PERIOD
1st Bais HaMikdashnd Bais HaMikdashAfter Churbanth year of cycleShmitah Yovel
st year of cycle
th year of cycle
Shmitahth year of cycle
Shmitah Yovel Counted but not observed
st year of cycle
th year of cycle
Shmitahth year of cycle
Shmitah
st year of cycle
nd year of cycle
Shmitah
st year of cycle
During the time of Ezra the court would count the years towards Yovel, but only in order to keep Shemita at the proper times. However, the actual sanctity of the Shemita year was not dependent on the count. Only the knowledge of when Shemita actually was utilized this counting, but the holiness of the year happened by itself when the time came. As such, it would seem that there can be Shemita even when there is no Yovel.
There is a deeper explanation for this based on the different sanctities that time can have. There is a type of holiness of time that is automatic, such as Shabbat, and a type of sanctity that comes from the Jewish people, such as that of the holidays which only comes when the Jews say it does (since the Jews set the calendar). Shemita confers a holiness that is independent, not reliant on the Jewish count, while Yovel comes about only as a result of the fifty-year counting process undertaken by the Bais Din. Thus, the counting of Shemita by Bais Din is not for the Shemita, but is only for the purposes of the next Yovel. And thus, when Yovel is no longer kept there is no longer a need for counting Shemita years.
However, once the Bais HaMikdash is rebuilt and the counting of the years for Yovel is restored, then the counting of the Shemita years will be restored as well, as a function of Yovel and as a function of the overall sanctity of the land of Israel.
