Similar names: Covering, Groundcover, Topping, Blanket mulching
Mulching involves applying a layer of material to the soil surface mainly in order to improve soil health and enhance plant growth. Either organic or inorganic materials can be used as mulch. Mulching simulates a natural forest environment. In a natural forest, soil is covered by leaves and organic material, and it is rich in living organisms that recycle nutrients. Mulch can be composed of a wide variety of materials (see method of application) and has a number of potential uses. It is an especially helpful technique in climactic zones with high evaporation rates.
The physical and ecological benefits of mulching are numerous. Firstly, the layer of mulch helps retain soil moisture by reducing the soil’s exposure to direct sunlight and preventing evaporation. Mulching is also effective at stifling weed growth by physically impeding their growth and stopping their access to sunlight needed for photosynthesis (amongst other mechanisms of weed prevention such as allelopathy with certain mulching materials). Other benefits of mulching include that it helps prevent soil erosion, is an effective means of regulating soil temperature by acting as insulation and improves the fertility and structure of soil (especially organic mulching). Please refer to the conditions section for information on potential problems with mulching so as to ensure the best chances of successful implementation.
Practitioners should take precautions to ensure the optimal implementation of mulching to avoid any undesired effects:
- When using organic mulching material, it is important to make sure these do not contain seedlings so as to prevent undesired sprouts from growing.
- If the layer of mulch applied is too thin, it may be easily washed away by rain, leading to a need for reapplication. Furthermore, a thin layer of mulch doesn’t prevent sunlight from reaching weeds and may promote weed growth as these take advantage of the beneficial growing conditions.
- Applying an excessive layer of mulch may prevent rainfall from infiltrating the ground. Furthermore, too much mulch on top of poorly drained soil may cause waterlogging and be damaging for plant growth.
- Consider that If crop residues are used for mulching, this residue can no longer be used for animal feed.
- Untimely mulching, or using the wrong mulch for a particular crop, can slow its growth and leave it more vulnerable to weed competition. Please refer to the Mulching Limitations and Pitfalls section of this link for more specific information.
Machete or similar a tool to cut residue (e.g. leaves, branches)
Shovels and wheelbarrows in order to pick up and carry mulch material
Rake to smooth over finer-textured mulch
*Material required may change depending on the mulching material being used
Steps of implementation
- Select/identify the mulching material:
Select the mulch based on your what you want to achieve by using mulching. Consider which effects you want to realize for plant and soil health as well as the accessibility and cost-effectiveness of the materials you will use. In many agricultural and agri-forestry systems, the residues from existing crops and surrounding vegetation can be a very cost-effective mulching material. This can include the leaves and branches of nearby trees, or the remaining plant residues left over from crop harvesting.
Common mulching materials:
- Grass clippings – easily accessible and rich in nitrogen
- Shredded leaves – rich in nutrients and improve soil fertility.
- Wood chips – A good all-around material but relatively expensive
- Straw or hay – efficient in saving moisture and in keeping weeds away.
- Compost – improves soil structure.
- General crop residue – Uses available material and is cheap.
- Cover crops as mulch – Enables for additional economic revenue.
- Inorganic mulches (i.e., gravel or stone) – efficient in allowing air to circulate and water to infiltrate.
- Determine mulching needs and constraints:
The amount of mulch applied as well as the positioning of this mulch for optimal results will vary depending on the context and purpose of application. Determine whether any plants will be harmed by the mulch of choice. Also check that soil drainage throughout the mulching area is adequate. Mulching usually retains moisture, making it potentially hazardous for plants if a thick layer of mulch is applied in an area where water is already slow to drain.
If mulch is already present, check the depth and state of the mulch. Do not add additional mulch if a sufficient and healthy layer is already present, instead rake and spread out the existing layer
- Spread the mulch:
Without covering the base of crops and trees (so as to avoid diseases caused by excess moisture) apply an even layer of mulch on the selected area. Mulch may be spread over a seed bed, within planting holes, or over an entire farm. Generally, it is recommended that a generous 5-10 cm layer of mulch be applied in well-drained soils. Especially if mulching with the aim of weed prevention, a thick-enough layer to stop sunlight reaching weeds should be applied.
Mulch should be replaced or supplemented whenever it shows signs that it is deteriorating and becoming less useful. Such signs could be for example: breakdown of material, soil erosion, discoloration, etc. There is no set time period for replacing mulch. Most commonly this is done on a yearly basis but may be needed as little as 6 months after initial application or up to 2 or 3 years depending on the material and context.
The cost of mulching will vary a lot depending on the type and availability of mulch material, labor costs and application method. The labor intensity of mulching as well as local labor costs in China and Ghana vary significantly compared to the Kenyan context. This explains the widely divergent costs of the intervention in these contexts.
|Mulching material||Maize crop residue||Maize crop residue||Banana leaves|
|Case study||Maize straw-maize. Nwabiagya-Ashanti, Ghana||Maize straw-maizeChangchun, China||perennial cropping: banana/plantain & coffeeEmbu, Kenya|
|Establishment costs||120 USD||122 USD||0.7 USD|
|Labor time||56 hours/ha||56 hours/ha||2 hours/ha|
|Maintenance costs||none mentioned||none mentioned||0.19 USD/6 months|
|Benefits||179 USD/ha||249 USD/ha||Not measured|