Fertilizers, solid, physical properties

Fertilizers are packaged in a variety of different forms including solids, liquids (solutions and suspensions), and gas (anhydrous ammonia). The important physical properties of solid fertilizers are particle size, particle strength, caking tendency, chemical stability, and hygroscopicity. 

In the following section, most of the physical properties of solid fertilizers will be discussed. 

There are a number of other physical properties of solid fertilizers which are of importance for various reasons. These physical properties are briefly discussed below. 

Urea, a highly water-solnble white crystalline compound, has by far the highest nitrogen content among solid fertilizer compounds (46.6%) as noted, its commercial synthesis was introduced by BASF in 1922 (fig. 7.1). Its good physical properties and lack of fire and explosion hazards make it the most commonly used solid nitrogen fertilizer, while liquid urea is commonly used in nitrogen solutions, and the prilled compound is a common part of mixed fertilizers. 

Physical and Chemical Properties. Ammonium nitrate is a white, crystalline salt, dj° = 1.725, that is highly soluble in water, as shown in Table 3 (7). Although it is very hygroscopic, it does not form hydrates. This hygroscopic nature compHcates its usage in explosives, and until about 1940, was a serious impediment to its extensive use in fertilizers. The solid salt picks up water from air when the vapor pressure of water exceeds the vapor pressure of a saturated aqueous ammonium nitrate solution (see Table 4). 

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