Chemical application equipment and combines aren't used for farming wheat but maybe two weeks out of the year apiece. It just simply isn't feasible to own a piece of equipment that spends almost 50 weeks a year in the shed. The windows for spraying and harvesting are only about 2 weeks out of the year apiece. It would be different if a person farmed multiple crops. Farmers in some areas can grow wheat, corn, milo, and soybeans. Corn, milo, and soybeans require more attention than wheat, so the sprayer sees a good bit more use. The harvest on all of those crops can also fall at different times, and some have a wider harvest window than wheat, so the farmer can get a couple months use of the combine, not just a couple weeks. In those circumstances, a person might be able to justify keeping a sprayer or a combine. Otherwise, those two types of equipment depreciate too fast and cost too much to maintain to justify even a fairly cheap used machine.
A tractor, plow, and drill is a different story. A tractor on that same wheat acreage is going to see several months use. Mine will have seen use on my wheat ground from May to October this year. Also, those types of used equipment have few moving parts, so buying a used one isn't really a problem. Lots of good tractors out there with 10,000+ hours on them and still going strong. I used to run one of my uncles that had nearly 24,000 hours on it when he sold it.
Another benefit to hiring chemical application and harvesting done is technology. A new machine will really clean the wheat, and it will put almost all of it in the bin. The older and more used a machine gets, the more it loses. Plus it is harder to get the machine set right and there are fewer instruments to help guide the adjustments. Often times buying an older combine and cutting wheat looks cheaper on paper. But when you figure up what you are losing out the back that should be going in the bin, it isn't. Same with spraying. Chemicals and fertilizer are very expensive. A nozzle putting out too much here or there, or a little overlap here or there can get expensive in a hurry. A custom applicator with everything working correctly and a good GPS unit can often completely offset the expense of the application simply through efficiency.
