Step 1: Understanding the Concept:
Tillage operations are divided chronologically into primary tillage (initial heavy soil breaking) and secondary tillage (seedbed refinement).
Step 2: Detailed Explanation:
The Mouldboard (M.B.) Plough is a heavy primary tillage implement designed to cut a rectangular furrow slice, invert the soil layer, bury crop residues and weeds, and shatter compacted subsoil layers.
Secondary tillage implements include disc harrows, cultivators, and plankers.
Step 3: Final Answer:
Hence, M.B. Plough is used as a primary tillage implement.