for cell expansion, turgidity, and nutrient transport. Water deficit → reduced leaf area and photosynthesis. Waterlogging → reduced oxygen supply and root growth.
• (d) Air: CO₂ and O₂ play vital roles in photosynthesis and respiration. CO₂ enrichment (700–800 ppm) enhances yield of C₃ crops like wheat and rice.
• (e) Soil: Texture, structure, and fertility affect root penetration and nutrient availability. pH determines nutrient solubility (optimum 6.5–7.5 for most crops).
• (f) Nutrients: Macronutrients (N, P, K, Ca, Mg, S) and Micronutrients (Zn, Fe, Cu, Mn, B, Mo) are essential for metabolic functions.
• (g) Biotic Factors: Pests, diseases, and weeds interfere with nutrient and water uptake. Rhizosphere microorganisms can also influence growth positively (PGPR, Rhizobium).

3. Agronomic and Management Factors

Environmental Adaptation and Growth

Crops exhibit specific growth responses to climatic zones:

• Tropical crops: (e.g., rice, maize, sugarcane) grow best at 25–35°C.
• Temperate crops: (e.g., wheat, barley, oats) prefer 15–25°C.
• Photoperiod sensitivity: Some crops need critical day length for flowering — important for variety selection in different regions.

 Growth Curves and Analysis

The sigmoid (S-shaped) growth curve represents cumulative growth over time:

1. Lag phase – establishment
2. Log phase – rapid increase
3. Stationary phase – leveling off
4. Senescence phase – decline

This helps in understanding growth rates, crop duration, and harvest timing for maximum yield.

Physiological Maturity vs Harvest Maturity

Importance of Understanding Growth and Development

1. Helps in selecting suitable sowing dates and crop varieties for specific climates.
2. Enables better nutrient and irrigation management.
3. Assists in growth regulator application for desired plant behavior.
4. Helps in identifying critical growth stages (like flowering, grain filling) for input use.
5. Supports crop modeling and yield forecasting.

Summary Table of Factors Influencing Growth and Development