Royal Ploughing Ceremony - May 13

In the Royal Ploughing Ceremony on the 13th of May two sacred oxen are hitched to a wooden plough and they plough a furrow in some ceremonial ground, while rice seed is sown by court Brahmins. After the ploughing, the oxen are offered plates of food, including rice, corn, green beans, sesame, fresh-cutgrass, water and rice whisky.

Depending on what the oxen eat, court soothsayers make a prediction on whether the coming growing season will be bountiful or not. The ceremony is rooted in Brahman belief, and is held to ensure a good harvest.

Sometimes the monarch himself has taken part in the ceremony!! After the Ceremony, onlookers swarm the field to gather the seed, which is believed to be auspicious. 

Note: this text and photo is from Wikipedia and from Thailand Travel Online