Sustainable Agriculture Extension Manual

Contour tree-planting

Farmers plant lines of closely spaced trees across a slope to slow down rainwater flowing down the slope. This reduces the amount of erosion. Over time, soil builds up on the up-slope side of the line of trees, forming a terrace. Farmers plant food crops in the rows between the trees.

A contour is a level line running across the slope. The trees growing along this line bind the soil and build up mounds around their trunks. If the trees are spaced closely, the mounds tend to join together over time, forming a small ridge or dam. When water reaches this ridge, it stops flowing, forms a puddle, and percolates into the soil. This increases the amount of moisture in the soil and raises the water-table.

The trees can also provide fuelwood, mulch or green manure, fodder or fruit.

Location

Contour tree-planting is useful in hilly areas with high rainfall and easily eroded soils.

Advantages

  • The line of trees prevents rainwater from washing soil down the slope. It retains topsoil in the field and maintains soil fertility.
  • The trees provide fodder for animals and fuel for domestic use.
  • Tree leaves can be incorporated into the soil as a conditioner. Leguminous trees can be trimmed and the leaves used as mulch or green manure.
  • The lines of trees encourage the farmer to plough across the slope instead of up-and-down. This further reduces erosion.
  • Fodder grasses or legumes can be grown along the row of trees.

Disadvantages

  • If they are not pruned regularly, the trees may shade the crops growing nearby.
  • The tree roots can be a problem during ploughing.
  • The trees may host pests of the crops.

Requirements

  • Tree seedlings.
  • Hoe; line-level or A-frame.

Procedure

Nursery

1. In a nursery, grow seedlings of the type of tree you want to plant. You can choose various types of tree:

  • Leguminous trees such as leucaena and albizia for fodder, fuelwood and to get green manure from the prunings.
  • Fruit trees for fruit.
  • Other types of trees for building poles and fuelwood.

Laying out the contour

2. Choose a place on the slope where to start.

3. Using an A-frame or line-level, mark a contour line across the slope with sticks or stones. (See the section on Marking contour lines).

4. Dig a hole big enough to plant a tree seedling. Move one pace (about 1 m) along the contour line, and dig another hole. Repeat this until you reach the edge of the field.

5. Move about 10 m (30 feet) up or down the slope, mark another contour line, measure the spacing and dig holes. Do the same thing again until you have marked enough contours on the slope.

 

Do's

  • If a seedling dies, plant a new one in its place.
  • Prune the trees regularly to prevent them from shading the crops in between the tree rows.

Don'ts

  • Don't allow livestock to graze on the seedlings. Instead, prune the trees and carry the forage to the livestock in their sheds.
  • Don't over-harvest the contour-line vegetation, as this may break the continuous ridge line. Water can then begin to flow through the gap and create a gully.

Planting and cropping

6. Plant the seedlings in the holes, and water them if needed. Plant at the beginning of the wet season so the seedlings have time to become established.

7. Plough the soil between the lines of young trees, and plant food crops.

8. Weed the crop and care for the trees. You can leave a strip of grass, grow vegetables, or plant a mixture of fodder grasses and legumes, along the line of trees to help slow down the flow of water.

9. If you are growing leguminous trees, prune them regularly to reduce the amount of shade. Use the prunings as mulch or incorporate them into the soil as organic fertilizer.


Enset

Enset (Ensete ventricosum) is a multi-purpose crop grown in Ethiopia that is useful for contour planting and in sustaining soil fertility. It is sometimes called the "false banana" because it looks like a banana tree. Ethiopian farmers grow enset for various uses: it provides food, feed, fibre, fuel, medicine and construction materials; it also helps conserve soil and water, and provides shelter for coffee bushes. It is widely planted in Ethiopia, where the fleshy stem is processed into a staple food. It is thought that some 15 million people depend directly or indirectly on this crop. Outside Ethiopia, varieties of enset are planted in gardens as ornamentals.

Enset is grown as a pure stand, or can be intercropped with coffee, banana, fruit trees, timber trees or food crops. In the highlands of Gurage, in Hadiya and parts of Kambata zones in southern Ethiopia, where enset is mainly grown as a monocrop, farmers plant it in rows along the contours. It helps control soil erosion on very steep slopes.

Enset has a strong, wide-spreading, deep roots which bind the soil and protect it from erosion. It is a large, perennial plant, so is useful as a windbreak. The leaves are large and break the fall of raindrops. Because it has deep roots, it remains green throughout the dry season, and the roots recycle nutrients from deep in the soil. Farmers prune the leaves of younger plants and leave them on the ground as mulch.

To plant enset, farmers split the corm (the fleshy root) from an enset plant into halves, and plant the pieces in a nursery field in holes spaced 1-1.5 m apart. They apply manure, weed the field and cultivate it carefully to obtain as many suckers as possible. They then separate the suckers and transfer them to the permanent field. They apply manure, cultivate around the enset regularly to control weeds, and prune the younger enset leaves to control the growth of the plant. —For more information, contact Kelsa Kena, Awasa Research Centre, Ethiopia.

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