This is a classic 'Identify the Legume' test disguised as a science question. Standard texts (NCERT Geography, Shankar Environment) explicitly list Alfalfa, Clover, and Chickpea as nitrogen fixers. The strategy is binary: Is it a legume (pulse/fodder)? Yes = Fixer. Is it a leafy vegetable (Spinach/Amaranth)? No = Consumer.
How this question is built
This question can be broken into the following sub-statements.
Tap a statement sentence to jump into its detailed analysis.
Statement 1
Is alfalfa (Medicago sativa) a nitrogen-fixing plant?
Origin: Direct from books
Fairness: Straightforward
Book-answerable
From standard books
Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > The Nitrogen Cycle > p. 20
Presence: 5/5
“Te nitrogen cycle involves the major constituent of the atmosphere, (78.084 per cent of each breath we take). Nitrogen is also an important element in the formation of organic molecules, especially proteins, and therefore is essential to living processes. A simplifed view of the nitrogen cycle is portrayed in Fig. 1.9. Te vast atmospheric reservoir is however inaccessible directly to most organisms. Te key link to life is provided by nitrogen-fxing bacteria, which live principally in the soil and are associated with the roots of certain plants. For example, the legumes such as alfalfa, beans, clover, pulses, peas, soybeans, green-manuring crops and peanuts.”
Why this source?
- Explicitly lists alfalfa among legumes associated with nitrogen-fixing bacteria.
- Connects legumes (including alfalfa) to root-associated nitrogen fixation used in agriculture.
FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Biological Activity > p. 45
Presence: 4/5
“Further, bacteria and other soil organisms take gaseous nitrogen from the air and convert it into a chemical form that can be used by plants. This process is known as nitrogen fixation. Rhizobium, a type of bacteria, lives in the root nodules of leguminous plants and fixes nitrogen beneficial to the host plant. The influence of large animals like ants, termites, earthworms, rodents etc., is mechanical, but, it is nevertheless important in soil formation as they rework the soil up and down. In case of earthworms, as they feed on soil, the texture and chemistry of the soil that comes out of their body changes.”
Why this source?
- Defines nitrogen fixation by Rhizobium in root nodules of leguminous plants.
- Shows the mechanism by which leguminous hosts obtain fixed nitrogen from bacteria.
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > s r n r u l z N ,- / & f . -. : : u ' , \ S ACADEMY * d 6 # . , r '' t u f Y l ' ' J * w { d ) / u Y . / > p. 20
Presence: 4/5
“& srnrul<zrR ". N ,- / & f. -.:.:u' ,\SACADEMY *d6#.,r'' tufYl' 'J *w{d )/ uY./ include free living nitrifying bacteria (e.g. aerobic Azotobacter and anaerobic Clostridium) and symbiotic nitrifying bacteria living in association with leguminous plants and symbiotic bacteria living in non-leguminous root-nodule plants (e.g., Rhizobium) as well as blue-green algae (e.g., Anabaena, Spirulina). Ammonium ions can be directly taken up as a source of nitrogen by some plants, or are oxidized to nitrites or nitrates by two groups of specialized bacteria: Nitrosomonas bacteria promote transformation of ammonia into nitrite. Nitrite is then further transformed into nitrate by the bacteria Nitrobacter.”
Why this source?
- Describes symbiotic nitrogen-fixing bacteria living in association with leguminous plants.
- Names groups of free-living and symbiotic nitrogen fixers relevant to legumes.
Statement 2
Is amaranth (Amaranthus spp.) a nitrogen-fixing plant?
Origin: Weak / unclear
Fairness: Borderline / guessy
Indirect textbook clues
FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Biological Activity > p. 45
Strength: 5/5
“Further, bacteria and other soil organisms take gaseous nitrogen from the air and convert it into a chemical form that can be used by plants. This process is known as nitrogen fixation. Rhizobium, a type of bacteria, lives in the root nodules of leguminous plants and fixes nitrogen beneficial to the host plant. The influence of large animals like ants, termites, earthworms, rodents etc., is mechanical, but, it is nevertheless important in soil formation as they rework the soil up and down. In case of earthworms, as they feed on soil, the texture and chemistry of the soil that comes out of their body changes.”
Why relevant
Defines nitrogen fixation and states Rhizobium fixes N in root nodules of leguminous plants — establishing a common mechanism tied to legumes.
How to extend
A student can check whether Amaranthus is a legume or forms root nodules (presence would support possible symbiotic fixation).
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > c) The Nitrogen Cycle > p. 19
Strength: 4/5
“(c) The Nitrogen Cycle 0000 00 Nitrogen is an essential constituent of protein and is a basic building block of all living tissue. It constitutes nearly 16% by weight of all the proteins. There is an inexhaustible supply of nitrogen in the atmosphere but the elemental form cannot be used directly by most of the living organisms. Nitrogen needs to be 'fixed', that is, converted to ammonia, nitrites or nitrates, before it can be taken up by plants. Nitrogen fixation on Earth is accomplished in three different ways: • (i) By microorganisms (bacteria and blue-green algae) • (ii) By man using industrial processes (fertilizer factories) and • (iii) To a limited extent by atmospheric phenomenon such as thunder and lighting Certain microorganisms are capable of fixing atmospheric nitrogen into ammonium ions.”
Why relevant
Explains that most plants cannot use atmospheric N directly and lists microorganisms (bacteria, blue‑green algae) as the primary biological fixers.
How to extend
One can investigate whether Amaranthus hosts nitrogen‑fixing bacteria (e.g., nodulating bacteria or cyanobacteria) or relies solely on soil N.
Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > The Nitrogen Cycle > p. 20
Strength: 4/5
“Bacteria colonies reside in nodules on the legume-roots and chemically combine the nitrogen from the air in the form of nitrates (NO3) and ammonia (NH3). Plants use these chemically bound organic matter. Anyone or anything feeding on the plants thus”
Why relevant
Notes bacteria in nodules on legume roots chemically combine atmospheric N into forms plants use — reinforces nodulation as a diagnostic feature.
How to extend
Check root morphology of Amaranthus for nodules or test roots for bacterial symbionts to infer possible fixation.
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > s r n r u l z N ,- / & f . -. : : u ' , \ S ACADEMY * d 6 # . , r '' t u f Y l ' ' J * w { d ) / u Y . / > p. 20
Strength: 4/5
“& srnrul<zrR ". N ,- / & f. -.:.:u' ,\SACADEMY *d6#.,r'' tufYl' 'J *w{d )/ uY./ include free living nitrifying bacteria (e.g. aerobic Azotobacter and anaerobic Clostridium) and symbiotic nitrifying bacteria living in association with leguminous plants and symbiotic bacteria living in non-leguminous root-nodule plants (e.g., Rhizobium) as well as blue-green algae (e.g., Anabaena, Spirulina). Ammonium ions can be directly taken up as a source of nitrogen by some plants, or are oxidized to nitrites or nitrates by two groups of specialized bacteria: Nitrosomonas bacteria promote transformation of ammonia into nitrite. Nitrite is then further transformed into nitrate by the bacteria Nitrobacter.”
Why relevant
Lists free‑living nitrogen fixers (e.g., Azotobacter, Clostridium) and symbiotic bacteria in both leguminous and some non‑leguminous root‑nodule plants and cyanobacteria — indicating multiple possible modes of fixation.
How to extend
A student could determine if Amaranthus associates with free‑living fixers (rhizosphere) or has non‑legume nodulation by checking species‑level literature or root microbiome studies.
Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 9: Agriculture > 11. Less Area under Leguminous and Fodder Crops > p. 9
Strength: 4/5
“The nitrogen fixing crops like pulses are getting less area under their cultivation. Consequently, the natural fertility of the soil is depleting and”
Why relevant
Points out 'nitrogen fixing crops like pulses' are legumes and their decline affects soil fertility — implies that crop taxonomy (legume vs non‑legume) matters for N fixation.
How to extend
Use basic botanical classification to see that Amaranthus belongs to Amaranthaceae (not legumes), which would make classical Rhizobium nodulation unlikely.
Statement 3
Is chickpea (Cicer arietinum) a nitrogen-fixing plant?
Origin: Direct from books
Fairness: Straightforward
Book-answerable
From standard books
NCERT. (2022). Contemporary India II: Textbook in Geography for Class X (Revised ed.). NCERT. > Chapter 4: The Age of Industrialisation > Major Crops > p. 85
Presence: 5/5
“Pulses: India is the largest producer as well as the consumer of pulses in the world. These are the major source of protein in a vegetarian diet. Major pulses that are grown in India are tur (arhar), urad, moong, masur, peas and gram. Can you distinguish which of these pulses are grown in the kharif season and which are grown in the rabi season? Pulses need less moisture and survive even in dry conditions. Being leguminous crops, all these crops except arhar help in restoring soil fertility by fixing nitrogen from the air. Therefore, these are mostly grown in rotation with other crops.”
Why this source?
- Lists gram (chickpea) among pulses and labels these as leguminous crops.
- Explicitly asserts that these leguminous crops (except arhar) restore soil fertility by fixing nitrogen from the air.
FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Biological Activity > p. 45
Presence: 5/5
“Further, bacteria and other soil organisms take gaseous nitrogen from the air and convert it into a chemical form that can be used by plants. This process is known as nitrogen fixation. Rhizobium, a type of bacteria, lives in the root nodules of leguminous plants and fixes nitrogen beneficial to the host plant. The influence of large animals like ants, termites, earthworms, rodents etc., is mechanical, but, it is nevertheless important in soil formation as they rework the soil up and down. In case of earthworms, as they feed on soil, the texture and chemistry of the soil that comes out of their body changes.”
Why this source?
- Explains that Rhizobium bacteria live in root nodules of leguminous plants and fix atmospheric nitrogen.
- Provides the biological mechanism by which leguminous plants obtain usable nitrogen.
Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 9: Agriculture > 11. Less Area under Leguminous and Fodder Crops > p. 9
Presence: 4/5
“The nitrogen fixing crops like pulses are getting less area under their cultivation. Consequently, the natural fertility of the soil is depleting and”
Why this source?
- Refers to pulses as nitrogen-fixing crops, linking the crop category to nitrogen fixation.
- Supports the general classification of pulses (which include chickpea) as contributors to soil nitrogen.
Statement 4
Is clover (Trifolium spp.) a nitrogen-fixing plant?
Origin: Direct from books
Fairness: Straightforward
Book-answerable
From standard books
Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > The Nitrogen Cycle > p. 20
Presence: 5/5
“Te nitrogen cycle involves the major constituent of the atmosphere, (78.084 per cent of each breath we take). Nitrogen is also an important element in the formation of organic molecules, especially proteins, and therefore is essential to living processes. A simplifed view of the nitrogen cycle is portrayed in Fig. 1.9. Te vast atmospheric reservoir is however inaccessible directly to most organisms. Te key link to life is provided by nitrogen-fxing bacteria, which live principally in the soil and are associated with the roots of certain plants. For example, the legumes such as alfalfa, beans, clover, pulses, peas, soybeans, green-manuring crops and peanuts.”
Why this source?
- Explicitly lists clover among legumes that are associated with nitrogen-fixing bacteria.
- Identifies legumes (including clover) as key plants in the biological nitrogen cycle.
FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Biological Activity > p. 45
Presence: 5/5
“Further, bacteria and other soil organisms take gaseous nitrogen from the air and convert it into a chemical form that can be used by plants. This process is known as nitrogen fixation. Rhizobium, a type of bacteria, lives in the root nodules of leguminous plants and fixes nitrogen beneficial to the host plant. The influence of large animals like ants, termites, earthworms, rodents etc., is mechanical, but, it is nevertheless important in soil formation as they rework the soil up and down. In case of earthworms, as they feed on soil, the texture and chemistry of the soil that comes out of their body changes.”
Why this source?
- Explains that Rhizobium bacteria live in root nodules of leguminous plants and fix nitrogen for the host.
- Connects the mechanism (root-nodule symbiosis) to leguminous crops, supporting clover's role.
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > s r n r u l z N ,- / & f . -. : : u ' , \ S ACADEMY * d 6 # . , r '' t u f Y l ' ' J * w { d ) / u Y . / > p. 20
Presence: 4/5
“& srnrul<zrR ". N ,- / & f. -.:.:u' ,\SACADEMY *d6#.,r'' tufYl' 'J *w{d )/ uY./ include free living nitrifying bacteria (e.g. aerobic Azotobacter and anaerobic Clostridium) and symbiotic nitrifying bacteria living in association with leguminous plants and symbiotic bacteria living in non-leguminous root-nodule plants (e.g., Rhizobium) as well as blue-green algae (e.g., Anabaena, Spirulina). Ammonium ions can be directly taken up as a source of nitrogen by some plants, or are oxidized to nitrites or nitrates by two groups of specialized bacteria: Nitrosomonas bacteria promote transformation of ammonia into nitrite. Nitrite is then further transformed into nitrate by the bacteria Nitrobacter.”
Why this source?
- Describes symbiotic nitrogen-fixing bacteria associated with leguminous plants and names Rhizobium.
- Reinforces the general pattern of root-nodule symbiosis in legumes, applicable to clover.
Statement 5
Is purslane (Portulaca oleracea), also called kulfa, a nitrogen-fixing plant?
Origin: Weak / unclear
Fairness: Borderline / guessy
Indirect textbook clues
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > c) The Nitrogen Cycle > p. 19
Strength: 5/5
“(c) The Nitrogen Cycle 0000 00 Nitrogen is an essential constituent of protein and is a basic building block of all living tissue. It constitutes nearly 16% by weight of all the proteins. There is an inexhaustible supply of nitrogen in the atmosphere but the elemental form cannot be used directly by most of the living organisms. Nitrogen needs to be 'fixed', that is, converted to ammonia, nitrites or nitrates, before it can be taken up by plants. Nitrogen fixation on Earth is accomplished in three different ways: • (i) By microorganisms (bacteria and blue-green algae) • (ii) By man using industrial processes (fertilizer factories) and • (iii) To a limited extent by atmospheric phenomenon such as thunder and lighting Certain microorganisms are capable of fixing atmospheric nitrogen into ammonium ions.”
Why relevant
Defines nitrogen fixation and lists the main agents: microorganisms (bacteria and blue‑green algae), industrial processes, and lightning.
How to extend
A student could use this to ask whether purslane is associated with known N‑fixing microorganisms or exposed to such agents in its habitat.
FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Biological Activity > p. 45
Strength: 5/5
“Further, bacteria and other soil organisms take gaseous nitrogen from the air and convert it into a chemical form that can be used by plants. This process is known as nitrogen fixation. Rhizobium, a type of bacteria, lives in the root nodules of leguminous plants and fixes nitrogen beneficial to the host plant. The influence of large animals like ants, termites, earthworms, rodents etc., is mechanical, but, it is nevertheless important in soil formation as they rework the soil up and down. In case of earthworms, as they feed on soil, the texture and chemistry of the soil that comes out of their body changes.”
Why relevant
Explains that Rhizobium in root nodules of leguminous plants fixes nitrogen for the host.
How to extend
A student can check whether purslane is a legume or forms root nodules (if not, this reduces the likelihood of Rhizobium symbiosis).
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > s r n r u l z N ,- / & f . -. : : u ' , \ S ACADEMY * d 6 # . , r '' t u f Y l ' ' J * w { d ) / u Y . / > p. 20
Strength: 4/5
“& srnrul<zrR ". N ,- / & f. -.:.:u' ,\SACADEMY *d6#.,r'' tufYl' 'J *w{d )/ uY./ include free living nitrifying bacteria (e.g. aerobic Azotobacter and anaerobic Clostridium) and symbiotic nitrifying bacteria living in association with leguminous plants and symbiotic bacteria living in non-leguminous root-nodule plants (e.g., Rhizobium) as well as blue-green algae (e.g., Anabaena, Spirulina). Ammonium ions can be directly taken up as a source of nitrogen by some plants, or are oxidized to nitrites or nitrates by two groups of specialized bacteria: Nitrosomonas bacteria promote transformation of ammonia into nitrite. Nitrite is then further transformed into nitrate by the bacteria Nitrobacter.”
Why relevant
Mentions both free‑living nitrogen‑fixing bacteria (e.g., Azotobacter, Clostridium) and symbiotic bacteria including those in non‑leguminous root nodules and cyanobacteria (Anabaena).
How to extend
A student could investigate whether purslane hosts non‑legume root‑nodule symbionts or is commonly associated with free‑living N‑fixers in soil.
Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > The Nitrogen Cycle > p. 20
Strength: 4/5
“Bacteria colonies reside in nodules on the legume-roots and chemically combine the nitrogen from the air in the form of nitrates (NO3) and ammonia (NH3). Plants use these chemically bound organic matter. Anyone or anything feeding on the plants thus”
Why relevant
Describes the general mechanism where bacterial colonies in root nodules chemically bind atmospheric nitrogen to forms plants can use.
How to extend
Use this to test for the physical presence of root nodules or bacterial colonization on purslane roots as evidence for symbiotic fixation.
Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 12: Major Crops and Cropping Patterns in India > 13. Complementrary Crops > p. 12
Strength: 2/5
“Crops which are grown to beneft each other in inter-cropping e.g. Jowar (millets) with Lobiya. Jowar (millets) receives nitrogen from Lobiya and Lobiya requires support from Jowar (millets).”
Why relevant
Gives an example of intercropping where a legume supplies nitrogen to a companion crop, illustrating that nitrogen contribution is commonly from leguminous partners.
How to extend
A student could check whether purslane is ever described as a leguminous companion or as benefiting/adding N in crop rotations.
Statement 6
Is spinach (Spinacia oleracea) a nitrogen-fixing plant?
Origin: Weak / unclear
Fairness: Borderline / guessy
Indirect textbook clues
FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Biological Activity > p. 45
Strength: 5/5
“Further, bacteria and other soil organisms take gaseous nitrogen from the air and convert it into a chemical form that can be used by plants. This process is known as nitrogen fixation. Rhizobium, a type of bacteria, lives in the root nodules of leguminous plants and fixes nitrogen beneficial to the host plant. The influence of large animals like ants, termites, earthworms, rodents etc., is mechanical, but, it is nevertheless important in soil formation as they rework the soil up and down. In case of earthworms, as they feed on soil, the texture and chemistry of the soil that comes out of their body changes.”
Why relevant
Defines nitrogen fixation and states that Rhizobium bacteria live in root nodules of leguminous plants to fix nitrogen for the host.
How to extend
A student can check whether spinach is a legume or forms root nodules with Rhizobium — if not, it is unlikely to be a Rhizobium-based nitrogen-fixer.
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > c) The Nitrogen Cycle > p. 19
Strength: 4/5
“(c) The Nitrogen Cycle 0000 00 Nitrogen is an essential constituent of protein and is a basic building block of all living tissue. It constitutes nearly 16% by weight of all the proteins. There is an inexhaustible supply of nitrogen in the atmosphere but the elemental form cannot be used directly by most of the living organisms. Nitrogen needs to be 'fixed', that is, converted to ammonia, nitrites or nitrates, before it can be taken up by plants. Nitrogen fixation on Earth is accomplished in three different ways: • (i) By microorganisms (bacteria and blue-green algae) • (ii) By man using industrial processes (fertilizer factories) and • (iii) To a limited extent by atmospheric phenomenon such as thunder and lighting Certain microorganisms are capable of fixing atmospheric nitrogen into ammonium ions.”
Why relevant
Gives the general rule that nitrogen fixation is carried out by microorganisms (bacteria and blue‑green algae), industrial processes, or lightning, implying plants fix nitrogen only via microbial symbiosis or special associations.
How to extend
A student could ask whether spinach hosts nitrogen‑fixing microorganisms (symbiotic or endophytic) or relies on soil/industrial sources instead.
Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > s r n r u l z N ,- / & f . -. : : u ' , \ S ACADEMY * d 6 # . , r '' t u f Y l ' ' J * w { d ) / u Y . / > p. 20
Strength: 4/5
“& srnrul<zrR ". N ,- / & f. -.:.:u' ,\SACADEMY *d6#.,r'' tufYl' 'J *w{d )/ uY./ include free living nitrifying bacteria (e.g. aerobic Azotobacter and anaerobic Clostridium) and symbiotic nitrifying bacteria living in association with leguminous plants and symbiotic bacteria living in non-leguminous root-nodule plants (e.g., Rhizobium) as well as blue-green algae (e.g., Anabaena, Spirulina). Ammonium ions can be directly taken up as a source of nitrogen by some plants, or are oxidized to nitrites or nitrates by two groups of specialized bacteria: Nitrosomonas bacteria promote transformation of ammonia into nitrite. Nitrite is then further transformed into nitrate by the bacteria Nitrobacter.”
Why relevant
Lists types of nitrogen‑fixing bacteria: free‑living (Azotobacter, Clostridium), symbiotic with legumes, and symbiotic bacteria in non‑legume root nodules, showing multiple biological modes but emphasizing specific associations.
How to extend
A student can investigate whether spinach is known to associate with any of these free‑living or symbiotic nitrogen‑fixers or to develop root nodules.
Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > The Nitrogen Cycle > p. 20
Strength: 4/5
“Bacteria colonies reside in nodules on the legume-roots and chemically combine the nitrogen from the air in the form of nitrates (NO3) and ammonia (NH3). Plants use these chemically bound organic matter. Anyone or anything feeding on the plants thus”
Why relevant
Explains bacteria in nodules on legume roots chemically combine atmospheric nitrogen into forms plants use, reinforcing the pattern that nodulation is a key indicator of plant nitrogen‑fixing partnerships.
How to extend
A student could examine spinach root morphology (presence/absence of nodules) or literature on nodulation to assess whether it participates in this typical pathway.
Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 20: Earths Atmosphere > Life-giving gases > p. 280
Strength: 3/5
“• Plants require carbon dioxide to survive while animals and many other organisms need oxygen for their survival. Nitrogen is fixed by bacteria and lightning to produce ammonia used in the construction of nucleotides and amino acids.”
Why relevant
Notes that nitrogen is fixed by bacteria (and lightning), underscoring that fixation is usually an abiotic or microbial process rather than a direct plant trait.
How to extend
A student might therefore check whether spinach itself biochemically fixes N (unlikely from this rule) or instead depends on microbial/abiotic fixed nitrogen in soil.
Pattern takeaway:
UPSC tests 'Applied Botany' through the lens of Agriculture. They don't ask for the bacterial strain name (Rhizobium vs Azotobacter) as often as they ask for the host plant. The pattern is to mix common kitchen ingredients (Spinach, Chickpea) with fodder crops (Alfalfa, Clover) to test observation skills.
How you should have studied
- [THE VERDICT]: Sitter. Direct hit from NCERT Class X Geography (Ch 4) and Shankar IAS (Ch 2). If you missed this, your basic reading of 'Leguminous Crops' is weak.
- [THE CONCEPTUAL TRIGGER]: Bio-geochemical Cycles (Nitrogen Cycle) and Sustainable Agriculture (Biofertilizers).
- [THE HORIZONTAL EXPANSION]: Memorize the 'Fixer Squad': Legumes (Peas, Beans, Soy, Alfalfa, Clover, Gliricidia), Non-Legumes (Casuarina, Alder), and Aquatic (Azolla-Anabaena). Contrast with 'Nitrogen Hogs' (Spinach, Maize, Cotton).
- [THE STRATEGIC METACOGNITION]: When reading about the Nitrogen Cycle, stop treating 'Legumes' as a generic word. Unpack the category: What are the specific examples mentioned in NCERT? (Gram, Tur, Urad, Moong, Peas). Add fodder crops (Alfalfa, Clover) from Ecology texts.
Concept hooks from this question
👉 Legumes as nitrogen-fixing crops
💡 The insight
Leguminous plants (e.g., alfalfa) are commonly associated with root bacteria that fix atmospheric nitrogen.
High-yield for questions on soil fertility, crop choice and sustainable agriculture. Links agriculture to biogeochemical cycles and cropping systems; useful for MCQs and short-answer questions on crops that improve soil nitrogen.
📚 Reading List :
- Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > The Nitrogen Cycle > p. 20
- FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Biological Activity > p. 45
🔗 Anchor: "Is alfalfa (Medicago sativa) a nitrogen-fixing plant?"
👉 Rhizobium and root-nodule symbiosis
💡 The insight
Rhizobium bacteria form root nodules on legumes and convert atmospheric nitrogen into plant-usable forms.
Essential for explaining mechanisms behind biological nitrogen fixation; connects microbiology with agronomy and environmental science topics. Enables answers on biofertility, crop rotations and soil nutrient management.
📚 Reading List :
- FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Biological Activity > p. 45
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > s r n r u l z N ,- / & f . -. : : u ' , \ S ACADEMY * d 6 # . , r '' t u f Y l ' ' J * w { d ) / u Y . / > p. 20
🔗 Anchor: "Is alfalfa (Medicago sativa) a nitrogen-fixing plant?"
👉 Bio-fertilizers and nitrogen-fixing microorganisms
💡 The insight
Bio-fertilizers contain live nitrogen-fixing microbes used to augment plant-available nitrogen.
Relevant to policy and practice questions on sustainable farming and fertilizer alternatives; links to chapters on agriculture, soil management and eco-friendly inputs, and helps frame solutions-based answers.
📚 Reading List :
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 25: Agriculture > Bio-fertilizers > p. 364
- Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > The Nitrogen Cycle > p. 20
🔗 Anchor: "Is alfalfa (Medicago sativa) a nitrogen-fixing plant?"
👉 Modes of nitrogen fixation
💡 The insight
Nitrogen is fixed into biologically available forms by microorganisms, industrial processes, and atmospheric phenomena.
High-yield concept for questions on nutrient cycles, agriculture and environmental management; helps answer questions on sources of soil nitrogen, fertilizer policy, and ecosystem functioning. Mastering this enables candidates to link biological processes to agricultural inputs and policy debates.
📚 Reading List :
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > c) The Nitrogen Cycle > p. 19
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 25: Agriculture > Bio-fertilizers > p. 364
🔗 Anchor: "Is amaranth (Amaranthus spp.) a nitrogen-fixing plant?"
👉 Symbiotic nitrogen fixation in root nodules
💡 The insight
Rhizobium bacteria form root nodules on legumes and fix nitrogen; symbiotic root-nodule associations can occur in non-leguminous plants as well.
Essential for questions on crop selection, soil fertility restoration, and sustainable farming (e.g., crop rotation with legumes). It connects ecology, agriculture and rural economy topics and helps reason about which crops contribute to soil nitrogen.
📚 Reading List :
- FUNDAMENTALS OF PHYSICAL GEOGRAPHY, Geography Class XI (NCERT 2025 ed.) > Chapter 5: Geomorphic Processes > Biological Activity > p. 45
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 2: Functions of an Ecosystem > s r n r u l z N ,- / & f . -. : : u ' , \ S ACADEMY * d 6 # . , r '' t u f Y l ' ' J * w { d ) / u Y . / > p. 20
🔗 Anchor: "Is amaranth (Amaranthus spp.) a nitrogen-fixing plant?"
👉 Biofertilizers and microbial augmentation of soil nitrogen
💡 The insight
Biofertilizers contain live nitrogen-fixing microorganisms applied to seeds or soil to increase microbial nitrogen-fixation processes.
Directly relevant for policy and practice questions on sustainable agriculture, reducing chemical fertilizer use, and improving soil health. Understanding this concept allows candidates to discuss interventions (biofertilizers) for augmenting soil fertility.
📚 Reading List :
- Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 25: Agriculture > Bio-fertilizers > p. 364
- Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > The Nitrogen Cycle > p. 20
🔗 Anchor: "Is amaranth (Amaranthus spp.) a nitrogen-fixing plant?"
👉 Leguminous pulses fix atmospheric nitrogen
💡 The insight
Pulses such as gram (chickpea) are leguminous and fix atmospheric nitrogen, restoring soil fertility.
High-yield for agriculture and environment questions: explains why pulses are prioritized in crop planning and soil management. Links to topics on sustainable agriculture, food security, and cropping patterns; useful for questions on soil fertility and crop choices.
📚 Reading List :
- NCERT. (2022). Contemporary India II: Textbook in Geography for Class X (Revised ed.). NCERT. > Chapter 4: The Age of Industrialisation > Major Crops > p. 85
- Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 9: Agriculture > 11. Less Area under Leguminous and Fodder Crops > p. 9
🔗 Anchor: "Is chickpea (Cicer arietinum) a nitrogen-fixing plant?"
Frankia & Casuarina. While everyone knows Rhizobium+Legumes, the Frankia bacteria fixes nitrogen in non-leguminous trees like Casuarina and Alnus. This is the next logical 'hard' question.
The 'Leafy Green' Logic. Spinach and Amaranth are grown for their lush green leaves. Biologically, rapid leaf growth requires *consuming* massive amounts of soil nitrogen (nitrates). If they fixed their own, they wouldn't be such heavy feeders. Also, Alfalfa and Clover are famous 'Green Manure' crops—Spinach is never used as green manure.
GS-3 Agriculture & Economy. Nitrogen fixing plants = Reduced Urea Import Bill. Linking natural N-fixation to the government's 'Soil Health Card' and 'Neem Coated Urea' schemes creates a holistic answer for Mains.