Urea based fertilizers could be harmful to insect life (e.g. it's the active ingredient in "SB Plant Invigorator"). It's also worth noting that the fertilization for mono-crops is detrimental to diverse plant ecologies - native orchid species in the UK have been decimated due to fertilizer run off from agriculture - lots of other species native to low nutrient chalk downland are also effected. The knock on is dramatic decreases in insect populations and diversity, butterflies have been hit especially hard.