In contrast, the organic fertilizers are more likely to have significant amounts of micronutrients, and the macronutrients are likely to be in forms that are not as readily absorbed. A potential drawback of organic fertilizers is that they may not release enough of their principal nutrient at a time to give the plant what it needs for best growth. Because organic fertilizers depend on soil organisms to break them down to release nutrients, most of them are effective only when soil is moist and the soil temperature is warm enough for the soil organisms to be active. Microbial activity is also influenced by soil pH and aeration. The use of organic fertilizers increases the soil's organic matter content and improves the soil's physical structure.
Inorganic fertilizers can be one of the major sources of groundwater pollution.
The nitrogen is in such a soluble form that it tends to leach from the point of application. Water-soluble chemical fertilizers will injure plants if not washed or brushed off the foliage. Slow-release fertilizers are less susceptible to leaching and are preferred on sandy soil types, which tend to leach. Various salts and minerals can serve as fertilizer materials. Examples are ammonium sulfate, potassium nitrate, super- phosphate, potassium chloride and potassium sulfate.