whole year; entire year; year-round
Refers to the whole span of a year. In modern Japanese this use is often seen in compound-like expressions such as 周年栽培 or 周年営業; 通年 is more everyday for plain 'throughout the year.'
These tomatoes are cultivated year-round in greenhouses.
They are aiming for year-round operation to stabilize local employment.
nth anniversary; year anniversary
Used after a number or event name to count anniversaries: 10周年, 創立50周年, 結婚30周年. It marks the anniversary year or occasion, not simply the number of years elapsed in any context.
A ceremony was held to celebrate the company's 50th anniversary.
Next month, we will celebrate our 10th wedding anniversary.
The company will reach its 100th founding anniversary next year.
Tomatoes are cultivated year-round in this greenhouse.
My parents celebrated their 30th wedding anniversary this year.
The school held a ceremony to commemorate its 50th anniversary.