The portion of slow-release nitrogen is listed on the fertilizer
bag as water-insoluble nitrogen (WIN).
If no WIN is listed on the fertilizer label, assume that all of
the nitrogen is water soluble or quickly available unless the nitrogen
includes sulfur coated urea.
Sulfur-coated urea fertilizers provide slow-release nitrogen, but
the fertilizer label does not list it as WIN. If the fertilizer
contains sulfur-coated urea, include that portion as part of WIN
when determining the percentage of total N that is slowly available.
Water-insoluble types of fertilizers release nitrogen over time.
They are often applied at higher rates and less frequently than
quick release formulas. The initial response of turf is slower than
quick release types but these materials continue to provide nutrients
over a period of 8 to 10 weeks or more. They will not burn the turf
even if applied at high rates and are not prone to leaching.