Degradation - Improving Slash And Burn Practices
In “slash and burn” agriculture, cultivated plants benefit from the reduced competition for water and nutrients when the forest is burnt down. But the burning also destroys timber worth billions of dollars in various parts of the tropics.
Below, Professor Nils Nykvist shared his knowledge on how slash-burn agricultural practices can be improved to help reduce land degradation.
By Professor Nils Nykvist
Innovations in slash-and-burn agriculture
Therefore in Burma, a combination of forestry and such slash-and-burn practices, named the taungya system, was introduced in the 1800s. After logging, the slash-burn farmers were allowed to burn and cultivate the land, in return for planting trees. The small tree seedlings were planted so sparsely and grew so slowly at the beginning that they did not significantly reduce the harvest of the agricultural crops.
The advantage for these slash-burn farmers was that they did not have to cut down the trees. For the forest industry, the benefit was that they did not have to clear the tree seedlings from weeds in the first years after planting when the farmers grew their crops.
In the Thai forest villages, the taungya system was improved by adding a social aspect to the cooperation. For each forest village that a state company (the Forest Industry Organization) began building in 1968, a sufficiently large area of forest-land for an entire rotation of the selected tree species was set aside for the farmers .
Each family received approximately 1.6 hectares of a clear-felled area that after burning would be planted with trees and cultivated with the farmers’ own agricultural crops. The crops were grown a couple of years, after which time the soil was less fertile, and the family got a new forest area that after clear-felling and removal of the logs could be burnt and used for tree planting and cultivation.
Benefits of the slash-burn innovations
If the family did a good job with the tree-planting, extra compensation was given in addition to the benefits they already had in the form of free electricity, running water, medical care, schooling, and a plot of land to build houses and grow vegetables.
Thanks to these forest villages, the forest in large areas could be utilized, and the living conditions for the slash and burn farmers improved.
Some slash-burn farmers would not give up their ancient right to self-determination over the land. In Sarawak on Borneo several timber companies have therefore made a deal with the farmers to buy the trees that the farmers cut down for their cultivation .
After the forest company has harvested the timber, the slash and burn farmers burn the ground in the traditional way and plant agricultural crops, in Sarawak, usually mountain rice. Forest companies provide them with small seedlings that the farmers are paid to plant.
When the yield of agricultural crops after a couple of years has fallen too much, due to the loss of plant nutrients, the slash and burn farmers leave the cultivation for a new forest area. The tree seedlings are by then sufficiently grown so that they out-compete weeds and shrubs that would otherwise colonize the land.
When the trees are ready for harvesting, which depends on tree species and soil fertility, the farmers are paid to cut down the trees and plant new tree seedlings before they start a new cultivation of crops.
The tree species planted in Sarawak are usually some species of acacia, which are nitrogen-fixing and thus improve the availability of nitrogen in the soil. The rotation period for planted acacia is about ten years.
Other forms of so-called agroforestry are to plant fast-growing nitrogen-fixing shrubs whose branches regularly are cut off and used as green manure, by which the availability of nitrogen as well as other nutrients in the soil
can significantly be improved (Fig. 23).
Figure 23. Intercropping of teak and mountain rice with the nitrogen-fixing shrub Leucaena leucocephla. In order to avoid having the bush grow out too much and shade the teak seedlings and mountain rice, the branches are cut regularly and placed beside the mountain rice as a form of green manure. Java.
There are many forms of intercropping of agricultural crops and trees all over the world. In Southeast Asia there are small family gardens with trees and ponds where fishes are fed with household waste from the farmer’s own garden. In addition to the farmer’s self-sufficiency in fish, nutrients are recovered that would otherwise be lost through leaching.
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