What is the difference between the mobility of nitrogen and phosphorus in soils ?
Soil nitrogen can exist as a structural part of plant residue or humus 5 (organic nitrogen), as ammonium (an inorganic cation 2 soluble in water) or as nitrate (an inorganic anion 2 soluble in water). Soil phosphorus can also exist as a structural part of plant residue or humus (organic phosphorus), as phosphate (an inorganic anion soluble in water) or as insoluble 3 phosphate minerals. Ammonium nitrogen is not very mobile because it is strongly attracted to negatively-charged clay surfaces. Phosphate reacts with the soil, forming insoluble phosphate minerals that are inaccessible to plants and immune to leaching. Nitrate, however, is not attracted to clay surfaces and does not form insoluble minerals, leaving it dissolved in water and easily leached by water percolating through soils.
