Ganbare Noukyou Seijo - Seijo no Chii to Konyakusha wo Ubawareta Reijou no Nougyou Kakumei Nisshi

'Save your people with your charity and knowledge, and be a source of comfort to them.'
Alicia, the daughter of the next saint, has kept the words of her predecessors and has worked hard to improve her knowledge. Her efforts are in vain when her twin sister suddenly loses both her position and her fiancée. All she has left is a tattered book on agronomy.
In the midst of her disappointment, she accepts a marriage proposal in a faraway land, only to be asked by the beautiful Roland to rebuild his estate...….?
A fantasy about the birth of a saint, in which a strong and foolish farmer's daughter saves her country with her overwhelming agricultural knowledge!

(Source: MangaDex)