In addition, the "Seedists" should also have to explain the following.
The pallets appear in late fall and disappear in early spring according to the OP. What crops are planted in the late fall? Depending on how you define "late," only small grains and canola come to mind amongst the agronomic crops. Amongst horticultural crops, beets, broccoli, carrots (AKA carets), kale, peas, and spinach come to mind.
1. The OP provided us with photos of the pallet formations as of late December. Would we not expect to see some evidence of the germination and growth of fall-planted crops (either agronomic or horticultural) in those photos?
2. Why would farmers wait until spring to retrieve the pallets and thus do damage to fall-planted crops?
3. In my experience, a relatively small amount of seed is required relative to acreage. This is especially true for some of the horticultural crops. What crop uses a seeding rate that would require two pallets of seed every 500-700 feet?