The farm now has 30,000 hetares of land ,more than two-third

The farm now has 30,000 hetares of land ,more than two-thirds of which are under cultivation.
后面这半句不懂 这个which是什么东西 从句是从哪里开始的?或者说 是不是省略了什么呢?总感觉缺少成分的