According to the economic law of supply and demand, prices fluctuate based on supply and demand. The price of a good or service goes up if demand is greater than supply. Or if supply is greater than demand, the price goes down.
According to the economics of supply and demand, what is most likely to happen if the Brazilian soybean crop is one of the best ever?
The price of soybeans will go down in Brazil.
The supply of soybeans increases (while demand stays the same) so the price goes down. Then, at the lower price, there is increased demand for soybeans. There is not enough information to determine if Brazilian farmers will earn more or less money. That depends on how much the price falls.