In order to test the effect of a certain brand of fertilizer, Lao Zhang divided his own paddy field into the east and the west, and fertilized the land in the east, without fertilizing the west. After the rice was harvested, the yield in the east land was 700 kg per mu, and the yield in the west land was per mu.400 kg. Therefore, this brand of fertilizer can effectively increase production. Which of the following can best refute the above argument? ['The soil fertility of the eastern plot is originally higher than that of the western plot.', 'Both the east and west fields are planted with the same variety of rice.', 'Pests on the eastern plot have been pest-infected.', 'Lao Zhang harvested rice in the western plot before the eastern plot.']