Following the commandments of God requires faith and commitment. While God forbids them to plough the land on Sabbath Year(shemiṭṭah), God also promised them to bless abundantly on the sixth year.
You may ask, “What will we eat in the seventh year if we do not plant
or harvest our crops?” I will send you such a blessing in the sixth
year that the land will yield enough for three years.
(Leviticus 25:20-21, NIV)
This is the same case for Tithe. While giving 10% of our income to God may seem to be a lost, we are actually gaining. All we have to do is test Him in this.
Bring the whole tithe into the storehouse, that there may be food in
my house. Test me in this,” says the Lord Almighty, “and see if I will
not throw open the floodgates of heaven and pour out so much blessing
that there will not be room enough to store it. I will prevent pests
from devouring your crops, and the vines in your fields will not drop
their fruit before it is ripe,” says the Lord Almighty. (Malachi
3:10-11, NIV)
It was also not easy for the Jews who settled in Palestine during the Zionist movement to observe the Sabbath Year but they somehow managed to observe it.
Since the Zionist movement began to encourage agriculture in
Palestine, the observance of shemiṭṭah has become a problem for
solution. The leaders of the movement, who had the interest of the
colonists at heart and feared that the shemiṭṭah might jeopardize
their existence, claimed that the law is now obsolete. (source)
There are also some practical stories where those who observed the Sabbath Year were blessed miraculously.
Haredi Jews tell stories of groups of Israeli Jews who kept the
Shmitta and experienced remarkable agricultural events which they
describe as representative of miracles in fulfillment of the Biblical
promise of bounty. One famous story is told about the
then-two-year-old village of Komemiyut during the 1952 Shmittah. The
village was one of the few who refrained from working the land that
year. At the end of the Shmittah, farmers searching for seed to plant
found only wormy, inferior seed that had been rotting for years in an
abandoned shed. Rabbi Binyamin Mendelson advised them to sow this seed
anyway, saying "The Almighty who causes wheat to sprout from good seed
will bless your inferior seed as well," even though it was three
months after neighboring villages had planted their fields. They did.
That year the fall rains came late, the day after the Komemiyut seed
was sown. As a result, the neighboring villages had a meager harvest,
while the village of Komemiyut, who sowed from the old store, had a
bumper crop. (source)
As for the 49 or 50 years cycle, Jewish Encylopedia says
There is a difference of opinion in the Talmud as to whether the
jubilee year was included in or excluded from the forty-nine years of
the seven cycles. The majority of rabbis hold that the jubilee year
was an intercalation, and followed the seventh Sabbatical year, making
two fallow years in succession. After both had passed, the next cycle
began. They adduce this theory from the plain words of the Law to
"hallow the fiftieth year," and also from the assurance of God's
promise of a yield in the sixth year sufficient for maintenance during
the following three years, "until the ninth year, until her fruits
come in" (Lev. xxv. 22), which, they say, refers to the jubilee year.
