Is it not at least partly due to water? If it's blow sand, maybe the early planted stuff didn't get the right rains? Later you had more rain and it kept it alive. 

There is blow sand here that will not grow a corn or bean crop unless it's irrigated. If it's watered (and fertilized) it'll grow a crop as good as the "good dirt". No water though = no crop in the corners and other areas 

Or the lack of water making certain nutrients unavailable