Heter Mechira
In the late 19th century, in the early days of Zionism, Rabbi Yitzchak Elchanan Spektor came up with a halakhic means of allowing agriculture to continue during the Shmita year. After ruling in favor of Minhag Yerushalayim, that the biblical prohibition consists of not cultivating the land owned by Jews ("your land", Exodus 23:10), Rabbi Spektor devised a mechanism by which the land could be sold to a non-Jew for the duration of that year under a trust agreement. Under this plan, the land would belong to the non-Jew temporarily, and revert back to Jewish ownership when the year was over. When the land was sold under such an arrangement, Jews could continue to farm it. Rabbi Abraham Isaac Kook, the first Chief Rabbi of British Mandate Palestine, adopted this principle, which became known as the heter mechira (lit. "sale permit").
The heter mechira was accepted by Modern Orthodox Judaism and is one of the classic examples of the Modern Orthodox approach toward adapting classical Jewish law to the modern world. However, this approach has not been universally accepted in the Orthodox community and has met with opposition, particularly from Haredi poskim (authorities of Jewish law).
In contemporary religious circles these rabbinic leniencies have received wide but not universal acceptance. In Israel, the Chief Rabbinate obtains permission from all farmers who wish to have their land sold. The land is then legally sold to a non-Jew for a large sum of money. The payment is made by a cheque post-dated to after the end of the Sabbatical year. When the cheque is returned or not honoured at the end of the year the land reverts to its original owners. Thus, the fields can be farmed with certain restrictions.
Although the Orthodox Union's Kashrut Division accepts Minhag Yerushalayim and hence regards the produce of land owned by non-Jews as ordinary produce, it does not currently rely on the heter mechira because of doubts about whether the trust arrangement involved effects a valid transfer of ownership.
Some Haredi farmers do not avail themselves of this leniency and seek other pursuits during the Shmita year.
Read more about this topic: Shmita