The effect is to shift the supply curve up to the left and shift the demand curve down to the left. We begin by assuming only domestic production is involved. In any given year, the supply is fixed and perfectly inelastic, a harvest is the harvest is the harvest. This raises prices and will actually increase revenue to the farmer. A bumper crop, on the other hand, will shift supply to the right, lower prices and reduce farm income.
Many agricultural commodities can be stored, that is placed in inventory.
Inventories serve to stabilize prices between growing seasons. Without inventories the above situation applies, that is a good harvest lowers prices, a bad harvest raises prices. A good harvest can be used to increase inventories, that is, not all output goes to market and price decreases are moderated. In the case of a bad harvest, inventories are sold, thereby increasing supply and reducing price increases. A price floor acts like a minimum wage.