What is the required Zakah (Ushr) rate for crops irrigated without effort or expense?

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The obligatory Zakah (Ushr) rate is one-tenth (Al-Ashr) for crops irrigated without requiring expense or labor, such as those watered by rainfall (Samaa') or natural springs ('Uyun), or those whose roots reach easily accessible groundwater ('Athari). This established ruling is supported by Malik, Al-Thawri, Al-Shafi'i, the Ahl al-Ra'y, and others. The primary evidence is the Prophetic saying: "For what is irrigated by the sky and springs, or is 'Athari, is one-tenth (Al-Ashr), and for what is irrigated by drawing water (Nadhl) is half a-tenth (Nisf al-Ashr)." This hadith is narrated by Al-Bukhari. Another supporting narration from Mu'adh states that the Prophet commanded taking one-tenth for what was irrigated by the sky or by 'Ba'l (natural means), and half a-tenth for what was irrigated by a bucket (Daliyah). 'Ba'l' refers to that which is watered by its own roots without added irrigation.