We should follow a luni-solar calendar?

[w3bcrowf3r]

How can we follow a luni calendar? This contradicts: http://corpus.quran.com/wordbyword.jsp?chapter=12&verse=47#(12:47:1)

If it's luni only, the verse has an error. Or is it the current luni only calendar that is in error?
Because in 7 years, according to a luni calendar, u can't harvest anymore due to the seasons. Harvesting "7 years" according to a luni only calendar will take more then 7 years since you will need to wait for the seasons, because the current calendar moves every year 1 month.

There are a lot of other verses which are very clear about using the sun and the moon. Such as 10:5, which says it literally.