Michigan State University Extension
Soils & Soil Management - Fertilizer - 06109725
07/10/97
N-P-K Fertilizers Extension Bulletin E-896, October 1990
by M.L. Vitosh Extension Specialist, Crop and Soil Sciences
Although it is generally agreed that fertilizers come in three physical forms (liquid, solid and gas), there are actually only two classes of fertilizers: liquid and solid. Anhydrous ammonia (NH3) is a gas, but it is classified as a liquid because it is a liquid under pressure. The term liquid fertilizer applies to anhydrous ammonia, aqua ammonia, N solutions and liquid mixed fertilizers. Liquid N-P-K fertilizers are also known as fluid fertilizer. They include true solutions which require no agitation and suspensions or slurry type mixtures of N. P and K, which require constant stirring to keep the solids suspended in the solution.
Liquid or fluid fertilizer use in Michigan has increased steadily over the last 25 years. In 1965, 9% of the total fertilizer sales in Michigan consisted of liquids. In 1988, liquid fertilizers accounted for 28% of the market. Anhydrous ammonia and N solutions accounted for 78% of the total liquids sold.
Dry fertilizers (solids) still constitute the major part of the fertilizers sold in Michigan. In 1988,92% of the total dry fertilizer was sold as bulk material, with only 8% in bags. The bulk materials are generally less expensive and easier to handle, particularly when large quantities are used. Urea is the most popular source of dry N fertilizer, accounting for 79% of the total dry N used. Ammonium sulfate has risen in popularity. In 1988 it constituted 14% of the dry N market. The use of ammonium nitrate has decreased greatly in recent years, although it is a very good source of N.
Crop responses to liquid and dry fertilizer are similar, provided the same amounts of plant nutrients are applied and the same placement and water soluble P materials are compared. Reactions of these materials in soils are similar. When placed in the soil, dry fertilizers absorb water and undergo chemical reactions similar to liquid fertilizers.
Price per unit of plant nutrients, application costs, potential for leaching, ease of handling and customer service are the palms factors to consider when buying fertilizers.