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.
Rice is among the crops that are liable for zakah if the conditions for paying zakah are met: the harvest reaches the Nisaab (minimum amount liable for zakah), and the amount of zakah differs if the land is irrigated by rainwater or waterwheel. Imaam An-Nawawi said, "Zakah is due on each crop that is produced by the land, is used as basic food, can be stored, and is cultivated by humans, such as wheat, barley ... and rice..."
Basically, zakah on crops and fruits is given out from the harvest itself, not from its price, provided that the harvest reaches the Nisaab of zakah. Hence, you should pay the zakah from the rice itself. According to the majority of scholars, it is not sufficient to pay zakah from the price or value of an item except in case of trade goods. We have mentioned the ruling of zakah on crops and fruit, their Nisaab, and the difference between crops watered by irrigation and by rainwater in fataawa 29066 and 89186.
The expenses of irrigation are not deducted from the zakah on the rice; the majority of the scholars, namely the four main schools and others, hold that the expenses of farming are not deducted from the zakah. An-Nawawi said, "Our companions held that all the expenses incurred, such as expenses for harvesting, drying (dates), storing, cleaning, transporting, and others are to be borne by the owner from his money, and nothing of it is deducted from the (total) amount of zakah, and there is no disagreement among scholars in this regard." [Al-Majmooʻ]
Ibn Qudaamah said, "All of the expenses of farming incurred until the zakah is paid on the harvest are to be borne by the owner, because fruit is like cattle in this regard. The costs of fodder and herding cattle until zakah is paid are to be borne by their owner." [Al-Mughni]
If the harvest does not amount to the Nisaab, then zakah is not paid for it. If the owner sells the harvest and its price amounts to the Nisaab by itself or when added to his other items of property (money or gold or silver) and a lunar year passes by, then zakah is payable. In this case, the owner should pay 2.5 % of the total wealth.
Allaah knows best.