i think the supply curve shifts to the left for the agricultral product diagram, it did say in the article that less land will be used for agricultral products thus supply shift to the left, result in increase in price and fall in quantity. If you shift the demand curve, even though it raises price levels, it would show an increase in quantity of agricultral products, but this was not the case, it never said there was going to be an increase in demand as well for the products.
Im not sure though..