The reason why James chose the soy field was because of its fertile and soft soil. If he was going to dig a large portion of the land, he had to choose a section with few rocks and no deep roots to contend with. This is why he was so surprised to hit something large and hard in the soft earth of this patch of land.
James’ curiosity urged him to jump out of the machine he was using and see the object close up. Once near, he used his bare hands to dig the soil until he felt a smooth yet hard object in the ground. He knew it wasn’t a tree root or a stone because he had never felt anything like it.