Green manure refers to material that has not yet decomposed and is utilized as manure. There are two ways to get it: either by planting green manure crops or by gathering green leaves and twigs from plants growing in wastelands, field bunds, and forests. Green manuring is the process of growing plants in the field, mainly members of the leguminous family, and incorporating them into the soil once they have grown sufficiently. The sunn hemp, dhaincha, pillipesara, cluster beans, and Sesbania rostrata plants are the most significant green manure crops. The concept of green manuring is quickly gaining popularity in organic farming, where it contributes significantly to a system of sustainable yearly cropping. This article will explain to you about Green Manuring which will be helpful in preparing the Agriculture Syllabus for the UPSC Civil Service exam.

What is Green Manuring?

• Green manuring is the practice of ploughing or turning into the soil undecomposed green plant tissues in order to improve soil physical structure and fertility.
• Green manuring is the primary supplementary method of adding organic matter to the soil where possible.
• Green manure crops provide organic matter as well as additional nitrogen, especially if they are legumes, due to their ability to fix nitrogen from the air with the help of root nodule bacteria.
• Green manure crops also act as a barrier against erosion and leaching.
• Green manure should be incorporated into the soil prior to flowering because it is grown for its green leafy material, which is high in nutrients and protects the soil.
• Green manures will not break down quickly in the soil, but will gradually add nutrients to the soil for the next crop.

Green Manuring - Types

Green Manuring in Situ (Leguminous Green Manures)

• The leaves, stems, and roots of leguminous green manures are particularly rich in nitrogen because legumes fix their nitrogen.
• These crops are produced on farms and, when they are about to flower, are finally ploughed under and buried in the same soil.
• It is a method of growing green manure crops and incorporating them into the soil of the same field that will be green manured, either as a pure crop or as an intercrop with the main crop.
• Sunn hemp, mung beans, black gram, cluster beans, pigeon peas, chickpeas, fenugreek, green peas, soybean, and cowpeas are a few examples of leguminous green manure crops.

Green Leaf Manuring

• It is a method of collecting green plant tissues from other locations.
• It refers to incorporating green leaves and tender green twigs collected from outside the field into the soil to be green manured.
• Some leaves of leguminous trees, rather than the entire plant, are employed as green manures. Trees are gathered for their leaves.
• Tree leaves are gathered and combined with soil when they are still fresh. Nitrogen is gradually released into the soil via green leaf manures.
• Gliricidia, Leucaena, Sesbania, and Pongamia are a few examples of green leaf manures.

*To know more about the topic, click this link Green Leaf Manuring

Cover Crops

• To manage weeds and stop soil erosion, the entire farmland is planted with mostly non-leguminous plants.
• Cover crops with green manure serve as "a living mulch."
• Brassica, millets, oats, rye, and radish are some varieties of cover crops.

Green Manuring - Features of Suitable Plants

• In general, the best green manure plants ought to be:
• simple to plants;
• simple to establish;
• rapidly produce succulent tops and roots;
• rapidly create a good ground cove;r and
• be able to grow on unfavorable soils.
• Due to the soil's increased nitrogen content, it is better to sow a legume than a non-legume.
• However, in general, the legume seed is larger, it is more challenging to grow, and the crop may be so important as animal feed that one would not want to turn the stand under.
• Some of the crops can't grow in particular soil types or climate zones, while other crops are too valuable to be used as haylage while still in their early stages.
• Growing two crops together has several benefits for green manuring.
• Both crops may benefit from the connection if they are suitable to each other, the soil, and the climate.
• A crop may provide the other with tangible assistance. The fixed nitrogen may help the other if one is a legume.
• Oats & peas and rye & vetch are two excellent examples of mixtures for green manure.
• Although companion planting is not a new practice, it is now the subject of greater research.

Green Manuring - Nutrient Release

• By consuming organic debris, heterotrophic bacteria that break down green manure converts it into plant nutrients.
• Similar to making compost fertilizer, this process is aided by warmth and moisture.
• Large volumes of carbon dioxide and weak acids are released by the plant matter, and these substances react with the insoluble soil minerals to release helpful nutrients.
• For example, adding green manure to soils rich in calcium minerals can increase the amount of phosphate in the soil, which serves as a fertilizer.

Green Manuring - Carbon to Nitrogen Ratio

• The ratio of carbon to nitrogen in a plant is an important consideration because, if the incorrect plants are used to generate green manure, it will affect the soil's nutrient content and could deprive a crop of nitrogen.
• Depending on the age of the plant and the species, the carbon-to-nitrogen ratio will vary.
• The ratio must be less than 30:1 to avoid the manure bacteria from diminishing the soil's current nitrogen.
• The value of nitrogen is always one, whereas the value of carbon or carbohydrates is stated as a value ranging from around 10 to 90.
• Rhizobium is a soil organism that works with green manure to keep nitrogen from the atmosphere in the soil.
• Due to their rhizobium-rich root systems, legumes like beans, alfalfa, clover, and lupines are frequently chosen as the preferred source of green manure material.

Green Manuring - Advantages

• Enhances the Organic Matter: According to experts, it increases the amount of organic matter in the soil, fills any nutritional gaps, minimizes the need for inorganic fertilizers, etc.
• Good Alternative to Organic Manure: It is a good substitute for organic manure and stabilizes the soil's structure while preserving nutrients and adding nitrogen.
• Rapid Decomposition Process: Large amounts of carbon dioxide and weak acids are released during its quick decomposition, and these substances act on insoluble soil minerals to release nutrients for plant growth.
• Dry Matter: It includes 15 to 18 quintals of dry matter per acre, along with 20 to 40 kg of nitrogen and other elements including phosphorus, potassium, zinc, copper, iron, and manganese.
• Suppress Weed Growth: Green manure crops are chosen by farmers because they naturally inhibit weed growth.
• Topsoil Stability and Reduced Soil Erosion: By adding porosity and aeration to the soil, it serves to improve soil structure, aeration, permeability, and infiltration capacity. It also reduces soil loss from runoff and erosion.
• It changes the soil's physical, chemical, and biological environments by increasing the organic matter regime. Indeed, this increases the activity of soil microorganisms.
• Green manure crops aid in the return of various plant nutrients from the subsurface soil layer to the surface soil layer.
• Green manuring can improve and restore nutrient regimes that would otherwise be lost due to leaching.
• Green manure crops have a residual effect on the supply of various plant nutrients, which aids in the growth of the next crop.

Green Manuring - Disadvantages

• Nutrient Pollution: The over-fixation of nitrogen and phosphorus into the soil, which makes it poisonous and further contributes to nutrient pollution, can occasionally result from the excessive use of green manure.
• Expensive: Farmers may decide to grow less cultivated crops in order to plant green manure crops because they will likely find them to be prohibitively expensive.
• Impact on Marketable Cash Crop: During the manure period, farmers are unable to plant their marketable cash crop since they occasionally prefer to improve soil fertility to plant crops.
• Impacts the Primary Source of Income: There may be instances when the green manure crop competes with the crops that will serve as the main source of income.
• Under rainfed conditions with limited rainfall, proper decomposition of green manure crops may not occur, and thus the benefits of green manuring may not be realized satisfactorily.
• When the cost of green manuring crops exceeds the cost of chemical nitrogenous fertilizers, green manuring may not be cost-effective.
• The occurrence of diseases and insects in field crops is changing.
• Due to the decomposition of green manure crops, various toxic substances such as organic acids such as butyric acid, propionic acid, and others, as well as toxic gases such as methane (CH4) and others, are liberated, which affects the root growth of growing plants and thus affects growth and yield by inhibiting nutrient absorption by the plant.

Conclusion

Farmers in India have known the benefits of green manure for thousands of years, as documented in texts like the Vrikshayurveda. However, limitations in the usage of green manure should be taken into account, including the time, effort, and resources necessary to successfully cultivate and utilize these cover crops. To guarantee effective growth and usage of the cover crop, it is crucial to select green manure crops based on the growing location and yearly precipitation quantities.

FAQs

Q1: What is green manuring?

Q2: What are the benefits of green manuring?

Q3: Which crops are commonly used for green manuring?

Q4: How does green manuring affect soil health?

Q5: When is the best time to incorporate green manures into the soil?

MCQs

1. What is the primary purpose of green manuring?

a) Pest control

b) Soil fertility improvement

c) Water conservation

d) Crop harvesting

2. Which of the following crops is NOT typically used for green manuring?

a) Cowpea

b) Mung bean

c) Wheat

d) Gram

3. How does green manuring help in weed management?

a) By using pesticides

b) By smothering weeds

c) By reducing soil moisture

d) By increasing sunlight exposure

4. What is the ideal time to incorporate green manures into the soil?

a) During monsoon

b) Before sowing the main crop

c) After harvesting

d) Mid-season

5. Which nutrient is primarily added to the soil through leguminous green manures?

a) Phosphorus

b) Nitrogen

c) Potassium

d) Calcium

GS Mains Questions and Model Answers

Q1: Discuss the role of green manuring in sustainable agriculture.

Answer: Green manuring is vital for sustainable agriculture as it enhances soil fertility without chemical inputs. This practice improves soil structure and water retention while reducing erosion. By incorporating legumes, farmers benefit from nitrogen fixation, which replenishes soil nutrients essential for subsequent crops. Green manuring also aids in controlling weeds and pests, thereby minimizing the need for herbicides and pesticides. Furthermore, it contributes to carbon sequestration, promoting environmental sustainability. Overall, green manuring serves as an eco-friendly approach to enhance agricultural productivity while safeguarding the ecosystem.

Q2: Analyze the benefits and challenges of implementing green manuring in Indian agriculture.

Answer: Green manuring offers numerous benefits in Indian agriculture, such as improving soil fertility, enhancing microbial activity, and promoting sustainable farming practices. By using local leguminous crops, farmers can significantly reduce the need for chemical fertilizers, leading to cost savings and healthier soils. However, challenges include the need for proper knowledge and training among farmers regarding the best practices for green manuring. Limited access to seeds of suitable green manure crops and climatic variations can also hinder effective implementation. Addressing these challenges through education and support can enhance the adoption of green manuring practices in India.

Q3: Evaluate the impact of green manuring on crop yield and soil health.

Answer: Green manuring positively impacts both crop yield and soil health. By adding organic matter to the soil, it improves soil structure and aeration, facilitating better root growth and nutrient uptake for subsequent crops. Studies show that fields enriched with green manure exhibit higher crop yields compared to those relying solely on chemical fertilizers. Additionally, the practice enhances soil microbial activity, leading to improved nutrient cycling and availability. Over time, consistent green manuring practices can restore degraded soils and maintain long-term agricultural productivity, thus contributing to food security.

Previous Year Questions on  Green Manuring

1. UPSC CSE 2018

Question: "What are the advantages of green manuring in Indian agriculture?"

Answer: Green manuring provides several advantages in Indian agriculture, primarily enhancing soil fertility and structure. By incorporating organic matter, it improves water retention and nutrient availability, crucial for the growth of subsequent crops. Green manuring reduces dependency on chemical fertilizers, thereby lowering costs for farmers and promoting a healthier ecosystem. It also aids in pest management and weed suppression, resulting in a more sustainable farming practice. Additionally, the practice contributes to carbon sequestration, helping mitigate climate change effects. Overall, green manuring fosters a balanced agro-ecosystem while supporting food security.

2. UPSC CSE 2020

Question: "Examine the challenges faced in adopting green manuring practices among Indian farmers."

Answer: The adoption of green manuring practices among Indian farmers faces several challenges, primarily due to lack of awareness and knowledge regarding the benefits and methods. Many farmers rely heavily on chemical fertilizers for immediate results, thus undervaluing organic practices. Access to quality seeds of suitable green manure crops is often limited, particularly in remote areas. Additionally, climatic variations and inadequate infrastructure for crop rotation can hinder effective implementation. Economic constraints also play a role, as farmers may perceive green manuring as an additional cost rather than a long-term investment. Addressing these challenges through education, training, and providing necessary resources is essential for promoting green manuring in India.