In the two corn fields in the East and west of the village, the land in the East is fertilized with calcium superphosphate, while the land in the west is not. As a result, the yield of corn per mu in the East is 300 kg and that in the west is only 150 kg. 
Each plot is planted with four different kinds of corn.
 the reason why the land in the East is higher than that in the west is due to the application of calcium superphosphate.