Michigan State University Extension
Soils & Soil Management - Fertilizer - 06209706
07/10/97
Fluid Fertilizers--Liquids and Suspensions MSU Ag Facts Extension Bulletin E-933, December 1984, Revised, destroy previous editions
by R. E. Lucas and M. L. Vitosh, Department of Crop and Soil Sciences
All fertilizers can cause injury to plants when applied in excess. Unless diluted with water, most liquids of comparable formulation are as toxic as dry fertilizers. The extent to which fertilizers can burn plants can be easily evaluated by their "salt index," which compares them with an equal weight of sodium nitrate.
Liquid fertilizers made specifically for application to the foliage of plants, to seed or to household plants should have a low salt index value. Double nutrient salts, such as ammonium phosphate and monopotassium phosphate, help keep the salt index down. Additional information about types, uses and characteristics of fertilizer can be found in Michigan State University Extension bulletin E-896. ==================================================== Table 1: Salt index for some common fertilizers.
Salt Salt Index* --------------------------------------------------- potassium chloride 116 ammonium nitrate 105 sodium nitrate 100 urea 75 potassium nitrate 74 ammonium sulfate 69 calcium nitrate 65 potassium sulfate 46 diammonium phosphate 34 monoammonium phosphate 30 superphosphate (0-46-0) 10 monopotassium phosphate 8 --------------------------------------------------- *From Rader et. al., Soil Sci. 55:201-218. ====================================================