The dilution factor of 55.6 is the overall dilution of the sample (after extraction) throughout the Standard Assay Procedure of K-PHYT (Part A step 2, and Part B).
In Part A Step 2 the liquid sample is diluted by a factor of 2 whereby 0.5 mL of sodium hydroxide solution (0.75 M) is added to 0.5 mL of the extract supernatant.
In Part B 0.05 mL sample from Part A is used in a total reaction volume of 1.39 mL therfore in this step the sample is diluted by a factor of 27.8.
The total dilution factor of the sample therefore is 55.6 derived from 2 (Part A) multiplied by 27.8 (Part B).