Fertilizers for soil on which plants grow come in a variety of forms, such as organic, inorganic, single nutrient, double nutrient, complete fertilizer (contains N, P, and K in that order), speciality fertilizers, composts, and manures. Information about each of these forms follows. Most of the N used in fertilizers is derived from a synthetic process developed by Europeans called the “Claude-Haber process.” This process uses nitrogen gas (N2) from the atmosphere along with hydrogen gas (H2) from natural gas in a device where pressure can be increased and temperature can be raised. The reaction is accelerated using an iron catalyst and removing the product (NH3) as it is formed. The Fe catalyst is subject to poisoning from impurities, such as As, Co, P, or S. Anhydrous ammonia has the highest percentage of N and the cheapest per unit of N since no processing is involved. Anhydrous (without water) ammonia is a gas but when compressed changes to a liquid. For application to soils a pressurized tank is required with a device to inject the liquid ammonia into the soil. Upon release of pressure, the liquid changes back to a gas; however, the ammonia gas reacts with the moisture in the soil to form NH4+ that is available for plants. One problem with ammonia is that NH3 gas is toxic to seedlings and growing plants, so must be applied prior to planting. This limits its use for landscape projects. Salt solutions of aqua ammonia are obtained by dissolving ammonia gas, ammonium nitrate, or urea in water. The amount dissolved will vary the concentration of N in the final product. This can be used in landscape projects, but care must be used as this material can salt out and plug up orifices when sprayed onto a soil. There is no real difference between liquid or solid fertilizers, provided the percentage of N is the same. Ammonia Nitrate [NH4NO3] (33.5% N) Ammonium nitrate is formed by ammonia gas reacting with nitric acid: . . . NH3 + HNO3 → NH4NO3 . . . This material is hygroscopic (absorbs water from the air) and requires moisture-proof bags for storage.
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