In West Texas, Cotton Has Become an Important Crop in the Last

In west Texas, cotton has become an important crop in the last several decades. However, in this hot, dry part of the country there is little rainfall, so farmers irrigate their cotton fields. They must also regularly fertilize the cotton fields because the soil is very sandy. Figure 37.2 shows the record of annual productivity (measured in kilograms of cotton per hectare of land) since 1960 in a west Texas cotton field. Use these data to answer the following questions.

Figure 37.2
-Based on the information provided above, what is the most likely cause of the decline in productivity?

A) The farmer used the wrong kind of fertilizer.
B) The cotton is developing a resistance to the fertilizer and to irrigation water.
C) Water has accumulated in the soil due to irrigation.
D) The soil water potential has become more negative due to salination.
E) The rate of photosynthesis has declined due to irrigation.