Crop Science and Cropping Systems
The science behind crops and cropping systems: C3 and C4 plants, photoperiod, intercropping, rotation, SRI, DSR, conservation agriculture and utera for CGPSC Mains.
Prerequisites
- Cropping Seasons and Farming Systems: kharif, rabi and zaid, cropping intensity and the vocabulary of mixed and relay cropping. This page assumes it and adds the science
- Rice Bowl of India: Cropping Pattern: what Chhattisgarh actually grows, and the practice of utera
- Biology and Health: photosynthesis and plant nutrition at school level
The Hook: Why Does a Farmer in Durg Plough His Growing Paddy?
Travel through the Chhattisgarh plain in late July and you may see a strange sight: a farmer running a plough through a field of young, broadcast paddy. This is biasi (बियासी). It looks destructive, but it thins the crop, buries weeds and loosens the soil. In October, the same farmer may scatter lathyrus (तिवड़ा) seed into the ripening paddy so that a second crop sprouts on the leftover moisture. This is utera (उतेरा).
Both are traditional answers to scientific questions. How do plants use light, water and nitrogen? Which crops help each other and which compete? How can one field give two harvests without irrigation? This page gives the science behind those answers.
Why it matters: Mains GS-II Part 3 (Applied Science) asks why a practice works, not only what it is called. Expect questions such as “explain the scientific basis of crop rotation”, “SRI versus conventional paddy”, or “conservation agriculture as a climate response”. Geography covers where crops grow and economy covers policy. This page covers how crops grow.
How Crops Are Classified
| Basis | Classes | Examples |
|---|---|---|
| Use (agronomic) | Cereals, millets, pulses, oilseeds, fibre, sugar, fodder, plantation, spices | Rice, kodo, gram, mustard, cotton, sugarcane, berseem |
| Botanical family | Poaceae (grasses), Fabaceae (legumes), Brassicaceae, Malvaceae | Rice and maize (Poaceae); gram and soybean (Fabaceae); mustard (Brassicaceae); cotton (Malvaceae) |
| Season | Kharif, rabi, zaid | Paddy (kharif), wheat and gram (rabi), watermelon (zaid) |
| Photoperiod response | Short-day, long-day, day-neutral | Rice, soybean (short-day); wheat, mustard (long-day); many modern hybrids are nearly day-neutral |
| Photosynthetic pathway | C3, C4, CAM | Rice and wheat (C3); maize, sugarcane, sorghum (C4); pineapple (CAM) |
| Life span | Annual, biennial, perennial | Paddy (annual), sugarcane (grown as a multi-year ratoon crop) |
C3, C4 and CAM: the photosynthesis question
| Feature | C3 plants | C4 plants | CAM plants |
|---|---|---|---|
| First stable product of carbon fixation | A 3-carbon compound (3-phosphoglyceric acid) | A 4-carbon compound (oxaloacetate) | 4-carbon acid, formed at night |
| CO₂-fixing enzyme | RuBisCO only | PEP carboxylase first, then RuBisCO in bundle-sheath cells | PEP carboxylase at night, RuBisCO by day |
| Leaf anatomy | No distinct bundle sheath | Kranz anatomy (क्रांज़ शारीरिकी): a ring of bundle-sheath cells | Succulent tissue |
| Photorespiration | High, especially in heat | Very low | Very low |
| Best suited to | Cool, moist conditions | Hot, sunny, dry conditions | Arid conditions |
| Water-use efficiency | Lower | Higher | Highest |
| Crops | Rice, wheat, pulses, oilseeds, cotton | Maize, sugarcane, sorghum, pearl millet, many millets | Pineapple, agave |
Why it matters for agriculture: C4 crops lose less energy to photorespiration, so they make more dry matter per unit of water and sunlight in hot climates. This is one scientific reason why millets (कोदो, कुटकी, रागी) are promoted as climate-resilient crops. It is also why the international C4 Rice Project tries to engineer C4 traits into rice, which is a C3 plant.
Growth stages that decide yield
For cereals such as rice, yield is built in stages, and stress at each stage costs something different:
| Stage (rice) | What happens | Stress at this stage causes |
|---|---|---|
| Seedling and tillering (कल्ले निकलना) | Plant makes side shoots (tillers) | Fewer tillers, hence fewer panicles |
| Panicle initiation to booting | Ear forms inside the stem | Fewer grains per panicle |
| Flowering (anthesis) | Pollination | Spikelet sterility (heat or drought here is the most damaging) |
| Grain filling to maturity | Starch moves into grain | Light, chaffy grains |
This is why irrigation scheduling and nitrogen top-dressing are timed to critical stages, not to the calendar.
Cropping Systems: the Science Behind Them
A cropping pattern is the proportion of area under different crops at a given time. A cropping system is the pattern plus the way it is managed: sequence, combination, inputs and technology. The geography chapter lists the types. Here is why each works.
| System | What it is | Scientific basis |
|---|---|---|
| Monocropping | Same crop on the same land year after year | Simple to manage, but builds up the crop’s own pests and diseases and mines the same nutrients from the same root zone |
| Crop rotation (फसल चक्र) | Different crops in a planned sequence | Breaks pest and disease cycles; deep-rooted crops follow shallow-rooted ones; a legume in the rotation adds nitrogen |
| Intercropping (अंतरवर्ती खेती) | Two or more crops in rows at the same time | Complementarity: different root depths, heights, durations and nutrient needs use resources more fully. Example: arhar + soybean, maize + legume |
| Mixed cropping | Seeds mixed and sown together without rows | Mainly insurance against total crop failure in rainfed areas |
| Relay cropping | Second crop sown into the standing first crop before its harvest | Uses residual soil moisture and saves time. Utera is a Chhattisgarh example |
| Sequential cropping | Two or more crops one after the other in a year | Raises cropping intensity; needs irrigation or a long wet season |
| Ratooning | New crop grown from the stubble of the harvested one | Saves seed and land preparation. Common in sugarcane |
| Agroforestry | Trees with crops or livestock | Trees recycle nutrients from deep layers, reduce erosion, add income and store carbon |
Why legumes fix nitrogen
Legumes such as gram, arhar, soybean and lathyrus host Rhizobium bacteria in root nodules (ग्रंथिकाएँ). The bacteria carry the enzyme nitrogenase, which converts atmospheric nitrogen (N₂) into ammonia that the plant can use. Nitrogenase is damaged by oxygen, so the nodule contains leghaemoglobin, an oxygen-binding pigment that gives active nodules their pink colour. When the crop’s roots and leaves decompose, some of this nitrogen is left for the next crop. This is the scientific core of crop rotation and of the “pulses after paddy” advice. (Biofertilisers are covered in Soil Fertility, Fertilisers and Manures.)
Measuring the gain: Land Equivalent Ratio
The Land Equivalent Ratio (LER) compares an intercrop with sole crops:
$$\text{LER} = \frac{Y_{A,\text{inter}}}{Y_{A,\text{sole}}} + \frac{Y_{B,\text{inter}}}{Y_{B,\text{sole}}}$$where \( Y \) is yield. An LER above 1 means intercropping gives more output from the same land than growing each crop separately. For example, if an intercrop gives 80% of sole maize yield and 50% of sole soybean yield, LER = 0.8 + 0.5 = 1.3: one hectare of intercrop equals 1.3 hectares of sole crops.
Rice Systems: Puddled, SRI and Direct-Seeded
Rice dominates Chhattisgarh, and Mains questions on water, methane and labour all meet in the paddy field.
| Method | How it works | Strengths | Weaknesses |
|---|---|---|---|
| Puddled transplanted rice (रोपा) | Field flooded and churned (puddled); nursery seedlings transplanted | Puddling cuts water seepage and suppresses weeds | Very water- and labour-intensive; standing water produces methane |
| Broadcast rice with biasi (बोता + बियासी) | Seed broadcast on dry or moist soil; once the field has standing rainwater, roughly 30–40 days after sowing, the young crop is cross-ploughed | Low cost; biasi buries weeds, thins the crop and loosens soil | Uneven stand; lower yield than well-managed transplanting |
| System of Rice Intensification (SRI) | Young seedlings (8–12 days), single seedlings at wide spacing, alternate wetting and drying, mechanical weeding, organic matter | Less seed and water; strong roots and tillering | Needs skilled labour and good water control |
| Direct-Seeded Rice (DSR) | Seed sown directly by seed drill, no nursery or puddling | Saves labour and water; earlier harvest; lower methane | Heavy weed pressure; needs herbicides and precise levelling |
| Alternate Wetting and Drying (AWD) | Field allowed to dry until water drops a few centimetres below the soil surface, then re-flooded | Saves irrigation water; cuts methane | Needs assured irrigation to re-flood on time |
Methane link: In flooded paddy soil, oxygen runs out and methanogenic archaea decompose organic matter into methane (CH₄), a potent greenhouse gas. Any method that lets the soil breathe (AWD, SRI, DSR) reduces methane. This is why rice is central to agricultural climate debates. See Climate Change.
Conservation Agriculture and Climate-Smart Systems
Conservation agriculture (संरक्षण कृषि), as defined by the FAO, rests on three principles:
- Minimum soil disturbance: zero or reduced tillage
- Permanent soil cover: crop residues or cover crops on the surface
- Crop diversification: rotations and intercrops
Why it works: Undisturbed soil keeps its structure and organic carbon. Residue cover cuts evaporation and erosion and feeds soil organisms. Diversity breaks pest cycles.
Indian examples:
- Zero-till wheat after rice in the Indo-Gangetic plains, using machines such as the Happy Seeder, which sows wheat through standing rice stubble. It is a scientific alternative to stubble burning.
- Mulching and residue retention in rainfed areas.
- Millets and pulses in place of a second paddy crop where water is short.
- Climate and water: rainfall amount and distribution, irrigation access
- Soil: texture and water-holding capacity (clayey Kanhar soils hold moisture for utera; sandy Bhata soils do not)
- Crop physiology: C3 or C4 pathway, photoperiod response, rooting depth, duration
- Biotic factors: pests, diseases and weeds that build up under monocropping
- Economics and policy: assured procurement of paddy at MSP pulls farmers towards rice monoculture (see MSP and Procurement)
The Chhattisgarh angle
- Paddy monoculture on the plains means high pest build-up, high water demand and fallow land in rabi. Utera and crop diversification towards pulses, oilseeds and millets are the scientific counters.
- Utera works because clayey Kanhar and Dorsa soils keep moisture after the paddy is harvested, and legumes such as lathyrus add nitrogen. Its limit: lathyrus seed contains the neurotoxin ODAP (β-ODAP), which can cause neurolathyrism if eaten as a staple for long periods. Low-toxin varieties have been bred for this reason.
- Indira Gandhi Krishi Vishwavidyalaya (IGKV), Raipur (इंदिरा गांधी कृषि विश्वविद्यालय), the state agricultural university, works on rice-based cropping systems, utera and millets for the three agro-climatic zones. See Agro-Climatic Zones of Chhattisgarh.
Memory Tricks
Don’t Confuse
| This | vs | That |
|---|---|---|
| Intercropping: crops in definite rows, planned | vs | Mixed cropping: seeds mixed, no row pattern, mainly insurance |
| Relay cropping (utera): second crop sown into standing first crop | vs | Sequential cropping: second crop sown after first is harvested |
| Biasi: ploughing a standing young paddy crop (July–August) | vs | Utera: broadcasting a second crop into ripening paddy (October) |
| C4: Kranz anatomy, PEP carboxylase, low photorespiration | vs | CAM: stomata open at night, for arid succulents |
| Short-day plant (rice): flowers when nights lengthen | vs | Long-day plant (wheat): flowers when days lengthen |
| Cropping pattern: share of area under crops | vs | Cropping system: pattern plus sequence and management |
Common Mistakes
- “Rice is a C4 plant.” False. Rice is C3. Maize, sugarcane and sorghum are C4.
- “Legumes fix nitrogen themselves.” Imprecise. Rhizobium bacteria in the root nodules fix it, using the enzyme nitrogenase. The plant supplies sugar and leghaemoglobin.
- “SRI needs more water.” False. SRI uses less water because the field is not kept continuously flooded.
- “DSR has no drawbacks.” False. Its main problem is weeds, because there is no standing water to suppress them.
- “Conservation agriculture means organic farming.” False. It is about tillage, cover and rotation. A conservation-agriculture field may still use chemical fertilisers and herbicides.
Practice
All questions below are original practice questions written in CGPSC style. They are not previous-year questions.
Level 1: Foundation
- The leaf anatomy with a ring of bundle-sheath cells, typical of C4 plants, is called ______ anatomy.
- The enzyme that fixes atmospheric nitrogen in legume root nodules is ______.
- The Chhattisgarh practice of ploughing a standing young paddy crop is called ______.
Answers
- Kranz anatomy.
- Nitrogenase.
- Biasi (बियासी).
Level 2: Prelims-style MCQs
Q1. Consider the following statements about C4 plants:
- They fix carbon dioxide first into a four-carbon compound.
- They show higher photorespiration than C3 plants in hot conditions.
- Maize and sugarcane are C4 plants.
Which of the statements given above is/are correct?
- (a) 1 only
- (b) 1 and 3 only
- (c) 2 and 3 only
- (d) 1, 2 and 3
Answer and explanation
Q2. Match List I (Practice) with List II (Description):
| List I | List II |
|---|---|
| A. Utera | 1. Sowing seed directly by drill without a nursery or puddling |
| B. SRI | 2. Broadcasting a second crop into ripening paddy |
| C. DSR | 3. Single young seedlings, wide spacing, intermittent irrigation |
| D. Ratooning | 4. Raising a crop from the stubble of a harvested crop |
- (a) A-2, B-3, C-1, D-4
- (b) A-3, B-2, C-1, D-4
- (c) A-2, B-1, C-3, D-4
- (d) A-4, B-3, C-1, D-2
Answer and explanation
Q3. Which of the following is not one of the three principles of conservation agriculture as defined by the FAO?
- (a) Minimum soil disturbance
- (b) Permanent organic soil cover
- (c) Crop diversification
- (d) Exclusive use of organic fertilisers
Answer and explanation
Q4. An intercrop of maize and soybean gives 90% of the sole maize yield and 40% of the sole soybean yield. What is its Land Equivalent Ratio, and what does it indicate?
- (a) 0.65; intercropping is less efficient
- (b) 1.30; intercropping is more efficient
- (c) 1.30; intercropping is less efficient
- (d) 0.50; the two crops compete strongly
Answer and explanation
Q5. Methane emission from rice fields falls under alternate wetting and drying mainly because:
- (a) Drying kills the rice roots that produce methane
- (b) Aerobic periods suppress methanogenic archaea in the soil
- (c) Less fertiliser is used
- (d) The crop is harvested earlier
Answer and explanation
Level 3: Mains Answer Writing
Q1. (60 words) Explain the scientific basis of crop rotation with legumes.
Model answer outline
- Legumes host Rhizobium in root nodules; nitrogenase fixes atmospheric N₂ into ammonia, protected by leghaemoglobin.
- Residues leave nitrogen for the next crop, cutting urea need.
- Rotation also breaks pest and disease cycles and alternates rooting depth.
- Example: gram or lathyrus after paddy in Chhattisgarh, often sown as utera.
Q2. (150–200 words) “Paddy monoculture is agronomically and environmentally unsustainable.” Examine the scientific alternatives available to a rice-dominated state such as Chhattisgarh.
Model answer outline
- Intro: Chhattisgarh’s plains are dominated by kharif paddy, with much land fallow in rabi; one crop, one season, heavy water use.
- Problems (science): pest and disease build-up (stem borer, gall midge, brown planthopper); nutrient mining of the same root zone; methane from flooded fields; groundwater stress where rabi paddy spreads.
- Alternatives:
- Crop rotation and utera with legumes (lathyrus, gram, lentil), using residual moisture of clayey Kanhar–Dorsa soils and adding nitrogen.
- SRI and AWD: less seed and water, lower methane.
- DSR with integrated weed management to save labour and water.
- Crop diversification to millets (C4, drought-tolerant), pulses and oilseeds on upland Bhata and Matasi soils.
- Conservation agriculture: minimum tillage, residue cover.
- Constraints: MSP and procurement bias towards paddy, stray cattle damaging rabi crops, market gaps for pulses and millets.
- Conclusion: Science offers the tools; a shift in incentives and extension (IGKV, KVKs) must follow.
Quick Revision Table
| Fact | Detail |
|---|---|
| C3 crops | Rice, wheat, pulses; RuBisCO only; high photorespiration in heat |
| C4 crops | Maize, sugarcane, sorghum, millets; Kranz anatomy; PEP carboxylase |
| CAM | Pineapple; stomata open at night |
| Short-day crops | Rice, soybean |
| Nitrogen fixation | Rhizobium, nitrogenase, leghaemoglobin (pink nodules) |
| LER > 1 | Intercropping more land-efficient than sole cropping |
| SRI | Madagascar, 1980s, Henri de Laulanié; young single seedlings, wide spacing, AWD |
| DSR | No nursery, no puddling; weeds are the main problem |
| Paddy methane | Methanogenic archaea in anaerobic soil |
| Conservation agriculture | Minimum tillage + soil cover + diversification (FAO) |
| Biasi | Cross-ploughing standing broadcast paddy (Chhattisgarh) |
| Utera | Relay sowing of lathyrus, linseed, gram into ripening paddy |
| Lathyrus toxin | β-ODAP, causes neurolathyrism |
Key Takeaways
- Crop physiology (C3/C4, photoperiod, critical growth stages) explains where and when crops do best.
- Every cropping system has a scientific logic: complementarity in intercropping, nitrogen and pest-cycle breaks in rotation, residual moisture in relay cropping.
- Flooded rice is a methane source. SRI, AWD and DSR cut water use and emissions, each with trade-offs.
- Conservation agriculture means minimum tillage, soil cover and diversification, not “organic”.
- Chhattisgarh’s own practices, biasi and utera, are science-backed answers to rainfed conditions.
What’s Next
- Seed Technology and Crop Improvement: how better varieties, hybrids and GM or genome-edited crops are made
- Soil Fertility, Fertilisers and Manures: feeding the crop
- Green Revolution: how high-yielding varieties changed Indian cropping
- Agriculture and Irrigation in Chhattisgarh: the state’s crops, zones and schemes