Windbreaks Protect Crops and Soil

Backgrounder

Here’s some information of special interest to farmers who live in places where the soil is dry. Have you noticed that the soil blows around your fields? Are your crops stunted? Have they stopped growing?

You are not alone. Many farmers worry that they will have to keep moving to find better land for farming. That’s because dry, infertile land is spreading like a disease across many countries. This problem is called desertification. First the land loses its cover of vegetation. Without grasses and trees to help hold it in place, much of the topsoil blows away or is carried away by rain. Only hard, dry, land is left behind.

But the problem can be fixed. Many countries have already taken steps to fight desertification and with your help it can be stopped.

Listen to the following information about a technique that can slow the wind down and protect your crops and soil.

Strong winds can damage your crops and blow lots of soil off your land. Over time, wind can blow so much soil away – all that is left is sand and stone. But a barrier of trees and shrubs can help slow the wind speed and protect your fields and crops. This barrier is called a windbreak.

The most important thing a windbreak does is protect your soil and crops from strong winds. But there are other benefits that you will notice too. Your soil will retain more water. You will have fewer broken branches and torn leaves. And you can harvest the wood from the trees for fuel, or for making poles and furniture.
Making a windbreak
The way you design your windbreak will depend on the wind speed and direction of the winds in your area. Windbreaks work best when they are planted at right angles to the wind direction. For example, if the wind blows from the north to the south, then you should plant the windbreak from the east to the west. Usually, however, winds blow from a number of different directions. If that is the case, you may want to plant dense windbreaks facing the major wind direction and some less dense windbreaks that face the minor directions. Some people build hedges in an L-shape to cover both directions.

Now you’ll have to decide what types of trees are going to make a good windbreak. Choose a few kinds of trees and shrubs that grow naturally in your area. Look around and see which kinds grow well in open or exposed areas. Those trees and shrubs will probably have strong stems or trunks that can resist the force of the wind. They should also have deep roots that grow straight down and don’t spread sideways. If the roots grow sideways too much they will compete with other trees or crops. Some of the trees should have thick foliage.

It is best if the trees and shrubs you choose have other uses too. For example certain species can provide you with fuelwood, leaves for livestock feed, food, and medicines.

Windbreaks can be different widths. Farmers usually plant one to five rows of shrubs and trees. When you are planning the number of rows, remember to consider those valuable products you can harvest from trees.

The taller the windbreak is the more land it will protect. So a windbreak should be as tall as possible, but remember to take into consideration the trees that are well suited to your growing conditions.

The field of crops will be sheltered at distances of 30 times the height of the tallest trees in the windbreak. That is to say, if you measure the height of the tallest trees and then walk a distance that is 30 times that height – away from the windbreak – that is the length of the area that will be protected. Each row of trees in the windbreak should be a different height. If the rows are the same height they will not reduce the wind speed very well.

When it comes to planting you will have to decide how far apart to plant the trees. The distance between the trees will depend on the kind of trees you plant. The main idea is to get a fairly close barrier of foliage. Plan it so that the tree branches will be touching each other after they have been growing for a few years. You may want to plant trees close together at the start and then remove some of them as they grow and the windbreak fills in.

If you have very large fields you will probably need more than one windbreak. It’s best to plant a series of windbreaks across your field, all facing the direction of the wind. As a general rule, space them 200 to 300 metres apart or 20 times the height of the tallest trees. It is the combined effect of many windbreaks over a large area that best protects your crops and soil.

In order to get a good cover of foliage from the ground all the way up to the top of the windbreak you should try to include three types of vegetation.

First, you should have some shrubs that grow about as tall as a man (2 metres). Secondly, you should include small, fast-growing trees or large shrubs that grow to two times the height of a man (4 or 5 metres). Lastly, it is a good idea to plant some tall trees. Plan to put the tallest trees in the middle row or rows and shorter trees and shrubs on the outside edges. A good windbreak slows the wind but doesn’t block its passage. In other words a hedge must allow some wind to pass through it. But try to make sure that there are no large gaps or openings in the windbreak. When wind rushes through gaps, the force of the wind can actually get stronger. If this happens a large section of the windbreak will no longer protect your crops and soil.

Building a windbreak can bring you many benefits over time: food, fuel, and most, importantly, protection for your land from strong winds.
Notes
Tree species recommended for windbreaks

From the “Agroforestry Technology Information Kit” published by the International Institute of Rural Reconstruction, Silang, Cavite, Philippines.

Tall Trees (Over 15 metres)

• Casuarina equisetifolia
• Pterocarpus indicus
• Tectona grandis
• Gmelina arborea
• Vitex parviflora
• Artocarpus blancoi
• Chrysophyllum cainito
• Sandoricum ketjape
• Tamarindus indica

Medium Sized Trees (5-15 metres)

• Pithecellobium dulce
• Anacardium occidentale
• Diospyros philippinenses
• Lagerstroemia speciosa
• Leucaena leucocephala
• Gliricidia sepium
• Albizzia procera
• Casuarina rumphiana
• Syzygium cusini

Shrubs & Bamboo (up to 5 metres)

• Bambusa blumeana
• Bambusa vulgaris
• Bambusa spinosa
• Bougainvillea spectabilis
• Acacia farnesiana
• Schizostachyum lumampao
• Erythrina variegata
• Cajanus cajan

What is the United Nations Convention to Combat Desertification?
It is an agreement signed by countries around the world to share the responsibility of fighting the effects of desertification. Its goal is to help regenerate the soil in arid, semi-arid, and dry sub-humid regions. The Convention came about at the Earth Summit in Rio de Janeiro, Brazil, in 1992, where many developing countries, led by African countries, asked for the world’s help in fighting desertification as quickly as possible.

In Paris, 1994, 87 countries signed the United Nations Convention to Combat Desertification. Today more than 115 countries have signed the agreement. Once the governments of 50 countries have fully confirmed their participation the full course of action will begin. A plan for urgent action has been adopted to encourage immediate efforts in Africa because it is the part of the world which suffers the most from desertification.
What causes desertification?
Desertification is caused by changes in climate and by human activities. Drought sometimes makes soil dry up and crack, or makes the soil problems that already exist even worse. But there are four main ways that people make deserts: by overcultivating the soil, by allowing animals to overgraze the land which removes the covering of vegetation that protects it from erosion, by cutting down or burning trees, and by using improper watering methods which turn cropland salty.
What kind of action will be taken under the Convention?
One of the key elements of the Convention is what is called a “bottom-up approach”. This means that people in small communities and their leaders will be consulted before decisions or actions are taken. The people in these communities will be involved in projects to stop desertification in their area. The Convention recognizes that people in affected communities, non-governmental organizations, experts, and governments must work together to fight desertification effectively and to find long-term solutions. That means farmers and scientists should share ideas about what the most appropriate farming techniques are. These ideas can be discussed with government and non-government organizations so that funds can be properly allocated.