When oil prices go up, gas and diesel prices go up. When those prices go up, the cost of farming grains (especially corn) goes up.   When there are droughts, floods, hail damage, etc, the supply of grains goes down - making the demand go up, and the price go up.
You can pretty much track grain prices right behind oil prices - you need to put gas in a tractor to make it run, and fields are fertilized with nitrogen that is cracked from natural gas. So a lot of it depends on oil and natural gas pricing.