Step 1: Understanding the Concept:
The duration of a crop rotation is calculated based on the total time taken to complete one full cycle of the listed crops across the sequential cropping seasons (Kharif and Rabi).
Step 2: Detailed Explanation:
Let us break down the cropping sequence "Maize - wheat - cotton - berseem":
1. Maize (Kharif) followed by Wheat (Rabi): This constitutes a standard 1-year cropping sequence.
2. Cotton (Kharif) followed by Berseem (Rabi): This constitutes another 1-year cropping sequence.
Together, these four crops are grown sequentially over four distinct seasons (two Kharif and two Rabi seasons).
This entire cycle takes exactly 2 years to complete before returning to the initial crop (Maize).
Therefore, this is a classic example of a two years rotation.
Step 3: Final Answer
The rotation "Maize-wheat-cotton-berseem" is a two years crop rotation.