Customize form Error while creating fields

Hi team ,I created one of the costing module in Erpnext Version 13 as the client needs to determine the cost of every bag. That particular doc type requires allot of different type of fields that i need to create for calculations.
while creating fields using customize form i am getting this error…

pymysql.err.OperationalError: (1118, ‘Row size too large. The maximum row size for the used table type, not counting BLOBs, is 65535. This includes storage overhead, check the manual. You have to change some columns to TEXT or BLOBs’)

Please help me regarding this.