Answer: D. experimental bias
Step-by-step explanation:
An experimental bias is the condition in which the experimenter manipulate the experimental procedure, equipment and even the results so as to obtain the desired outcome.
The given situation is an example of experimental bias this is because of the fact that field A was supplied with old fertilizers and brand new irrigation system but field B was supplied with new fertilizers and irrigation system which will be repaired in next season. Hence, a experimental bias is done so as to show that the old fertilizer is better than the new one.