One slightly contentious area of growing organically is just what fertilisers can be used. There are purists who stipulate only plant based materials, no animal products such as bonemeal or hoof and horn, nor any mineral salts since these are mined.
So tip-toeing through my garden is proving problematic. Easy enough to compost my vegetable peelings, lawn mowings and leafy trimmings. My comfrey patch is not yet established to provide sufficient liquid feed. But my citrus trees in containers were looking decidedly unhappy with yellowing leaves, which I diagnosed as a lack of iron, a vital trace element. Remedied by dosing with sequestered iron - chemically altered iron (chelated) to make it more accessible to plants. Is it still organic?
Very contrary opinions abound - in small garden plots, trials have shown little or no difference in yields whether using organic or inorganic fertilisers. Animal by- products have caused concern over the years with BSE, anthrax and the like. Animal manures must be composted and can introduce weed seeds as these are not digested. Applying a solution of epsom salts is promoted as a cheap and quick way of greening foliage if there is a magnesium deficiency. A naturally occurring mineral, again not derived from plant or animal source.
I think I'll stick with my hot-bin for the time being and nurture my comfrey patch for home grown foliar feed, at least I know what's going on.
PS - my citrus trees are much greener so I may have to adjust my philosophy for containers. Long term all the available nutrients in the soil are absorbed or leached out which then need replenishing.