P and K cycles

From looking at the N cycle again I would say fixation doesn't always render plant nutrients unavailable. I can see there is another input arrow for photochemical fixation (NHO3) that goes directly into the nitrate pool. My understanding is that atmospheric N compounds are fixed into NHO3 and when they enter the soil solution, they dissociate, releasing a proton and forming NO3- which is plant available. Is that correct? In more general terms, is any kind of N fixation that's labelled as an input described as the conversion of atmospheric N to an ionic, reactive form of N such as nitrite, carried out by soil organisms?

What Sandra was hinting to is the process of ammonium (NH4+) fixation that traps (or fixes) ammonium ion in the inter-layer spacing of certain phyllosilicate minerals. Through that process of ammonium fixation, ammonium ions from soil solution (where they are available to plants) are made unavailable to plants.