Prince Charles received the highest grade of the Order in 2017:

https://www.instagram.com/p/BRtHMr1Byze/?utm_source=ig_embed

https://twitter.com/ClarenceHouse/status/842400912891080705/photo/1

Unlike the two National Orders (Legion of Honour and Order of Merit), which have five ranks (up to the Grand Cross), the Order of Agricultural Merit is only a Ministerial Order, headed by the Minister of Agriculture. As such it has three ranks (Knight, Officer, Commander).

I believe that Princess Caroline of Monaco is also a recipient of the Commander's cross.

A bit of trivia: at the time of the order's creation, in 1883, it was widely mocked by the press and society (because of its overly prosaic nature), and nicknamed 'le poireau', that is, 'the leek'!