You take out a loan to get you through to harvest, then you pay it off when you sell your crop.
As far as insurance goes - there are certain things that dont qualify for a payout. Generally speaking, a bad crop year isnt grounds for your insurance paying out. Having your crop hailed out or high winds completely destroy it is grounds to have insurance pay out, given that at least x% of the crop was destroyed. This also varies on if you insure each field, or if you insure your crop as a whole (one field may be a total loss, but the rest of your crops 2 miles away may be fine). If you insured each field, insurance will pay out on that field. If you decided to save money and insured your crop/farm as a whole, you likely wont get a payout because not enough was a total loss (and keep in mind that it's not a 100% payout - commodity prices change daily)