All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
All the scholars do not necessitate a complete year for Zakat to be paid on crops but the majority of scholars necessitate the minimum amount liable for Zakat on crops, contrarily to Imaam Abu Haneefah who does not think that it is an obligation to reach the minimum amount liable for Zakat. Their evidence is the narration: "There is no charity on less than five Awsuq.(plural of Wasq: One Wasq is equal to sixty Saa' and one Saa' is equal to 2480 grams)." [Al-Bukhari and Muslim]
Imaam Abu Haneefah bases his opinion on a rule which states that restrictions or specifications abrogate what has been instituted before and the Sunnah does not abrogate the Qur'an, that's why he did not apply the narration reported above.
In conclusion, we draw the attention of the questioner to the following matters:
Firstly, no scholars set a condition of a complete year on cultivations as previously stated.
Secondly, the scholars stated that the elapse of a complete year is necessary for Zakat on livestock, money and tradable items; Zakat have to be paid on these every year as it is subject to growth. The other evidence is the narration of the Prophet narrated by 'Aa'ishah as he said: "There is no Zakat on wealth unless a complete year elapses on it. As regards grains and fruits, Zakat is obligatory on them only once even if their owner stocks it for ten years as long as he did not buy it to trade with it, as in this case it is a tradable item."
Allaah knows best.