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.
It asks 2 things — answer each
- What is allelopathy: define it
- Discuss its role, beneficial and harmful, in major cropping systems of irrigated agriculture
Open with · Allelopathy, from the Greek allelo and pathy, is the harmful or beneficial effect of one plant on another through released chemicals; the term was first used in 1937 by Hans Molisch.
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 · Managed knowingly, allelopathy becomes a free input for sustainable intensification: fewer herbicides, less straw burning and steadier yields in irrigated belts.
Add value (verified)
- University of Florida IFAS Extension: the term allelopathy (Greek allelo and pathy, 'mutual harm') was first used in 1937 by Austrian scientist Hans Molisch. ↗“The term allelopathy is from the Greek-derived compounds allelo and pathy (meaning “mutual harm” or “suffering”) and was first used in 1937 by Austrian scientist Hans Molisch”
- IFAS: allelochemicals identified in weed suppression include benzoxanoids in rye and diterpenoid momilactones in rice. ↗“Studies have eluci- dated specific allelochemicals involved in weed suppression, including benzoxanoids in rye; diterpenoid momilactones in rice”
- IFAS: a genetic basis of allelopathy is demonstrated in winter wheat and rice, with cultivars of increased allelopathic potential known in both. ↗“Genetic basis of allelopathy has now been demonstrated in winter wheat and rice. Specific cultivars with increased allelopathic potential are known in both these crops”
- IFAS: an extract of brassica, sorghum and sunflower applied to rain-fed wheat reduced weed pressure. ↗“an extract of brassica (Brassica napus), sorghum, and sunflower was used on rain-fed wheat to successfully reduce weed pressure”
- IFAS: Leucaena species reduce the yield of wheat but increase the yield of rice. ↗“Leucaena species have also been shown to reduce the yield of wheat but increase the yield of rice”
Question: UPSC's CS (Main) 2016, GS Paper III — paper ↗. Approach: Minimalist IAS, checked 3 Oct 2026 (how we verify) — UPSC publishes no model answers. ·
Model answer· 287words · Minimalist IAS
Allelopathy, from the Greek allelo and pathy ('mutual harm'), is the effect, harmful or beneficial, of one plant on another through chemicals it releases. The term was first used in 1937 by the Austrian scientist Hans Molisch (University of Florida IFAS Extension). In irrigated rice-wheat and sugarcane systems these allelochemicals shape weeds, rotations and yields.
What allelopathy involves
- Release routes: root exudates, leaf leachates, volatiles and decaying residues.
- Targets: germination, seedling growth, soil microbes and nutrient cycling.
Beneficial role in irrigated cropping systems
- Weed suppression: momilactones in rice and benzoxazinoids in rye suppress weeds; allelopathic cultivars with a proven genetic basis exist in rice and winter wheat.
- Residues and extracts: sorghum, sunflower and brassica extracts reduced weed pressure in rain-fed wheat (IFAS); crop residues and mulches cut herbicide use.
- Rotation design: the residue of one crop shapes the next, so a well-chosen sequence raises yields and lowers pest and weed load.
- Bio-herbicides: natural allelochemicals offer leads for new, less persistent herbicides.
Harmful role
- Weed allelopathy: Parthenium and Cyperus release chemicals that reduce crop germination and vigour.
- Agroforestry: Leucaena reduces wheat yield though it raises rice yield (IFAS), so tree-crop pairing matters.
- Autotoxicity: continuous paddy and repeated sugarcane ratoons build self-inhibiting compounds and yield decline.
- Residue timing: fresh straw incorporated before it decomposes inhibits the following crop.
| Effect | Example | Management |
|---|---|---|
| Weed control | rice momilactones | allelopathic cultivars |
| Crop injury | Leucaena on wheat | choose intercrops |
| Autotoxicity | sugarcane ratoon | rotate, manage residue |
Way forward
- Use it knowingly: breed allelopathic cultivars, plan rotations and intercrops, mulch or time residue incorporation instead of burning, and test effects before promotion.
Managed with this knowledge, allelopathy becomes a free input for sustainable intensification: fewer herbicides, less straw burning and steadier yields in India's irrigated belts.
Prepared by Minimalist IAS to the answer standard of Shivam Singh (mentor, 7 years) · facts checked against official sources (how we verify) · updated 3 Oct 2026. UPSC publishes no model answers: compare your structure and coverage with this, then write your own.
