Solar ovens are handy for sterilizing organic fertilizer mixes in relatively small quantities. The simplest version is just a box lined with black absorbant material (not plastic, it might melt) with a glass plate on top, and orient towards the sun around noon for a few hours. Test it for sufficient heat generation for sterilization purposes by seeing if a metal cup full of water starts boiling.<p>Even then you should wear an decent mask when handling all fertilizers, you don't want to be breathing the dust regardless of whether it's synthetic or organic fertilizer.