Which one of the following plants is used for green manuring in India ?

1. Soil Fertility and Nutrient Management in India (basic)

To understand sustainable farming, we must start with the foundation of all agriculture: Soil Fertility. Think of soil not just as dirt, but as a living biological factory. Soil fertility is the inherent capacity of the soil to supply essential nutrients to plants in adequate amounts and proper balance. In the Indian context, managing this fertility is a delicate balancing act between chemical inputs and organic replenishment.

Plants primarily require three macro-nutrients: Nitrogen (N) for leaf growth, Phosphorus (P) for root and flower development, and Potassium (K) for overall plant health. While the ideal N:P:K ratio for Indian soils is generally considered to be 4:2:1, the actual usage often skews heavily toward Nitrogen due to the high consumption of Urea. In India, the government regulates the price of Urea, while other major fertilizers like Diammonium Phosphate (DAP) and Muriate of Potash (MoP) operate under a Nutrient Based Subsidy (NBS) regime, where the subsidy is fixed based on the nutrient content Indian Economy, Vivek Singh, Subsidies, p.287.

Sustainable management, however, moves beyond just bags of chemicals. Green Manuring is a cornerstone of this approach. It involves growing specific crops—largely legumes—and plowing them back into the soil while they are still green. This process, known as Soil Reclamation, restores lost minerals and organic carbon Indian Economy, Nitin Singhania, Agriculture, p.306. In India, Sunhemp (Crotalaria juncea) and Dhaincha are the stars of green manuring. Sunhemp is particularly prized for its rapid growth and ability to fix atmospheric nitrogen, making it vital for reclaiming saline-alkaline soils before planting major crops like paddy.

Nutrient Source	Key Characteristics	Best For
Green Manure (Sunhemp/Dhaincha)	Adds biomass; fixes Nitrogen biologically.	Saline-alkaline soil reclamation.
Chemical Fertilizers (DAP/MoP)	Concentrated N, P, or K; fast-acting.	Intensive cropping; correcting acute deficiencies.
Fish Manure	Organic; contains 4-10% Nitrogen and 3-5% Phosphorus.	Quick-acting organic boost for all soil types.

Ultimately, the goal is to respect Pedogenesis (the natural process of soil formation) while ensuring the soil remains productive for future generations Indian Economy, Nitin Singhania, Agriculture, p.306. By integrating organic sources like fish meal and green manures with disciplined chemical use, farmers can maintain the soil's health and its ability to sustain life.

Sources: Indian Economy, Vivek Singh (7th ed. 2023-24), Subsidies, p.287-290; Geography of India, Majid Husain (9th ed.), Soils, p.8; Indian Economy, Nitin Singhania (2nd ed. 2021-22), Agriculture, p.306; Environment, Shankar IAS Academy (10th ed.), Agriculture, p.364

2. Classification of Organic Manures (basic)

To understand sustainable agriculture, we must first master how we nourish the soil. Organic manures are natural substances derived from plant and animal wastes. Unlike synthetic fertilizers that provide a 'quick fix' of chemicals, manures act as slow-release nutrients that improve the physical, chemical, and biological properties of the soil Shankar IAS Academy, Agriculture, p.363. We generally classify organic manures into two broad categories based on their volume and nutrient density: Bulky Organic Manures and Concentrated Organic Manures.

Bulky Organic Manures contain small percentages of nutrients but are applied in large quantities to improve soil structure and water-holding capacity. Common examples include Farmyard Manure (FYM), Compost (well-rotted organic matter), and Green Manure. Green manuring involves growing specific crops like Sunhemp (Crotalaria juncea) or Dhaincha and ploughing them back into the soil while they are still green to enhance nitrogen levels and organic carbon Majid Hussain, Environmental Degradation and Management, p.20. On the other hand, Concentrated Organic Manures are made from raw materials of animal or plant origin that are much richer in nutrients, such as oil cakes, bone meal, and blood meal.

Feature	Bulky Organic Manures	Concentrated Organic Manures
Nutrient Content	Low (Percentage-wise)	Relatively High
Quantity Applied	Large volumes (Tons/hectare)	Small volumes (kg/hectare)
Examples	FYM, Compost, Green Manure, Vermicompost	Oil cakes (Neem cake), Bone meal, Fish manure
Primary Benefit	Improves soil structure & humus	Direct supply of N, P, and K

An interesting distinction arises in how these are used across different farming systems. In Organic Farming, these manures are often processed externally (like vermicompost) and added to the field. However, in Natural Farming, the focus shifts toward encouraging the decomposition of organic matter right on the soil surface by microbes and earthworms, avoiding any external inputs altogether Vivek Singh, Agriculture - Part II, p.349.

Sources: Shankar IAS Academy, Agriculture, p.363-364; Majid Hussain, Environmental Degradation and Management, p.20; Vivek Singh, Agriculture - Part II, p.349

3. Sustainable Agriculture Policies in India (intermediate)

To understand sustainable agriculture in India, we must first look at the policy shift from the 'yield-at-any-cost' mindset of the Green Revolution to a focus on long-term ecological health and climate resilience. The primary vehicle for this change is the National Mission for Sustainable Agriculture (NMSA). Its goal is to make agriculture more productive and remunerative by promoting location-specific Integrated Farming Systems (IFS). By combining crops with livestock and forestry, the mission ensures that resources are conserved and used efficiently NCERT Class XII Geography, Land Resources and Agriculture, p.36.

Complementing this are schemes like the Paramparagat Krishi Vikas Yojana (PKVY), which specifically promotes organic farming through a cluster-based approach. A critical practical component of these sustainable policies is the encouragement of Green Manuring. This is the practice of growing nutrient-rich crops—such as Sunhemp (Crotalaria juncea) or Dhaincha—and plowing them back into the soil while they are still green. Sunhemp is especially valued in India because it is fast-growing, fixes atmospheric nitrogen, and helps in reclaiming saline or alkaline soils, making the land more fertile for subsequent crops like paddy Environment and Ecology (Majid Hussain), Environmental Degradation and Management, p.20.

Furthermore, sustainability extends to the livestock sector. The National Livestock Mission (NLM), launched in 2014-15, focuses on the quantitative and qualitative improvement of livestock production. This is vital because animals provide the organic manure necessary for sustainable crop cycles, while the mission ensures the availability of quality feed and fodder to keep the system self-sustaining Indian Economy (Vivek Singh), Agriculture - Part II, p.340.

Feature	Traditional Policy Focus	Sustainable Policy Focus (NMSA/PKVY)
Primary Goal	Maximizing immediate crop yield	Climate resilience & resource conservation
Soil Health	Heavy reliance on chemical NPK	Green manuring & Organic Carbon enhancement
System Type	Monocropping (Single crop)	Integrated Farming (Crops + Livestock)

Sources: INDIA PEOPLE AND ECONOMY, TEXTBOOK IN GEOGRAPHY FOR CLASS XII, Land Resources and Agriculture, p.36; Environment and Ecology (Majid Hussain), Environmental Degradation and Management, p.20; Indian Economy (Vivek Singh), Agriculture - Part II, p.340

4. Biological Nitrogen Fixation and Bio-fertilizers (intermediate)

Nitrogen is often called the 'limiting nutrient' in agriculture because, while it makes up 78% of our atmosphere, plants cannot 'breathe' it in. It is a fundamental building block of life, constituting about 16% of all proteins Environment, Shankar IAS Academy, Functions of an Ecosystem, p.19. For plants to use it, atmospheric nitrogen (N₂) must be 'fixed' or converted into reactive forms like ammonia (NH₃), nitrites (NO₂⁻), or nitrates (NO₃⁻).

Biological Nitrogen Fixation (BNF) is the natural process where specific microorganisms bridge this gap. These 'bio-factories' fall into two main categories:

• Free-living bacteria: Such as Azotobacter (which thrives in oxygen-rich soil) and Clostridium (which prefers anaerobic conditions).
• Symbiotic bacteria: The most famous is Rhizobium, which lives in a mutually beneficial relationship within the root nodules of leguminous plants like peas, beans, and lentils Science, Class VIII NCERT, The Invisible Living World, p.22. These bacteria trade fixed nitrogen for carbohydrates provided by the plant.

Once nitrogen is fixed into ammonia, a two-step process called nitrification usually follows: Nitrosomonas bacteria transform ammonia into nitrite, and then Nitrobacter converts that nitrite into nitrate, which is the form most easily absorbed by crops Environment, Shankar IAS Academy, Functions of an Ecosystem, p.20.

In sustainable farming, we harness this biology through Green Manuring. Instead of applying synthetic urea, farmers grow specific crops like Sunhemp (Crotalaria juncea) or Dhaincha (Sesbania aculeata). These plants are grown for a short period and then ploughed back into the soil while still green. This practice does more than just add nitrogen; it increases soil organic carbon and can even help reclaim saline-alkaline soils Environment and Ecology, Majid Hussain, Environmental Degradation and Management, p.20. It is a classic example of working with nature's chemistry rather than overriding it with chemicals.

Type of Organism	Examples	Role in Soil
Symbiotic Bacteria	Rhizobium	Fixes N₂ in legume root nodules.
Free-living Bacteria	Azotobacter	Fixes N₂ independently in the soil.
Nitrifying Bacteria	Nitrosomonas & Nitrobacter	Converts ammonia into usable nitrates.

Sources: Environment, Shankar IAS Academy, Functions of an Ecosystem, p.19-20; Science, Class VIII NCERT, The Invisible Living World, p.22; Environment and Ecology, Majid Hussain, Environmental Degradation and Management, p.20

5. Crop Rotation and Conservation Agriculture (intermediate)

To understand sustainable farming, we must first look at how we manage the soil's health over time. Crop Rotation is the practice of growing a series of different types of crops in the same area across a sequence of seasons. The logic is simple yet scientific: different plants have different "appetites" and "contributions." We categorize them into soil-exhaustive crops (like rice, wheat, and maize), which consume heavy amounts of nutrients, and soil-enriching crops (like pulses, peas, and gram), which fix atmospheric nitrogen back into the soil Environment and Ecology, Majid Hussain (3rd ed.), Environmental Degradation and Management, p.19.

When a farmer practices monoculture—growing only one crop like sugarcane or rice year after year—the soil loses specific nutrients and becomes structurally weak, leading to accelerated soil erosion. By contrast, Crop Diversification acts as a buffer, maintaining fertility and checking erosion Environment and Ecology, Majid Hussain (3rd ed.), Environmental Degradation and Management, p.20. Beyond just switching crops, we also use mulch crops (such as cowpea or groundnut) specifically to cover the soil and conserve its moisture Environment and Ecology, Majid Hussain (3rd ed.), Major Crops and Cropping Patterns in India, p.13.

Expanding on these ideas, Conservation Agriculture (CA) is a holistic management system. It isn't just about what you plant, but how you treat the ecosystem. CA aims to protect the soil from degradation and improve biodiversity while optimizing yields Indian Economy, Vivek Singh (7th ed.), Agriculture - Part II, p.352. It relies on three main pillars: minimal mechanical soil disturbance (no-till), permanent organic soil cover, and diversified crop rotations. This ensures that essential nutrient cycles, such as the Carbon and Nitrogen cycles, remain uninterrupted Environment, Shankar IAS Academy (10th ed.), Functions of an Ecosystem, p.17.

Feature	Monoculture	Crop Rotation / CA
Nutrient Status	Depletes specific nutrients rapidly.	Balances uptake and replenishment.
Soil Erosion	High; soil becomes vulnerable.	Low; soil structure is protected.
System Type	Exhaustive and linear.	Sustainable and regenerative.

Sources: Environment and Ecology, Majid Hussain (3rd ed.), Environmental Degradation and Management, p.19-20; Environment and Ecology, Majid Hussain (3rd ed.), Major Crops and Cropping Patterns in India, p.13; Indian Economy, Vivek Singh (7th ed.), Agriculture - Part II, p.352; Environment, Shankar IAS Academy (10th ed.), Functions of an Ecosystem, p.17

6. Concepts of Green Manuring (In-situ vs. Ex-situ) (exam-level)

Green manuring is one of the most effective and sustainable ways to "feed" the soil. Instead of relying solely on synthetic chemicals, farmers grow specific plants—usually legumes—and incorporate them back into the soil while they are still green. These plants act as a nutrient reservoir, releasing essential elements like Nitrogen, Phosphorus, and Potassium as they decompose Shankar IAS Academy, Agriculture, p.363. This practice is particularly vital in semi-arid regions where it helps conserve ground moisture and replenishes depleted nutrients GC Leong, Agriculture, p.244.

To master this topic for the exam, you must distinguish between the two primary methods of application: In-situ and Ex-situ (Green Leaf Manuring). While both aim to improve soil health, they differ in where the biomass is produced.

Feature	In-situ Green Manuring	Ex-situ (Green Leaf Manuring)
Method	Crops are grown and buried in the same field where the main crop will be planted.	Green leaves and twigs are collected from trees/shrubs elsewhere and brought to the field.
Common Crops	Sunhemp (Sani), Dhaincha, Cluster beans, and Cowpea Majid Hussain, Environmental Degradation and Management, p.20.	Glyricidia, Karanj (Pongamia), and Leucaena Shankar IAS Academy, Agriculture, p.364.
Best For	Reclaiming saline-alkaline soils and boosting organic carbon before paddy cultivation.	Farms where land is scarce or during seasons when a dedicated manure crop cannot be grown.

It is important to remember that green manure is distinct from compost. While green manure involves fresh plant material incorporated directly, compost is the result of a biological process where microorganisms decompose organic matter into a well-rotted, stable product with a lower C:N (Carbon-to-Nitrogen) ratio Shankar IAS Academy, Agriculture, p.364. In India, Sunhemp is a superstar of in-situ manuring because it grows rapidly, fixes atmospheric nitrogen, and produces massive amounts of biomass that transform soil structure.

Sources: Shankar IAS Academy, Agriculture, p.363-364; Majid Hussain, Environmental Degradation and Management, p.20; GC Leong, Agriculture, p.244

7. Major Green Manure Crops in India (exam-level)

Green manuring is a time-tested, sustainable agricultural practice often described as "growing your own fertilizer." It involves the cultivation of specific fast-growing plants—primarily legumes—which are plowed back into the soil while still green and succulent. This process enhances soil organic carbon, improves soil structure, and naturally fixes atmospheric nitrogen through root nodules, reducing the dependency on chemical urea Environment and Ecology, Majid Hussain, Environmental Degradation and Management, p.20. In the Indian context, the most prominent green manure crop is Sunhemp (Crotalaria juncea). It is a powerhouse of biomass and is particularly celebrated for its ability to reclaim saline-alkaline soils, which are otherwise difficult to cultivate. Farmers often grow Sunhemp just before the monsoon to prepare the land for paddy (rice) transplantation. Interestingly, Sunhemp is also a multi-purpose crop; its hardy fibers are utilized in making ropes (cordage) and high-quality bleachable pulp for paper manufacturing Environment and Ecology, Majid Hussain, Major Crops and Cropping Patterns in India, p.52. While Sunhemp is a versatile all-rounder, Indian agriculture utilizes a variety of other crops based on regional soil and climate conditions. These are broadly categorized into two types:

Type	Mechanism	Key Examples
In-Situ Green Manuring	The crop is grown and buried in the same field.	Dhaincha (Sesbania), Cluster beans (Guar), Cowpea, Berseem, and Sunhemp.
Green Leaf Manuring	Leaves and twigs are collected from wasteland or forest trees and added to the field.	Glyricidia, Karanj (Pongamia), and Leucaena Environment, Shankar IAS Academy, Agriculture, p.364.

Beyond nutrient enrichment, these crops serve as a vital tool for soil conservation. By providing a thick canopy cover, they protect the topsoil from the erosive force of rain and wind, thereby preventing land degradation Environment and Ecology, Majid Hussain, Environmental Degradation and Management, p.20.

Sources: Environment and Ecology, Majid Hussain (Access publishing 3rd ed.), Environmental Degradation and Management, p.20; Environment and Ecology, Majid Hussain (Access publishing 3rd ed.), Major Crops and Cropping Patterns in India, p.52; Environment, Shankar IAS Academy (10th ed.), Agriculture, p.364; Geography of India, Majid Husain (McGrawHill 9th ed.), Soils, p.24

8. Solving the Original PYQ (exam-level)

Now that you have mastered the concepts of soil fertility and nitrogen fixation, this question asks you to apply that knowledge to practical Indian agriculture. Green manuring is the process of growing specific plants and plowing them back into the soil while they are still green to enhance organic matter and nutrients. To identify the correct plant, you must look for a leguminous species that is fast-growing and capable of producing high biomass. This practice bridges the gap between biological cycles and sustainable farming yields.

When reasoning through the choices, Sunhemp (Crotalaria juncea) is the clear winner because it fulfills all the criteria of an ideal green manure crop. As a legume, it fixes atmospheric nitrogen, and its rapid growth allows it to be incorporated into the soil just before the main crop is sown. According to Environment and Ecology, Majid Hussain, Sunhemp is particularly valued in India for reclaiming saline-alkaline soils and is frequently grown before rice transplantation to provide a natural nitrogen boost. You should also keep Dhaincha and cluster beans in mind as other common alternatives used in similar contexts.

UPSC often uses familiarity traps by listing major crops like Wheat, Rice, and Cotton. While these are central to Indian agriculture, they are nutrient-exhaustive crops—they take nutrients out of the soil rather than putting them back in. Remember the distinction: wheat and rice are the 'consumers' that benefit from the 'contribution' made by green manures like Sunhemp. In the exam, always look for the plant that serves as the soil builder rather than the primary harvest crop.