History of Pohela Boishakh..................
Akbar the Mughal emperor was collecting the tax under his reign from 1556 to 1609. On the times, the economy was fully depended on the Agricultural productions. That was the time; the Arabic or Hijri year didn't match for collecting the Agricultural products as the Tax.
Then he made a new calendar to collect the Tax from the people who were fully depended on the Agricultural products. That Calendar was named as Bangla calendar and the 1st day of this calendar known as the Pohela Boishakh.
SOURCE Pohela Boishakh 2017: History And Celebration