Praise be to Allaah.
The Prophet (blessings and peace of Allah be upon him)
connected the ruling to irrigation, and did not pay attention after that
to how the crop is harvested or what takes place before that such as
levelling the ground. This is something else that does not have anything
to do with zakaah. The Messenger (blessings and peace of Allah be upon
him) connected the ruling to something else. And the prescriptions of the
Messenger of Allah (blessings and peace of Allah be upon him) are for all
of his ummah, the first and the last of them. They are not laws that were
only for the people of his own time; rather they were for the people of
his own time and for all those who come after them until the Day of
Resurrection. Allah, may He be glorified and exalted, knew what would
happen in the future of newly-invented machines and their need for fuel
when harvesting, planting and so on.
The things mentioned by the questioner having to do with land
that is irrigated with rain water do not have any effect on the rate of
zakaah; what must be paid is one-tenth, because of the report that the
Prophet (blessings and peace of Allah be upon him) said: “On that which is
irrigated by rain, springs and the like, one tenth (is due), and on that
which is irrigated by artificial means, half of one tenth (is due).”
Narrated by al-Bukhaari in al-Saheeh; there are also corroborating
reports. This indicates that the Messenger (blessings and peace of Allah be
upon him) did not pay attention to anything done after irrigation or
planting, or anything done before that.
The ruling is based on the method of irrigation: that which
is watered by springs, rivers and rains is subject to complete zakaah of
one-tenth: one out of every ten, one hundred out of every thousand, and so
on. That which is watered by machines or by using camels or cattle to bring
the water and so on, or by sprinklers, is subject to zakaah of half of one
tenth, because of the effort and expense incurred to irrigate it. And Allah
is the source of strength.
Shaykh ‘Abd al-‘Azeez ibn Baaz (may Allah have mercy on him),