Salt Index

Salt index is the ratio of an increase in osmotic pressure produced by a fertilizer compound compared to a standard sodium nitrate base.  The higher the salt index, the more concern there is that the fertilizer material can affect the germinating seed.  The following table shows salt index for some common starter fertilizers.

                       Table 1                                  Salt Indexes_________________________________

  Product_                           Source of Potassium                             Salt Index

6-24-6                                           K0H                                                      11.5 

9-18-9                                           K0H                                                      16.7

10-34-0                                         —–                                                       20.0

7-21-7                                           KCL                                                      27.8

4-10-10                                         KCL                                                      27.5

7-18-6-2s-.5zn                            KCL                                                      29.0
4-10-10-1s-.25                           KCL                                                      29.0___________________

Sources:  C.A.M Laboski:  2008 Wisconsin Fertilizer, Ag Lime, and Pest Management Conference

                 RH Tinsman Jr.