Lao Zhang in order to experiment with the effect of a brand of fertilizer, the rice fields divided into east, west two pieces, in the east of the plot fertilization, the west of the plot does not fertilize. After the rice harvest, the eastern plot yields 700 kg per acre, and the western plot yields 400 kg per acre. 
Lao Zhang first harvested the rice in the West plot and then the rice in the East plot
 the fertilizer of this product can effectively increase production.