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. The figure below 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.

-If you were the county agriculture agent, what would be the best advice you could give the farmer who owns the field under study in the above figure?

A) Plant a variety of cotton that requires less water and can tolerate salinity.
B) Continue to fertilize, but stop irrigating the field and rely on rainfall.
C) Continue to irrigate, but stop fertilizing the field and rely on organic nutrients in the soil.
D) Continue to fertilize and irrigate, but add the nitrogen-fixing bacteria Rhizobium to the irrigation water until the productivity increases.
E) Add acid to the soil and increase its cation exchange capabilities so more nutrients are retained in the soil.