Green Manure and Cover Cropping: Benefits for Soil Health

Table of Contents

Introduction

After harvesting a crop, many farmers prepare their fields for the next planting season. However, leaving the soil bare for several weeks or months can expose it to erosion, weed growth, and nutrient loss. During this period, the soil may receive little protection from rain, wind, or intense sunlight.

Green manure and cover cropping offer a practical way to keep agricultural land productive even when the main crop is not growing.

Instead of leaving a field empty, farmers grow selected plants to protect the soil, add organic matter, recycle nutrients, or improve conditions for the next crop. Some of these plants are later incorporated into the soil, while others are cut and left on the surface.

These practices are useful in many farming systems, from small vegetable gardens to larger crop fields. Their success, however, depends on selecting suitable plants, understanding local growing conditions, and managing the cover crop before the next main crop is planted.

What Is Green Manure?

Green manure is a crop grown mainly to improve soil fertility and soil condition rather than to produce grain, fruit, or vegetables for sale.

Farmers usually cut or incorporate the green plant material into the soil while it is still relatively young. As the leaves, stems, and roots decompose, they contribute organic matter and release nutrients that can become available to future crops.

Leguminous green manure crops are particularly useful because they can form a partnership with nitrogen-fixing bacteria in their root nodules. These bacteria convert atmospheric nitrogen into forms that the plant can use. Some of this nitrogen may eventually become available to the following crop when the plant residues decompose.

Common examples include:

Dhaincha (Sesbania), often used in rice-based farming systems.
Sunn hemp, a fast-growing legume used in suitable warm climates.
Cowpea, which can provide soil cover and contribute nitrogen.
Certain clovers and field peas, where local climate and cropping systems are suitable.

Green manure does not produce an instant supply of fertilizer. The nutrients contained in plant material must first be released through decomposition, and the amount available to the next crop depends on the species, biomass, soil conditions, and timing of incorporation.

What Is Cover Cropping?

Cover cropping is the practice of growing plants primarily to protect and improve agricultural soil between, before, or sometimes alongside main crops.

A cover crop may be planted after harvesting a cereal crop, during a gap between vegetable crops, or in an orchard where the ground would otherwise remain bare.

Unlike green manure, cover crops do not always need to be incorporated into the soil. Farmers may cut them and leave the residues on the surface as mulch. Some cover crops can also be grazed or harvested, depending on the management system and the farmer’s objectives.

Cover crops are selected for different purposes. A legume may help add nitrogen, while a grass may produce a large amount of protective residue. Other species can help capture nutrients left in the soil or provide living roots that support soil structure.

In practice, green manure and cover cropping overlap. A crop grown to cover the soil and later incorporated as green manure is also a cover crop.

Green Manure vs. Cover Cropping: What Is the Difference?

The main difference is the purpose and management of the plants.

Feature	Green manure	Cover cropping
Main purpose	Add organic material and support soil fertility	Protect and improve soil between or alongside main crops
How plants are managed	Commonly cut and incorporated into the soil	May be incorporated, mowed, grazed, or left as surface residue
Nitrogen contribution	Legumes can contribute nitrogen through fixation	Depends on the cover crop species; legumes may fix nitrogen
Soil protection	Protects soil while growing and can add residue	Often specifically managed for erosion protection, weed suppression, and soil cover
Examples	Dhaincha, sunn hemp, suitable clovers	Cowpea, oats, rye, clovers, and locally adapted mixtures

The same plant can serve both purposes. For example, a farmer may grow cowpea to protect the soil during a fallow period and then incorporate its young growth before planting vegetables.

Benefits of Green Manure and Cover Cropping

1. Improve soil fertility

Green manure crops add plant residues to the soil. As microorganisms break down this material, nutrients are gradually released.

Legumes can also contribute nitrogen through biological nitrogen fixation. The actual amount depends on successful crop establishment, suitable bacterial activity, growing conditions, and how the residues are managed.

Farmers should not assume that every green manure crop will replace a fixed amount of fertilizer. Soil testing and crop nutrient requirements remain important.

2. Add organic matter

Plant roots, leaves, and stems contribute organic material to the soil.

Over time, regular additions of crop residues can support soil organic matter and biological activity. This can help improve the soil’s ability to form stable aggregates and maintain a favourable growing environment for roots.

The results develop over time. A single cover crop season will not necessarily transform a degraded field.

3. Reduce soil erosion

Bare soil can be vulnerable to heavy rainfall and wind. Cover crops protect the soil surface with their leaves and residues, while their roots help hold soil particles in place.

This protection can be especially valuable on sloping fields, exposed land, and farms that experience intense rainfall.

4. Help suppress weeds

A well-established cover crop can compete with weeds for light, space, water, and nutrients. Dense growth may reduce the opportunity for some weeds to establish.

When cover crop residues remain on the soil surface, they can also block light and make weed emergence more difficult.

However, cover crops are not a complete replacement for weed management. Poorly established stands may leave gaps, and a cover crop allowed to produce unwanted seed can become a weed problem itself.

5. Support soil structure and water movement

Different cover crops develop different root systems. Their roots can create channels, contribute organic matter, and support soil aggregation.

These effects may improve water infiltration and help soil resist surface crusting. The degree of improvement depends on soil type, root growth, traffic, and the wider farming system.

6. Capture and recycle nutrients

Some cover crops take up nutrients remaining in the soil after the main crop has been harvested.

For example, grasses can capture available nitrogen and hold it in their plant tissues. When the cover crop is later terminated and decomposes, some of those nutrients can return to the soil.

This nutrient recycling can help reduce losses, but it does not mean that every nutrient will be available to the next crop at the right time.

Types of Cover Crops and Green Manure Plants

The most suitable crop depends on the farmer’s goal, climate, soil, available growing period, and the next crop in the rotation.

Legumes

Legumes include plants such as cowpea, sunn hemp, dhaincha, clover, and field peas.

They are commonly chosen when farmers want to contribute nitrogen, produce green biomass, or provide ground cover.

Legumes rely on compatible bacteria to fix nitrogen. In fields where a suitable legume has not been grown recently, farmers may need to consider appropriate inoculation advice from a local agricultural specialist.

Grasses and cereal crops

Oats, rye, and other suitable cereal grasses are often used for soil cover, erosion protection, and nutrient capture.

They can produce substantial root and shoot biomass. Their residues may persist on the surface longer than young legume residues.

One management concern is that mature, carbon-rich grass residues can temporarily tie up some soil nitrogen during decomposition. This may affect the following crop if residue management and nutrient planning are not appropriate.

Brassicas and other broadleaf crops

Certain brassicas, including mustard, radish, and turnip, are used as cover crops in suitable regions.

Their rapid growth can help establish soil cover, and some species develop substantial roots. Their performance depends on local temperature, moisture, planting dates, and crop rotation.

Farmers should also consider whether a cover crop could host pests or diseases that affect the following main crop.

Cover crop mixtures

Some farmers grow two or more species together to combine different functions.

For example, a legume and a grass may provide a mix of nitrogen fixation, biomass production, and soil cover. However, mixtures require careful planning because species may compete with one another, and seed costs and termination requirements can increase.

For beginners, a single well-adapted cover crop may be easier to manage than a complex mixture.

How to Grow Green Manure and Cover Crops

Step 1: Decide what you want to improve

Before selecting seeds, identify the main problem or goal.

Are you trying to protect soil from erosion, improve organic matter, contribute nitrogen, suppress weeds, or cover the land between two crops?

The answer will guide your crop selection. A species chosen for nitrogen fixation may not produce the same amount of surface residue as a cereal grass.

Step 2: Choose a crop suited to your farm

Consider the local climate, soil type, available moisture, planting window, and the crop you intend to grow next.

In warm regions of India, farmers may consider dhaincha, sunn hemp, or cowpea where these crops fit the local rotation. In cooler periods, oats or suitable legumes may be options.

These are examples, not universal recommendations. Consult local agricultural extension guidance for suitable varieties and sowing dates.

Step 3: Prepare the seedbed and sow

A cover crop needs good seed-to-soil contact to establish successfully.

Depending on the species and farm equipment, seeds may be drilled or broadcast. After broadcasting, light incorporation or another suitable method can improve contact between seeds and moist soil.

Use the locally recommended seed rate and planting depth. Avoid sowing into soil that is too dry for reliable germination unless irrigation or expected rainfall can support establishment.

Step 4: Manage growth and moisture

Monitor the field for poor establishment, weeds, pests, and moisture stress.

A cover crop is still a growing plant and uses water. In regions where rainfall is limited, it may compete with the following main crop if allowed to grow too long.

Farmers should balance the benefits of additional biomass against the need to conserve water for the next crop.

Step 5: Terminate the cover crop at the right time

Termination means stopping the cover crop’s growth before it interferes with the next crop.

Possible methods include mowing, cutting, rolling, suitable tillage, or other locally appropriate techniques. The correct method depends on the species, growth stage, equipment, and farming system.

Green manure is often incorporated while the plants are young and before they produce mature seed. Cover crops managed as surface mulch may instead be cut or rolled and left on the soil.

The timing matters. Excessive growth can make residue difficult to manage, while late termination may increase competition for water or nutrients.

Step 6: Allow residue to decompose when needed

When green manure is incorporated, the farmer should allow sufficient time for decomposition before planting the next crop.

A waiting period of around two to three weeks is sometimes used as a general starting point, but it is not a universal rule. The appropriate interval varies with the plant species, amount of biomass, soil temperature, moisture, and next crop.

Where possible, follow local recommendations and avoid planting into residue that could interfere with seed placement or early crop establishment.

A Practical Example: Using Green Manure Between Two Crops

Imagine a farmer harvesting a cereal crop and preparing the field for a vegetable crop.

Rather than leaving the land bare, the farmer could consider growing a suitable short-duration legume during the available gap.

The process might look like this:

Harvest the main crop and assess soil moisture.
Select a locally adapted legume that fits the available growing period.
Establish the green manure crop using suitable seed and planting practices.
Monitor its growth and terminate it before it becomes difficult to manage or produces unwanted seed.
Incorporate the plant material where appropriate and allow decomposition.
Prepare the field for the next vegetable crop, using soil testing and nutrient recommendations to guide fertilizer decisions.

This example illustrates the principle, not a fixed calendar. The actual sequence will depend on the region, rainfall, crop varieties, and the time required by the next crop.

Challenges Farmers Should Consider

Green manure and cover cropping can offer valuable benefits, but they also involve costs and management decisions.

Water competition: A cover crop may use moisture needed by the next crop, especially in dry areas.

Seed and establishment costs: Seed, labour, irrigation, and equipment can add costs. A cover crop that fails to establish may provide limited benefit.

Residue management: Dense plant material can complicate tillage, planting, or crop emergence. Some residues may temporarily reduce nitrogen availability.

Pest and disease risks: Certain cover crops can host pests or pathogens that affect the following crop. Crop rotation and species selection should take these risks into account.

Timing: A cover crop must be terminated at an appropriate stage. Allowing it to produce unwanted seed may create future weed problems.

For these reasons, farmers should begin with a manageable crop and a clear objective. Small trials can help determine whether a particular cover crop works under local conditions before adopting it across the entire farm.

FQAs.

Q1. Is green manure the same as compost?

No. Green manure is plant material grown in the field and then managed to improve soil. Compost is organic material that has been decomposed through a managed process before application.

Both can contribute organic matter, but their nutrient availability and management requirements differ.

Q2. Do cover crops always increase crop yields?

No. Cover crops can improve soil conditions and nutrient cycling, but the outcome depends on species selection, weather, management, and the following crop. Poor timing or excessive competition can reduce the performance of the main crop.

Q3. Can green manure replace chemical fertilizers?

Green manure can contribute nutrients, especially nitrogen when legumes are used. However, it does not automatically supply all the nutrients required by a crop. Farmers should use soil testing and suitable nutrient recommendations rather than assume that fertilizer is no longer needed.

Q4. Can cover crops be grown in dry regions?

Yes, but selection and timing are especially important. Farmers in dry regions should consider short-duration species, available rainfall, soil moisture, and whether the cover crop could reduce water available for the next crop.

Q5. Should green manure always be ploughed into the soil?

No. Incorporation is one management option, but some cover crops can be cut and left as surface residue. The suitable approach depends on the farming system, the crop’s growth stage, and the next planting operation.

Conclusion

Green manure and cover cropping are useful ways to make better use of the time between main crops. They can protect the soil, contribute organic matter, support nutrient cycling, and help manage weeds.

Their benefits are strongest when the farmer chooses a suitable species, establishes it successfully, and manages its termination carefully.

Rather than treating cover crops as a guaranteed solution, farmers should view them as one part of a wider soil-management plan that includes crop rotation, appropriate nutrient management, water conservation, and regular field observation.

Related reading: Explore our guide to Regenerative Farming to learn how soil-cover practices can fit into a broader approach to sustainable agriculture.

Green Manure and Cover Cropping: Benefits, Types, and How to Use Them in Farming