As Seth points out from his observation keeping worms, the worm poop dissolves in water. Does that mean that all the nitrate that is in it becomes instantly available? Yes, that it is why it is ready to use as an immediate fertilizer. Now its second other virtue: that not all its fertilizer potential is immediately released. At least half of it are nitrogen compounds that are bound /stuck onto clay particles. When one dissolves clay in water, it doesn't actually dissolve it stays suspended. It is when fresh water looks murky. Our naked eye cannot distinguish those particles because their diameter is below what an even very fine sighted person can recognize. These clay particles that came out of the worm are covered in nutrient rich compounds. These compounds still become food for free roaming microbes and more nitrate is generated. This second attribute is the slow release mechanism that I pointed out earlier.
Now I would like to underline when I say the word salt I'm using it as understood in a chemistry class: a compound molecule that has a negatively charged ion ( NO3 nitrate) and a positively charged ion (K potassium). I'm not referring to the word as table salt which is one other chemistry salt (sodium chloride), which can be worrisome in high contents. The molecule that is taken up around the root membrane is the ion nitrate or the ion potassium. Not the complete salt. These now separate ions go through separate pathways during the osmosis mechanisms.. When soluble salts dissolve in water, their ionic parts swim in the solvent (water) freely... no longer bound together. So if the plant needs more nitrate than potassium then it will draw just nitrate and the rest is left in the liquid outside the membrane. One other source of nitrogen is ammonium NH4, which is positively charged. In all cases the nitrogen is needed for the synthesis of proteins. These are actively being generated using the energy stored in the sugars produced by photosynthesis. If the plant doesn't have enough nitrogen available as nitrate or ammonium, then it can't produce proteins ( which are chains of aminoacids). It can't develop its tissues and thus it can't grow, in spite of having light with which it can still store up energy. This said as plainly possible. In any living green plant all of this happening at the same time. Actively growing areas of plants are its buds, or root tips and also the cambium or green tissue that is placed as a ring just slightly under the bark. The leaves also harbour a lot of protein while the core of a cane is solely dead tissue. Very similar to our bones that are composed of dead tissue with calcium phosphate deposits that make bones sturdy. The equivalent of that in plants is cellulose ( a sugar compound). In woody plants ( roses i.e) tannins are added that make that part indigestible to herbivorous predators. Imho, unless one gets a clear understanding how everything works its very difficult to find the right measure of things and know what is needed and how much of each.. I only concentrated around one of the macronutrient needed: nitrogen. Each other nutrient has its own pathway and cycle. Some are needed in very small ammounts: trace elements.
Arturo
