Here's a problem to solve: A farmer plants corn in a field every year for several years. Each year he notices that his production of corn per acre has decreased even though the weather conditions have been very similar. A change in which abiotic factor is most likely causing the decrease in the production of corn?

Among the 4 following options, which is the correct answer?

- A: decrease in soil nutrients
 
- B: increase in precipitation
 
- C: increase in wind speed
 
- D: decrease in sunlight
 