Green manure- role in crop production: Definition, objectives types of green manuring, desirable characteristics, advantages and limitations of green manuring.

B. Sc. Agriculture (Hons.) Ist. Semester (Six Deam Commitee of ICAR)

Definition

Green manuring is the practice of growing, ploughing under, and mixing green plant material into the soil to enrich it with organic matter and nutrients.
The plants used for this purpose are called green manure crops.

According to FAO:

“Green manuring is the practice of turning into the soil undecomposed green plant tissues for the purpose of improving soil fertility and physical condition.”
Key Idea: Green manuring helps in adding organic matter, fixing atmospheric nitrogen (through legumes), improving soil structure, and promoting soil microbial activity.

The main objectives are:

To increase soil fertility by adding organic matter and essential nutrients.
To improve soil physical properties such as aggregation, aeration, and porosity.
To enhance soil biological activity, promoting beneficial microbes.
To add nitrogen to the soil through biological nitrogen fixation (in leguminous crops).
To prevent soil erosion and nutrient loss by maintaining soil cover.
To improve water infiltration and moisture-holding capacity of soil.
To reduce dependence on costly chemical fertilizers.
To suppress weeds and improve soil health in a sustainable manner.

Green manuring is classified into two major types:

a) In-situ Green Manuring

In this method, green manure crops are grown and incorporated into the same field where their effect is desired.
Common in paddy (rice) fields before transplanting.

Common crops used:

Features:

b) Ex-situ or Green Leaf Manuring

Green leaves and tender twigs of trees, shrubs, or hedgerow plants are collected from other places and incorporated into the soil of cultivated fields.
Common in regions where space or time does not permit in-situ green manuring.

Common sources:

Features:

An ideal green manure crop should possess the following characteristics:

Fast-growing and capable of producing abundant green biomass in a short period.
Leguminous nature with high nitrogen-fixing ability through Rhizobium symbiosis.
Deep and spreading root system to absorb nutrients from lower soil layers.
High organic matter and nutrient content, especially nitrogen.
Adaptable to local soil and climatic conditions.
Easy to establish and quickly decomposable after incorporation.
Non-competitive with main crops for moisture and nutrients.
Tolerant to drought, salinity, or waterlogging, depending on region.
Should not serve as host for pests and diseases of main crops.
Ability to improve soil texture and microbial population effectively.

5. Advantages of Green Manuring

Improves soil fertility through addition of organic matter and nutrients.
Adds biologically fixed nitrogen to the soil (20–200 kg N/ha depending on species).
Improves soil structure and aeration.
Reduces soil erosion and nutrient losses.
Stimulates soil microbial activity and promotes beneficial soil fauna.
Improves nutrient-use efficiency of applied fertilizers.
Enhances water-holding capacity and infiltration.
Reduces weed infestation by shading and competition.
Saves cost of chemical fertilizers and promotes eco-friendly agriculture.
Improves crop yields sustainably.

6. Limitations of Green Manuring

Requires land and time, which may not be available in intensive cropping systems.
Competition for water in dryland areas.
Increased cost of seed and incorporation.
Slow decomposition in low temperature or dry conditions.
Temporary nitrogen immobilization may occur during decomposition.
Unsuitable for short-duration crops or regions with limited rainfall.
Limited adoption due to lack of awareness and availability of green manure seeds.

Common Green Manure Crops and Nitrogen Contribution

Welcome to