The agency responsible for agricultural activities first became clearly evident during the Ayutthaya period (beginning in 1350 AD). This agency, known as the Department of Rice Fields, was one of the four administrative departments under the traditional tetrarchy system, which included the Department of the Capital Administration, the Department of the Palace, the Department of the Treasury, and the Department of Rice Fields. These departments were akin to modern-day ministries. Thus, in old proclamations and royal decrees, terms like the Department of Agriculture, the Ministry of Rice Fields, and the Ministry of Agriculture were used, all referring to the Department of Fields within the tetrarchy, with the title of the chief official being Khun Kasetdhradhibodi.
Later, during the reign of King Borommatrailokkanat (1448-1488), the title of the chief official of the Department of Rice Fields was renamed to Phra Kasetdhradhibodi. Subsequent royal chronicles, including the 1635 decree during the reign of King Prasat Thong, refer to the chief official as Chao Phraya Pholathep Senabodhi Sri Chaiyanopharat Kasetdhradhibodi Aphai Phiriya Borakrom Pahuh, a title that continued into the Rattanakosin period. In the Rattanakosin period, King Rama IV updated the title to Chao Phraya Pholathep Sappolsep Senabodhi Sri Phichai Rajmahayasawan Anekkanantathanyaharnphichanpathiphat Nopharatmurathathorn Mahisornsamuhachetketthadhibodi Aphaiphiriyaborakrompahuh.
The role and duties of the Department of Fields were first recorded in the comprehensive laws enacted during the reign of King Ramathibodi I (U-Thong) of Ayutthaya. These decrees included provisions assigning the Department of Rice Fields to handle and resolve disputes related to rice, crops, and draft animals, marking a significant contribution to agricultural management.
The Department's role expanded under the royal decree of King Prasat Thong, which tasked it with managing fallow lands to make them productive, overseeing irrigation and draft animals, collecting rice for royal granaries, managing royal land grants, resolving land disputes, and establishing field officers in various provinces to perform these duties. Additionally, the decree detailed nine different seals used by the chief official of the Department of Rice Fields for various responsibilities.
By the reign of King Rama V, the Department of Fields' duties included appointing officials to survey and assess the land, collecting land taxes as royal revenue, resolving land disputes, purchasing rice for the royal granaries, and supplying rice for general public.