Primitive subsistence agriculture is practiced widely by many tribes in tropics, especially in Africa, South and Central America and South – East Asia. Under this type of agriculture, the cultivated patches are very small and the tools used are primitive as sticks and hoes. After some years, the soil loses its fertility and the farmers shift to another part and clear some other patch of forest for cultivation. The farmers may return to the earlier patch after sometime. One of the major problems of this type of cultivation is that the cycle of fertility becomes less and less in different patches.