FieldScience
>> Left: Figure 12a. Calculating the Size Guide Number and Uniformity Index of a Fertilizer. Right: Figure 12b. Testing for Fertilizer Granule Segregation.
termining how consistent the diameter of granules within a bag or lot of fertilizer is. To calculate the UI, the size of the sieve opening in millimeters that retains 95% (or passes 5%) of the sample is di- vided by the size of the sieve opening that retains 10% (or passes 90%) of the sample. This fraction is then multiplied by 100. For example, a fertilizer with a uniformity index of 50 contains a range of variable-sized particles with the average small particle being one- half the size of the average large particle. The average smallest size granule in a fertilizer with a UI of 33 is one-third the size of the largest particle. Sports turf fertilizers often have a UI of 40 or more. Granule Segregation Test. One way to observe the variation in
the relative size of granules in a fertilizer is to construct a box 24 in. long, 2 in. wide and 18 in. high from clear plastic (for ex- ample, Plexiglas) and wood, and perform a granule segregation test (Figures 12a and b). When fertilizer is poured through a funnel positioned just above the top left corner of the box, larger and heavier gran- ules move further to the right than smaller and lighter granules. For most uniform application, granules in turf fertilizers should be nearly the same size and weight. By evaluating each N carrier used in the fertilization program in addition to
the overall turfgrass quality and field performance from one year to the next, sports turf managers can make sure that they are getting the most from their granular N fertilizers. ■
Tom Samples is professor and extension turfgrass management specialist in the Plant Sciences Department at the University of Tennessee, Knoxville. John Sorochan is associate professor of turf- grass science in the Plant Sciences Department, and Adam Thoms is turfgrass research leader in the Plant Sciences Department in Knoxville. Editor’s note: References for this article are available on www.sportsturfonline.com.
14 SportsTurf | July 2011
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