According to the Torah, the people of Israel were to give the land a rest by letting it go fallow every seven years. Such a year of rest was called a Sabbatical year or Shenat Sh'mittah - year of release.  Evidently the land was go wild during that time, and there was to be no human intervention such as weed control or fertilization. "Do not prune your vineyards" says Leviticus 25:3.  It must have taken some faith to leave it alone! According to Leviticus. 25:21 the people were to trust God to provide a harvest in the sixth year sufficient to hold them through the seventh (while they let the land rest) and the eighth (while they wait for a new crop to grow). This was to remind the people that the land is really God's. (Lev. 25:23)

Every seven sabbatical years there was to be a year of Jubilee, proclaimed with a blast of the Ram's horn at Yom Kippur. (Lev. 25:8-9) At that time any land which had been sold to pay off debt was to be returned to the original owner, and Israelites who had sold themselves as slaves due to poverty had to be freed.

Insofar as these regulations have to do with the tribal allotments in the Land of Israel, they do not apply in the Diaspora, and of course there is no slavery in modern Israel.  There has been some movement among religious Jewish agriculturalists in Israel to practice Sh'mittah, but observance on this point seems to be the exception rather than the rule.

The Torah also calls for an assembly of the People at the end of each Sabbatical year, on the first day of Sukkoth,  for a reading of the Torah. Deuteronomy 31:10-13.  Although this practice was discontinued after the destruction of the Temple, the custom has been revived in modern Israel.