As a result of implementing an experimental farming system that combined aggressive new fertilization, deep irrigation, and speculative pesticides, the yield on crops at a farm in central California grew consistently and considerably over the past six years. However, yields this year unexpectedly plummeted, causing the farm's owners considerable financial difficulties.
Which of the following statements, if true, best explains the unexpected drop in yield?
A) As a result of a serious and recent economic recession, the market for the products the farm produced shrank in size during the past year.
B) Other farms that began using the experimental system at about the same time also reported an unexpected plummet in yields this year.
C) The central California region where the farm in question is located experienced a drought 9 years ago, 3 years ago, and this past year.
D) A different experimental system, used on a different crop, failed after two years at a farm in Iowa. Scientists later discovered that chemicals involved in this different system slowly poisoned the soil.
E) Significant and sustained increases in agricultural productivity eventually lead to an exhaustion of important nutrients in land.