How does the switch rate work?

The Switch Rate is an optional box within the Fertility tab, below is example to explain the function. 

• Here is are starting field with no Max, Min or Switch rate applied, the areas of interest are the Purple Squares with values hovering around zero and the Blue rounded squares with values in the mid-60's:

• Setting a switch rate tells the system how to handle calculated values that would have landed between the minimum rate and 0.  For example, if the minimum rate is 80 lbs per acre, and the switch rate is 60, then everything calculated that is larger than 60 and less than 80 will be set to the minimum rate, and everything smaller than 60 will be set to 0. With this setting applied our Purple Square area has gone to Zero, while the Blue Squares have gone to the new minimum rate of 80.
• To enforce minimum rate as the absolute minimum (eliminating all 0 application areas) for the entire field, set the switch rate to 0. Note: the Purple and Blue areas discussed above have been driven up to the new minimum for the field of 80. 
•  Leaving the switch rate blank will set every area with a calculated output lower than the min rate to 0. Since our purple and blue areas values fall below the 80lbs/ac minimum the resulting output is Zero product in that area.