Soil Cover and Reforestation

Compiled by:
Beat Stauffer (seecon international gmbh), Nina Carle (seecon international gmbh) , Dorothee Spuhler (seecon international gmbh)
Adapted from:
FAO (Editor) (2005)

Executive Summary

Soil cover and reforestation is a mechanism to protect soil from water loss. Like the protection of an umbrella, soil cover and reforestation protects the soil and the microbes within from the impact of sun heat, rain and wind. It stops the soil surface from sealing, and reduces the amount of precious rainwater that runs off.

Introduction

With a reduction of moisture loss in the soil, groundwater resources are protected, soil quality and agricultural production can be improved, and water use for irrigation can be decreased, thus optimising the local water cycle. Soil moisture loss (and also soil degradation) can be minimised through different techniques of soil moisture conservation: soil cover (with living plants) and reforestation, mulching, different tillage techniques, and soil amendments. Soil cover is common on agricultural land. Reforestation is common to protect water protection areas and groundwater resources, or to prevent soil degradation in non-agricultural sites.

Benefits of Soil Cover

As a result of soil cover, agricultural production subsequently improves because soil cover both promotes and maintains optimum soil conditions for plant growth (nutrient availability) and water infiltration (water availability). Soil cover with living plants (soil can also be covered with mulch) protects the soil surface from rain, wind and sun (FAO 2005):

  • It reduces soil erosion and protects the fertile topsoil, thus preventing the silting of rivers and lakes.
  • It stops the soil surface from sealing, and reduces the amount of precious rainwater that runs off.
  • It suppresses weeds by smothering their growth and reducing the number of weed seeds. This reduces the amount of work needed for weeding.
  • It increases the soil fertility and the organic matter content of the soil.
  • It increases soil moisture by allowing more water to sink into the ground and by reducing evaporation.
  • Decomposing vegetation and the roots of cover crops improve the soil structure and make the clumps and lumps in the soil more stable – making it harder for rain to break them up and wash them away.
  • Earthworms and other forms of life can prosper in the cover as well as in the soil.
  • Soil cover stimulates the development of roots, which in turn improve the soil structure, allow more water to soak into the soil, and reduce the amount that runs off.

Water Management

  OMAFRA (2011)

Even a small amount of crop residue can provide a benefit to a growing crop under extremely dry conditions. The residue moderates soil temperatures and help to reduce evaporation of soil water. Source: OMAFRA (2011) 

As mentioned above, soil cover can reduce soil moisture loss. In contrast, some growers use cover crops such as rye as a way to reduce soil moisture in early spring. The crop takes up the soil moisture and uses it within the plant. The water is incorporated in the plant tissues or is transpired. In both cases, the water is removed from the soil. This use of cover crops requires very good management and understanding of plant growth habits. Under warm wet conditions some cover crops can become very difficult to control either with tillage or chemically. Also, under dry spring conditions the cover crop should be controlled earlier to prevent excessive moisture loss, which may interfere with crop establishment and growth (adapted from OMAFRA 2011).

Types of Soil Cover and How to Choose the Right One

There are two main types of soil cover:

  • Living plant material: crops, cover crops and forest structures.
  • Dead plant material such as crop residues and prunings from trees and shrubs (see also mulching).

  in between the collards in this field is a cover crop mix of rye, hairy vetch and crimson clover, which provides a lush cover protecting the soil from harsh winds and eroding/compacting rains. Source: TILLER (2012)

A field of cover crops: in between the collards in this field is a cover crop mix of rye, hairy vetch and crimson clover, which provides a lush cover protecting the soil from harsh winds and eroding/compacting rains. Source: TILLER (2012) 

In conservation agriculture, a combination of mulch and living plants to keep the soil covered is common. To obtain a good soil cover, crop residues (e.g. maize stalks) can be left in the field or additional dead plant material from outside the field (e.g. cut grass or leaves) can be added (see also mulching and soil amendment).

In addition, cover crops can be planted, either during the cropping season (to cover the area in between the crop rows), or afterwards to cover the whole field. During the cropping season, the crops themselves act as soil cover. An intercrop of tall plants (such as maize) and low-growing plants (such as beans) make a good cover. It can be difficult to keep the soil covered, especially in semi-arid areas. It may be necessary to compromise: some cover is better than none (FAO 2005).

How to Choose a Cover Crop

Growing cover crops is a common soil management practice. There are a lot of good reasons to grow cover crops but it is often hard to put a dollar value on the return from growing them. Cover crops are an important part of a system of soil maintenance - particularly important on the lighter soils with lower organic-matter or on fields with short rotations and little return of crop residue or manure. It is important to know the goal when planting a cover crop and to select the best one for that job. Small-scale farmers prefer a cover crop which fits into their normal cropping system and which has multiple purposes (FAO 2005):

  • Edible seeds and vegetables
  • Soil fertility
  • Animal fodder
  • Firewood/fencing material
  • Weed suppression
  • Medicines.

First, check which cover crops grow well in your area. This depends on the soil type, rainfall, temperature and altitude. If you live in an area with little rainfall, select a cover crop that grows quickly, such as cowpea, desmodium, lablab, lucerne, mucuna, or pigeonpea. Then check how much work each cover crop will need: for land preparation before planting, weeding, and producing and harvesting the seeds. Species with big pods and grains (such as pigeonpea and mucuna) are easier to deal with than species with small pods (such as vetch and grasses). Most farmers prefer species that cover the soil quickly and completely, and which can also be used for food and fodder. As a support to decide which cover crop is suitable and when it should be planted, FAO (2005) recommends answering the following questions:

Questions to help deciding when to plant the cover crop:

  • How much moisture will the cover crop need to grow and produce enough mulch and seed?
  • At what time of year will there be enough moisture for the cover crop to grow?
  • What other factors (temperature, frost) will favour or hinder its growth? Is it sensitive to the day length? To frost? To drought?
  • How easy will it be to manage the cover crop while it is growing and afterwards (mulch management)?

Questions about the cropping system:

  • When will cover be most needed?
  • How fast will the cover crop grow and provide the required cover?
  • How long will the cover last?
  • Might anything (grazing by animals, burning, etc.) reduce the amount of cover?
  • How to stop the cover crop and main crop from interfering with each other?

As already mentioned, it is important to know the goal when planting a cover crop and to select the best one for that job. The following table looks at the various reasons for including cover crops in a rotation (see also crop rotation) and the potential cover crops that best meet those goals. These may vary for other climates and countries.

Cover Crop Function

Best Choices for Cover Crops

Nitrogen production

Legumes - red clover, peas, vetch

Nitrogen scavenging

Fall uptake - oilseed radish and other brassicas, oat

Winter/spring uptake - rye, winter wheat

Weed suppression

Fast growing/shading plants - oilseed radish and other brassicas, winter rye, buckwheat

Soil structure building

Grasses - oat, barley, rye, wheat, triticale, ryegrass or fibrous root systems such as red clover

Compaction reduction

Strong tap roots that grow over time - alfalfa, sweet clover

Biomass return to soil

Fall seeded - oat, oilseed, radish
Summer-seeded - millets, sorghum, sudangrass, sorghum sudan

Erosion protection, i.e., wind, water

Winter rye, winter wheat, ryegrass (well-established), spring cereals seeded early

Emergency forage

Fall - oat, barley, wheat, rye, forage brassicas

Summer - millets, sorghum, sudangrass, sorghum sudan

Nematode suppression

Cutlass mustard, sudans/sorghums, pearl millet, marigold (Crackerjack, Creole), oilseed radish (Adagio, Colonel)

Note: Not all cover crops have the ability to suppress nematode populations; some will even act as hosts. Cover crop activity is variety- and nematode-specific. To get the most activity, cover crops should be weed free and may require specific handling.

Matching cover crop choices to function. These suggestions are matched to the climate of Ontario, Canada. It may change in other countries or climates. Source: OMAFRA (2011)

Reforestation

Generally it is accepted that tree removal by logging, forest fire or wind damages increases runoff (ZOMER et al. 2006). Deforestation, especially in tropical nations, leads to extensive areas of degraded land. In many of these places, even firewood has become so scarce that certain foods requiring cooking have been eliminated from the diet. People must use crop residues and dried dung for fuel, which robs the soil of organic matter and nutrients and accelerates erosion. Soil eroded from degraded lands fills riverbeds, reservoirs and lakes, increasing the severity of floods and causing water scarcities (OTA 1983).

First of all, inappropriate land-use practices on forest lands should be prevented. If not possible, reforestation is one way to improve the productivity and protection of many degraded lands, and provide useful products for the people. Trees have positive effects on human beings (e.g. food, fuel, fodder) and protect soil from heat, rain and wind. Soil temperatures are lower under tree canopies, permitting reaccumulation of organic matter that restores soil structure and microbiota and enhances moisture- and nutrient-holding abilities. Bacteria on the roots of some trees fertilise soil with nitrogen, while fungi on tree roots can convert soil minerals to useful forms. In dry areas, trees can help to prevent the rise of saline groundwater. Where surface soils are dry or infertile, deep tree roots can tap underground reservoirs of nutrients and water and bring them to the surface (OTA 1983). Furthermore, planted trees absorb carbon, which is an important factor when we discuss about climate change. Ten key points on plantation impacts on stream flow can be read in KEENAN et al. 2006.

Example: The Neem Tree

  INFONET BIOVISION (2011)

Neem trees before planted into the soil. Source: INFONET BIOVISION (2011) 

The neem tree is native to India and Southeast Asia, but it is now grown in the warm lowland tropics as well as in arid and semi-arid areas of the world. Neem seems to be a good candidate for planting in most warm parts of the world. It grows vigorously in many semiarid and tropical areas and is regarded as a valuable forestry species in many parts of Africa; but even there it could become more widely employed. It is a multipurpose species that provides villagers with various products from which to derive an income during the years when the trees are maturing. It is also promising for planting in areas suffering desperate fuel wood shortages. It is useful as a windbreak, exceptional as a city tree, and it can grow in (and may even neutralise) acid soils in the tropics. On the farm and around the house, neem is useful not only as a windbreak and a welcome source of shade, but its seedcake is a good fertiliser, as it contains nitrogen, potash, phosphorus, calcium and magnesium (INFONET BIOVISION 2011).

Costs Considerations

There are additional costs above and beyond normal cropping practices that must be considered in systems that include cover crops. Extra expenditures include the cost of the cover crop seed as well as labour and time for planting. Also, special or alternative equipment may be needed to handle the greater amounts of residue present in no-till systems. Cover crops must be managed like any other crop produced in the farm operation (adapted from PENNSTATE 1996).

Reforestation also costs money, e.g. for labour (growing, planting) and seedlings. On the other hand, there are many advantages and money can be saved (fire wood, food, enhanced soil conditions).

Operation and Maintenance

Soil cover management needs expert knowledge. The following list outlines some challenges you may encounter for maintaining soil cover and some ways to overcome them (adapted from FAO 2005):

  • Semi arid areas: In semi-arid areas, where there is little rain and most of it falls in one season, establishing a cover crop may be difficult. Crops, shrubs and trees produce few residues, and farmers often need them for feed or building materials. Cover crops use precious water.
  • Diseases and pests: Diseases and insect pests might attack the cover crop and will require special attention. Farmers often use fire to destroy pests and diseases. But this leaves the soil bare and destroys valuable organic matter.
  • Rats: A dense cover crop may encourage rats, which may attack the crop. Slash cover crop as close to the ground as possible, use traps (poison could kill other animals as well), or use rotating crops (interrupt food supply).
  • Termites: Many farmers fear that soil cover will attract termites. Only a few types attack crops, most of them are important (break down of soil organic matter, aeration).
  • Fire: Bushfires or uncontrolled fires on neighbouring fields can spread into a conservation agriculture field and destroy its soil cover. To prevent this, you can leave a buffer zone around your field.
  • Livestock: Livestock need to be fed. Farmers often allow them to graze on stubble or on fallow fields, and other livestock owners may not keep their animals out of a field planted to a cover crop. This may especially be a problem in dry years or in semi-arid areas, where few alternative sources of feed are available. Fence crop field or find alternatives.

Trees also need to be maintained, especially at the beginning. During growth and irrigation, additional nutrients may need to be provided. Trees must be protected from the above-mentioned impacts as well.

At a Glance

Working Principle

Covering crops and shady trees protect the soil from erosion, evaporation, weeds, and increases biological activity, improves the organic matter and nutrient content, and positively influences root growth and soil structure allowing for enhanced infiltration.

Capacity/Adequacy

Agricultural production improves because soil cover both promotes and maintains soil in optimum condition for plant growth (nutrients) and water infiltration (water availability). Groundwater reserves are protected as evaporation and soil erosion are reduced.

Performance

Huge potential to prevent water loss from soil.

Costs

When using self grown seeds the costs are rather low. It may be necessary to make use of pesticides, and then the costs will rise.

Self-help Compatibility

Can be done by any farmer. If soil cover replaces tillage, it might not lead to additional work required.

O&M

A regular replacement of the decomposed material is necessary.

Reliability

Reliable method, due to its simplicity and self-help compatibility.

Main strength

Simple low-tech method to prevent water loss in agriculture and protect soils, surface water sources and groundwater reservoirs.

Main weakness

May require the investment in pesticides.

Applicability

Soil cover is applicable for every farm. It needs only little expertise and after understanding the basic principles it is a very sustainable tool in agriculture.

Advantages

  • Increases soil fertility and soil moisture
  • Protects soil from sun, wind and rain, reducing evaporation and compaction
  • Plant debris provides organic matter and nutrients to the soil
  • Reduces erosion
  • Prevents silting of rivers, lakes and reservoirs
  • Reduces runoff and enhances infiltration
  • Reduces work for weeding

Disadvantages

  • Pesticides may need to be used
  • To prevent from bushfires, a buffer zone around the field is necessary

References Library

FAO (Editor) (2005): Conservation Agriculture - Chapter 5: Soil Cover. Rome: Food and Agricultural Organization of the United Nations (FAO). URL [Accessed: 03.10.2012].

INFONET BIOVISION (Editor) (2012): Neem: General Information and Agronomic Aspects. Zurich: Biovision. URL [Accessed: 03.10.2012].

KEENAN R.J.; GERRAND, A.; NAMBIAR, S.; PARSONS, M. (2006): Plantations and Water: Plantation Impact on Stream Flow. Canberra: Australian Government Bureau of Rural Sciences Headquarters. URL [Accessed: 01.03.2012].

OMAFRA (Editor) (2011): Cover Crops: Adaptation and Use of Cover Crops. Guelph: Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA). URL [Accessed: 16.02.2012].

OMAFRA (Editor) (2011): Soil Management: Building a Healthy Soil. Guelph: Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA). URL [Accessed: 26.04.2012].

OTA (Editor) (1983): Sustaining Tropical Forest Resources. Office of Technology Assessment (OTA). URL [Accessed: 27.04.2012].

PENNSTATE (Editor) (1996): Cover Crops for Conservation Tillage Systems. University Park: The Pennsylvania State University. URL [Accessed: 27.04.2012].

TILLER, A. (2012): Farmers Try Cover Crops to Protect Their Product. New York: The Bluegrass Special. URL [Accessed: 25.04.2012].

ZOMER, R.J.; TRABUCCO, A.; STRAATEN, O. van; BOSSIO, D.A. (2006): Carbon, Land and Water: A Global Analysis of the Hydrologic Dimensions of Climate Change Mitigation through Afforestation/Reforestation. Colombo: International Water Management Institution (IWMI). URL [Accessed: 27.04.2012].

Further Readings Library

Reference icon

FAO (Editor) (2005): Conservation Agriculture - Chapter 5: Soil Cover. Rome: Food and Agricultural Organization of the United Nations (FAO). URL [Accessed: 03.10.2012].

Conservation agriculture is presented in this handbook of the World Food and Agriculture Organisation FAO and aims to produce high crop yields while reducing production costs, maintaining the soil fertility and conserving water. It is a way to achieve sustainable agriculture and improve livelihoods. Chapter 5 concentrates on soil cover.


Reference icon

FAO (Editor) (2008): Forests and Water. Rome: Food and Agricultural Organization of the United Nations (FAO). URL [Accessed: 27.04.2012].

This thematic study on forests and water was developed in the context of the Global Forest Resources Assessment programme. It is directed to a broad range of technical experts, scientists and decision-makers, particularly national authorities, and presents recommendations on giving more attention to the role of forests and trees in water protection and management at the national level. It also calls for stronger collaboration between the water and forest communities.


Reference icon

HEANEY, A.; BEARE, S.; BELL, R. (2000): Targeting Reforestation for Salinity Management. In: Australian Commodities 7, 511-518. URL [Accessed: 27.04.2012].

Targeted reforestation is likely to be a more cost-effective strategy to manage salinity rather than broad scale land use change.


Reference icon

KEENAN R.J.; GERRAND, A.; NAMBIAR, S.; PARSONS, M. (2006): Plantations and Water: Plantation Impact on Stream Flow. Canberra: Australian Government Bureau of Rural Sciences Headquarters. URL [Accessed: 01.03.2012].

This paper presents results of recent analyses of plantation areas and other types of land cover in major plantation regions and a brief review of scientific literature relating to water use by forest plantations.


Reference icon

MUTCH, D.R.; MARTIN, T.E. (n.y.): Cover Crops. Washington, D.C.: Sustainable Agriculture Publications – USDA. URL [Accessed: 27.04.2012].

A well-illustrated paper about cover crops which answers all important questions.


Reference icon

OTA (Editor) (1983): Sustaining Tropical Forest Resources. Office of Technology Assessment (OTA). URL [Accessed: 27.04.2012].

Where human pressure on natural resources increases rapidly, natural vegetation recedes and soil fertility drops. This triggers a chain of events: adverse changes in microclimates, reduced biologic soil activity, increased wind and water erosion, and pressures to open additional land to compensate for reduced fertility, etc., all leading to yet more pressure and more rapid deterioration of the soil and vegetative cover. Read more about it here.


Reference icon

PENNSTATE (Editor) (1996): Cover Crops for Conservation Tillage Systems. University Park: The Pennsylvania State University. URL [Accessed: 27.04.2012].

An understanding of the cropping system is necessary before selecting a cover crop. Characteristics important for cover crop selection include life cycle, seeding date and rate, winter hardiness, nitrogen fixation or scavenging ability, feed or forage value, and establishment costs. No single cover crop or system will provide all these benefits. Therefore, experimentation may be necessary before producers decide on a suitable cover crop for an individual system.


Reference icon

ZOMER, R.J.; TRABUCCO, A.; STRAATEN, O. van; BOSSIO, D.A. (2006): Carbon, Land and Water: A Global Analysis of the Hydrologic Dimensions of Climate Change Mitigation through Afforestation/Reforestation. Colombo: International Water Management Institution (IWMI). URL [Accessed: 27.04.2012].

This report highlights the potentially significant impacts on the hydrologic cycle and the importance of considering secondary effects, particularly with regard to water, resulting from the widespread adoption of global climate change mitigation measures.


Case Studies Library

Reference icon

BRATEN, R.H. (n.y.): Collective Action Reforestation. A Case Study from Malawi. Oslo: University of Oslo. URL [Accessed: 27.04.2012].

This paper analyses why a certain reforestation project was successful in some villages in Malawi, while not in others.


Reference icon

UW EXTENSION (Editor) (2012): Cover Crops Case Studies: Gary Sommers Farm. Madison: University of Wisconsin Extension. URL [Accessed: 03.10.2012].

This case study shares the experience of one Wisconsin farmer who has been growing cover crops on his cash grain farm for twenty years. He presents his philosophy of cover crop use, explains what cover crop management practices have and have not worked on his farm, and describes what benefits he sees from growing cover crops. Farmers and researchers can use this information as a starting point to explore how they might develop cover crop systems to meet their own goals.


Training Material Library

Reference icon

HDRA (Editor) (1998): The Neem Tree. Coventry: HDRA - The Organic Organisation. URL [Accessed: 27.04.2012].

This paper gives you an overview about the neem tree and its benefits.


Reference icon

ITTO (Editor) (2006): Guidebook: For the Formulation of Afforestation and Reforestation Projects under the Clean Development Mechanism. Yokohama: International Tropical Timber Organization (ITTO). URL [Accessed: 03.10.2012].

The purpose of this guidebook is to serve as guidance for those interested in developing a land-use change and forestry project under the Clean Development Mechanism (CDM) of the Kyoto Protocol. The guidebook has been created by Winrock International, in collaboration with the International Tropical Timber Organization.


Important Weblinks

http://www.ontario.ca/crops [Accessed: 13.02.2012]

The Ontario Cover Crop Council provides information about different cover crop species.

http://www.mccc.msu.edu/ [Accessed: 03.10.2012]

The Midwest Cover Crop Council provides information about different cover crop species.

http://www.fao.org/ [Accessed: 13.02.2012]

FAO website for the correct use of chosen methods in conservation agriculture with a focus on Africa

http://www.omafra.gov.on.ca/ [Accessed: 06.10.2010]

This online factsheet by the Ridgetown College of Agricultural Technology in Ontario, Canada, explains the various causes and effects of soil erosion either by wind or water.