The growth and development of plants are governed by their genetic potential as well as interactions with environmental conditions. These factors influence internal physiological processes, which in turn determine yield and productivity. Crop physiology, a branch of plant science, focuses on understanding these internal processes and their practical application in agriculture and horticulture. It covers key functions such as photosynthesis, respiration, transpiration, translocation, nutrient absorption, hormonal regulation, and other mechanisms that directly affect crop yield.
Crop and Crop Physiology
- Crop: A crop refers to a group of plants cultivated together in a particular region for a defined purpose.
- Crop Physiology: Crop physiology studies how various physiological processes integrate at the whole-plant and community level to influence growth, development, and yield. It emphasizes the application of physiological knowledge for efficient crop management.
Historical Development of Crop Physiology
- 1771 – Joseph Priestley: Demonstrated that plants restore oxygen to the atmosphere.
- 1779 – Jan Ingenhousz: Established the role of light in photosynthesis.
- 1804 – De Saussure: Showed that plants absorb minerals and nitrates from soil.
- 1837 – Boussingault: Proved nitrogen uptake by plants from both soil and air.
- 1865 – Julius Sachs: Published Experimentelle Pflanzenphysiologie, establishing plant physiology as a discipline.
- 1915 – W.L. Balls: Initiated crop physiology research on cotton yield; introduced the term "crop physiology".
- 1924 (England): Growth and yield analysis methods developed by Blackman, Gregory, and Briggs.
- 1947 – D.J. Watson: Introduced the concept of Leaf Area Index (LAI).
- 1950s: Infra-Red Gas Analysis (IRGA) developed for estimating photosynthesis and respiration.
- 1963 – Hesketh and Moss: Reported higher photosynthetic rates in maize, sugarcane, and tropical grasses, leading to discovery of C4 and CAM pathways.
Later research emphasized translocation, assimilate partitioning, flowering physiology, stress responses, and the role of growth regulators in productivity improvement.
Significance of Crop Physiology in Agriculture and Horticulture
Crop physiology provides scientific insights into plant functions and helps in formulating improved crop and orchard management practices. Its importance can be understood under the following aspects:
Seed germination and seedling establishment depend on both internal and external factors. Dormancy restricts immediate use of freshly harvested seeds. Treatments such as GA₃ or HNO₃ in paddy seeds are used to break dormancy.
High yield requires greater dry matter production per unit area, which depends on Leaf Area Index (LAI) and Net Assimilation Rate (NAR). Example: Pruning in mango improves canopy structure for better photosynthesis. Yield depends on assimilate partitioning among organs; e.g., excessive vegetative growth in groundnut reduces pod production.
About half of commercial herbicides act by blocking photosynthetic electron transport (e.g., Paraquat, Diuron), stopping CO₂ fixation and killing weeds by starvation.
Plants need 16 essential nutrients for healthy growth. Nutrient physiology helps identify deficiencies and toxicities. Example: Zinc deficiency causes Khaira disease in rice, controlled by zinc sulfate application.
Plant response to day length led to the development of photo-insensitive varieties. Semi-dwarf rice varieties revolutionized Indian agriculture, enabling rice-wheat rotation and expansion into non-traditional areas like Punjab.
Hormones regulate growth, flowering, and fruiting. Example: Indole Butyric Acid (IBA 250 ppm) promotes rooting in stem cuttings for better establishment.
In rainfed agriculture, drought resistance is critical. Traits such as root depth, leaf xeromorphic characters, and high Water Use Efficiency (WUE) are vital. Passioura’s model explains grain yield as:
Grain Yield = T × TE × HI
- T = Total transpiration
- TE = Transpiration efficiency (WUE)
- HI = Harvest index (economic fraction of dry matter)
Moisture and temperature are key factors influencing storage and shelf life. Modified Atmospheric Storage prolongs fruit and vegetable life. Kinetin application in cut flowers delays senescence by reducing ethylene activity.
Crop physiology provides the scientific foundation for understanding plant metabolism, growth, and development. By linking physiological processes with practical applications, it enables crop improvement, stress tolerance, higher productivity, and better post-harvest management in agriculture and horticulture.
