Sustainable Agriculture Extension Manual

Mulching

Mulch is dry, vegetative material used to cover the soil. It helps reduce evaporation and retain moisture, reduce soil erosion, and provide plant nutrients as the material decomposes.

Location

Mulch can be used in fields before and after planting, as well as around young crop plants. It is especially useful for high-valuable vegetable crops, and for for growing crops in dry areas, during dry-season cropping, and in places where the soil is easily eroded by heavy rains.

Advantages

Mulch keeps the soil underneath moist longer than bare soil.
It controls soil erosion by cushioning the impact of raindrops and by slowing runoff.
It suppresses weeds by shading them out.
It leads to healthy crop growth.

Disadvantages

Mulching is labour-intensive.
It can introduce new pests and diseases into a field.
Dead plants for use as mulch may not be available.

Requirements

Dry plant materials you can find nearby, such as grass, maize or sorghum stalks, maize husks, wheat straw.

Procedure

1. Carry to the field the material you want to spread as mulch.

2. Spread it on the soil using your hands or a rake. Put a layer of mulch 7-15 cm (3-6 inches) deep all over the bed, or around the growing plants. Do not put on so much mulch that you bury the plants or shade them out.

Do's

Use dry plant material that does not rot quickly.

Dont's

Don't use wet or green material as mulch.

Green manuring

Green manures are fast-growing plants (legumes and non-legumes) planted on a piece of land to improve soil fertility and protect the soil from erosion. They are normally low, spreading plants that grow fast and cover the soil surface quickly after planting. During or after the growing season, the green-manure plants are slashed and incorporated into the soil, where they decompose, releasing nutrients and improving the soil structure.

Green manures conserve and improve the soil in several ways:

Legumes such as soybeans, green gram, groundnuts and pigeonpeas take nitrogen from the air and fix it in a form they can use. This nitrogen-fixing is done by tiny micro-organisms called bacteria living in the lumps (called nodules) on the roots of the legumes. The roots of other plants (such as maize) growing close by can also absorb some of the nitrogen. When the legume dies and rots, the nitrogen in its leaves, stem and roots is released into the soil, where other plants can absorb it. The rotting plants also increase the amount of organic matter in the soil.
Green-manure crops prevent the soil from being washed away by rainwater. If a raindrop hits bare soil, the splash dislodges tiny soil particles, which can be washed away easily. The impact of the raindrop also compacts the surface, making it harder for the rainwater to seep into the soil. Instead of seeping in, the water runs off the surface, carrying with it the dislodged particles. On even gentle slopes, this can cause gullying. The green manure acts as a cover crop: it breaks the fall of raindrops, so preventing compaction and helping the water seep in rather than running off. Its roots bind the soil and stop running water from eroding it.

Examples of green-manure crops

Food legumes Fodder legumes Others

Bambara groundnut (Voandzeia subterranea)
Clover (Trifolium sp.) Pumpkins (Cucurbita sp.)

Chickpea (Cicer arietinum) Lablab bean (Dolichos lablab)

Sweet potato (Ipomoea batatas)

Cowpea (Vigna sinensis)
Lucerne (alfalfa, Medicago sativa) Kikuyu grass (Pennisetum clandestinum)

Green gram (Phaseolus aureus)
Lupin (Lupinus sp.)

Groundnut (Arachis hypogaea)
Seratro

Lablab bean (Dolichos lablab)
Stylo (Stylothanses sp.)

Pigeonpea (Cajanus cajan)

Sunn hemp (Crotalaria juncea) (fibre)

Velvetbean (Mucuna deeringiana)

Vetch (Vicia sp.)

The green-manure crop protects the soil from the direct heat of the sun, helping it retain moisture. It breaks the wind and stops soil particles from being blown away.

The green-manure crop can be grown as a pure stand, so it enriches the soil for a cereal crop grown in the next season. It can also be grown as an intercrop between rows of another main crop, such as maize, sorghum and millet, or beneath fruit trees.

Location

Green manuring can be used in various types of soils. It is especially appropriate for infertile soils and areas with low rainfall, where artificial fertilizer cannot be used effectively because of the lack of moisture. It is useful on sandy soils, as deep-rooted legumes help recycle nutrients. It also helps improve the structure of heavy soils. It can help control erosion in hilly areas or places with strong winds.

Green manuring in Rachuonyo District, Kenya
In 1994, the NGO Community Mobilization Against Desertification (C-MAD) and Loyce Tula, a farmer in Rachuonyo District in western Kenya, decided to test green manuring on Loyce's farm. That year, Loyce used compost to fertilize her fields, but harvested a somewhat disappointing yield of only 2.5 sacks of maize from a plot measuring 16 x 30 m (a yield of 4.5t/ha).
In 1995, Loyce inter-cropped her maize with double rows of beans. The plot yielded 4.5 sacks (8.4 t/ha) of maize, and 2 sacks (3.7 t/ha) of beans. The following year, she planted a pure stand of maize, and harvested 5 sacks (9 t/ha). That year, C-MAD arranged a field day on Loyce's farm so her neighbours could see the yield for themselves. They were impressed, and all farmers in the village now intercrop legumes with their maize, sorghum and millet. They have also started planting stylo in cassava fields to control weeds, improve soil fertility and produce fodder.
Local farmers also are intercropping legumes with Napier grass to control striga weeds. A mixture of Napier with stylo, lablab bean, velvetbean or seratro makes good fodder. They do not use sunn hemp as a fodder intercrop as it does not make good forage. —For more information, contact Community Mobilization Against Desertification, Kenya.

Advantages

Some types of green manure provide food or fodder as well as conserving and improving the soil.
Lupin (a fodder legume) is good at recycling phosphorus as well as nitrogen.
Green manures suppress weeds by shading them out. Some legumes reduce the number of striga weeds in the field. Sunn hemp is especially good at this.
Relatively little labour is needed, compared to other ways of adding organic matter.
Green manures are cheap to plant and easy to manage.
Seeds of green-manure crops are easily available.

Disadvantages

The benefits of green manures may be long-term rather than immediate.
It can be difficult to incorporate green manures into an existing cropping system.
Some green-manure crops such as velvetbean and lablab bean may compete with the main crop for light and nutrients. It is important to select green manures carefully so they do not interfere with the main crop.
Some green manures may attract new pests and diseases which attack the crops.
Some green-manure crops may become weeds by seeding and growing in the crop field in the next season.
Green manures may not be successful in the dry season, especially in drier areas.
If a green-manure legume has not been grown in the field before, the soil may not contain the bacteria it needs to fix nitrogen (see the section on Inoculating legume seeds).

Requirements

Green-manure crop seeds.
Inoculant (for some types of legumes).
Hoe.
Sand (for small seeds).

Planting as a pure stand

If you are planting the green manure as a pure stand, follow the steps below:

1. Prepare a seedbed by digging the soil and removing the weeds.

2. Water the seedbed, and plant the seeds or cuttings of the green-manure crop. Space the plants closely so they cover the ground quickly when they start growing.

3. If necessary, weed the plot regularly to reduce weeds and pests.

4. While it grows and flowers, a green-manure legume fixes nitrogen in the nodules onits roots. After flowering, the legume leaves fall off, increasing the amount of organic matter in the soil. With sunn hemp, turn the legume into the soil just after it has flowered.

5. Cut the leaves and stems for fodder if necessary, but do not remove the entire plant or expose the soil surface.

6. Harvest the green-manure crop (eg, the pods).

7. Slash the remaining stalks and leaves and, if possible on the same day, turn them into the soil. You can leave fodder legumes, such as velvetbean and lablab bean, to grow for up to 2 years before slashing them.

8. Leave at least 7 days before planting the next crop to allow the stalks and leaves to decompose.

9. Plant the next crop as a pure stand of cereal, or intercrop again with legumes.

Do's

Choose the right type of green manure for your needs.

Make sure the planting materials do not contain seeds of weeds.

If legume seeds are hard to find, grow a small plot to produce your own.

Use normal spacing for the cereal even if you are intercropping it with a legume.

Mix small legume seeds, such as sunn hemp and stylo, with about the same amount of sand before broadcasting the seeds. This helps give an even stand of the legume in the field.

Use inoculant with soybean seeds to ensure they form large numbers of nodules. Use inoculant with other legumes species if possible (each species of legume needs a different type of inoculant, so make sure you get the right one). See the section on Inoculating legume seeds for details.

Weed the green-manure crop.

Reduce the canopy (for example to prevent an intercropped green manure from interfering with the main crop) by harvesting the crop for fodder.

Don'ts

Don't plant if the soil is so dry or so wet that the crop will not germinate.

Don't allow livestock to graze directly on the green manure. Instead, cut the green-manure crop and carry it to the animals.

Don't harvest large amounts of the legumes as vegetables or fodder.

Planting green manures as an intercrop

You can also plant a green-manure legume as an intercrop between the rows of the main crop. Choose the type of green manure and planting times carefully so it will not grow taller than the main crop and shade it out.

1. Choose a legume species that grows well in your area, and obtain enough seed.
2. For most legume species, plant at the same time as the cereal crop, so the crops can germinate before the heavy rains. Broadcast small-seeded legumes, such as sunn hemp, stylo, red gram and seratro. Plant larger seeds in rows between the rows of cereal. Plant velvetbean and lablab bean about 2 weeks after the cereal, as they grow fast and would shade out the cereal if planted earlier.
3. Continue with steps 3-9 above.

For legumes such as cowpea that form vines, plant one row of the legume between the rows of cereal.

For smaller legumes such as gram, plant two rows of the legume between the rows of the cereal.

Previous

Next