A.) you are expecting farmers to be quants,
B.) There are 10000 more inputs to farming than what you described. Labor being a major one.
Financier:
"Well Jim, I know you were focused on digging the irrigation for your farm but with 'Free Money' in the economy, valuations for real estate and other commodities were going to rise. The Delta's on your futures were all out of wack!"
Jim:
"What's a delta?"
- Diesel for tractors
- Fertilizers
- The weather itself
- interest rates
- real estate
AFAIK the only inputs without derivatives are labor cost and pesticides.