Concept:Bush fallowing is the main traditional farming system used by rural farmers in Nigeria.
Explanation:Rural farmers in Nigeria predominantly practise bush fallowing, also called shifting cultivation.
In this system, a farmer cultivates a piece of land for a few years until soil fertility declines.
The farmer then abandons that land for a number of years so it can regain fertility naturally through the growth of bush and vegetation.
During the fallow period, the farmer moves on to clear and cultivate another piece of land.
This rotation allows the soil to recover without the use of artificial fertilisers.
It is a common, low-cost method among rural farmers because it requires little technology and follows traditional land-use patterns.
Terrace farming, irrigation farming, and plantation agriculture are not typical subsistence practices of rural farmers in Nigeria.
Therefore, bush fallowing is the correct option.
Answer:D. bush fallowing