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It is labeled Diammonium Phosphate.
Could be low biuret, but if the product label does not list the biuret content there is no way of knowing. If you can't find any I could send you a 5-lb. jar of low biuret urea (0.5% biuret).
My best guess either the spray was over applied, sprayed in the heat of the day, or not a low biuret variety