What is allelopathy? Discuss its role in major cropping systems of irrigated agriculture.
Approach · directive: “what / discuss”
What it asks · Define allelopathy and explain its positive and negative effects on crops in irrigated cropping systems such as rice-wheat and sugarcane-based systems.
The question has 2 parts — answer each
- What is allelopathy: define it
- Discuss its role, beneficial and harmful, in major cropping systems of irrigated agriculture
Open with · Allelopathy is the effect, harmful or beneficial, of one plant on another through chemicals it releases into the environment.
Cover
- Meaning: plants release allelochemicals through roots, leaves, residues or leachates; the term was coined by Hans Molisch in 1937; it includes effects on microbes and soil processes.
- Weed suppression: residues and mulches of crops such as sorghum, sunflower and rye, and allelopathic rice and wheat varieties, can reduce weed growth and herbicide use.
- Crop rotation and sequence: the effect of one crop's residue on the next explains why some rotations do well and others give lower yields.
- Negative effects: weeds such as Parthenium and Cyperus release chemicals that reduce crop germination and growth, and tree species in agroforestry may harm associated crops.
- Autotoxicity: repeated planting of the same crop, for example sugarcane ratoons or continuous paddy, can build up self-inhibiting chemicals and cause yield decline.
- Residue management: burning wastes both nutrients and beneficial chemicals; incorporating or mulching straw gives control over weeds while managing possible inhibitory effects.
- Way forward: breed allelopathic cultivars, choose rotations and intercrops carefully, use natural products as bio-herbicides and check harmful effects before promoting them.
Close with · Used wisely, allelopathy can cut chemical use and support sustainable irrigated farming, but its harmful effects must be managed through rotation and residue handling.
Question: UPSC's CS (Main) 2016, GS Paper III — paper ↗. Approach: Minimalist IAS, checked 30 Sept 2026 (how we verify) — UPSC publishes no model answers. ·
Model answer · 240 words (UPSC limit 200) · Minimalist IAS
Allelopathy is the effect, harmful or beneficial, that one plant has on another through chemicals it releases into the environment. The term was coined by Hans Molisch in 1937.
What it involves
- Allelochemicals leave plants through root exudates, leaf leachates, volatiles and decaying residues; they affect germination, growth, soil microbes and nutrient cycling.
Beneficial role in irrigated systems
- Weed suppression: residues and mulches of sorghum, sunflower and rye, and allelopathic rice and wheat varieties, reduce weed growth and herbicide use in rice-wheat and other intensive systems.
- Rotation and intercropping: chemicals left by one crop shape the next, so a well-chosen sequence improves yields and pest control, and allelopathic cover crops keep weeds down in sugarcane-based systems.
- Bio-herbicides: natural allelochemicals can replace part of the synthetic herbicides on which irrigated farming depends.
Harmful role
- Weeds such as Parthenium and Cyperus release chemicals that reduce crop germination and vigour, and agroforestry trees can suppress crops planted beneath them.
- Autotoxicity: continuous paddy and repeated sugarcane ratoons build up self-inhibiting compounds and cause yield decline.
- Residues: incorporating fresh straw of some crops before it decomposes inhibits the following crop, so the timing of residue management matters.
Way forward
- Breed allelopathic cultivars, plan rotations and intercrops, manage residues by mulching or timed incorporation rather than burning, and test effects before promotion.
Used with care, allelopathy can cut chemical use and support sustainable irrigated farming; its harmful side must be managed through rotation and residue handling.
Written by Minimalist IAS from facts checked at source (how we verify) — a little fuller than exam length, so every part of the question is covered; in the hall, keep the structure and trim the detail. UPSC publishes no model answers: compare your structure and coverage with this, then write your own.