Assertion: Slash and Burn agriculture is also called Shifting cultivation.
Reasoning: The vegetation is usually cleared by fire, and the ashes add to the fertility of the soil. This land is cultivated for some time (3 to 5 years) after which this parcel of land is abandoned and new patch of land is cleared for cultivation.

Both Assertion (A) and reasoning (R) are correct and R is the correct explanation of A.

Primitive subsistence agriculture or shifting cultivation is widely practised by many tribes in the tropics, especially in Africa, south and central America and south east Asia. The vegetation is usually cleared by fire, and the ashes add to the fertility of the soil. Shifting cultivation is thus, also called slash and burn agriculture. The cultivated patches are very small and cultivation is done with very primitive tools such as sticks and hoes. After sometime (3 to 5 years) the soil looses its fertility and the farmer shifts to another parts and clears other patch of the forest for cultivation. The farmer may return to the earlier patch after sometime.