It seems to me that the only thing being tested here is the two different farmers.
When you get a question like this, you want to look for a single changing variable. If there are several changing variables, the experiment is going to be inconclusive. If there are no changing variables, you have no purpose to experiment. We can see that both farmers have the same setups. Each has two identical sets of four plots with the different types of farming methods. Every plot of land is being treated the same with identical doses of fertilizer prior to the test starting, and the crops grown are genetically identical. The only thing changing between cases here is the farmer's land. One might be in a mountainous area with rocky soil and dry climate. The other might be on a coastal plain with high salt content and intense heat and humidity. These two variables being tested are the root of the problem.
I would say that the thing being tested is the climate of the two farms in order to determine the most viable method of agriculture for them.