CHEMICAL SOURCES OF NITROGEN
Ammonia (liquid ammonia): This is perhaps the most widely used of all nitrogen fertilizers today, yet is of no practical value to the home gardener because special apparatus is needed to apply it. It is mentioned here only because many gardeners ask about it after reading accounts of its use in agriculture. These liquids run about 30 per cent ammonia, of which about 85 per cent is nitrogen.
Ammo-Phos (ammonium phosphate): There are two commercial grades of this material. Grade A contains 11 per cent nitrogen and
48 per cent available phosphoric acid. Grade B contains 16 per cent nitrogen and 20 per cent phosphoric acid. Both are excellent sources of completely soluble nitrogen and phosphorus.
Ammonium Phosphate: There are two grades: monoammonium phosphate contains 11 per cent nitrogen and 60 per cent phosphoric acid while diammonium phosphate analyzes at 23 per cent nitrogen and 53 per cent phosphoric acid. Both are completely soluble. Beware of using them on rhododendrons and other acid-loving plants, however, as they are quite alkaline in reaction.
Ammonium Suljate (sulfate of ammonia): Once the leading source of nitrogen in chemical fertilizers, it is still #1 on the home gardener's list. In the agricultural field its place is being taken over by liquid ammonia. Sulfate of ammonia contains about 20 per cent nitrogen. It can be applied dry but must be watered in immediately to avoid burning. It is much safer if first dissolved in water.
Sodium Nitrate (nitrate of soda): This was one of the first chemicals used as a fertilizer. Vast deposits of sodium, combined with oxygen and nitrogen, were found in Chile, and were worked for fertilizer purposes during the nineteenth century. Because it was for many years the leading source of chemical nitrogen, it is firmly entrenched in the literature of gardening. It is often recommended out of habit when other materials would be safer and better. Sodium nitrate may have some use in strongly acid soils but will deflocculate clays and make them greasy if used too often. It is not an ideal source of nitrogen and other materials should be substituted if possible.
Urea: Discovered originally in urine, this is now produced synthetically in large quantities. Urea is not a protein but because it contains a carbon particle, it is classed as an organic compound, to the consternation of organocultists. While not instantly available, urea goes through fewer stages to break down into nitrate form, hence starts feeding a little more rapidly than do organic products.