CHAPTER 1 EVALUATION OF SULFUR-COATED UREA FOR TURFGRASS FERTILIZATION Abstract The acceptance of sulfur-coated urea (SCU) as a fertilizer in the turfgrass industry necessitates a firm basis on which to make recommen- dations for its use. Three SCU materials were evaluated at different rates and timing of application for maintenance fertilization of Merion Kentucky bluegrass (Poa pratensis L.). Two were SCU materials from the Tennessee Valley Authority (TVA): SCU-ll and SCU-25, having 11% and 25% 7-day dissolution rates. The third. CIL-3D, was a S-coated urea prill from Canadian Industries Limited (CIL). Ammonium nitrate (AN). ureaform (UF). and lBDU were also evaluated for comparison to SCU. Response to fertilization was measured by weekly determinations of clipping yields and color. Nitrogen recovery in the clippings and residual SCU pellets in the turf stand were also determined. Data were collected for three growing seasons. The most uniform turfgrass response was produced by SCU-25 and CIL-3D when applied at a rate of 2.45 kg N/are(a)/yr. split into two appli- cations. When SCU-25 and ClL-30 were applied at a rate of 2.45 kg N/a in single fall applications. there was insufficient carry-over of residual N to maintain dark color throughout the growing season. Under the condi- tions in which this test was conducted. release of N from SeU-ll tended to be too slow to maintain good color. Only the single spring application
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CHAPTER 1
EVALUATION OF SULFUR-COATED UREA
FOR TURFGRASS FERTILIZATION
Abstract
The acceptance of sulfur-coated urea (SCU) as a fertilizer in the
turfgrass industry necessitates a firm basis on which to make recommen-
dations for its use. Three SCU materials were evaluated at different
rates and timing of application for maintenance fertilization of Merion
Kentucky bluegrass (Poa pratensis L.). Two were SCU materials from the
Tennessee Valley Authority (TVA): SCU-ll and SCU-25, having 11% and 25%
7-day dissolution rates. The third. CIL-3D, was a S-coated urea prill
from Canadian Industries Limited (CIL). Ammonium nitrate (AN). ureaform
(UF). and lBDU were also evaluated for comparison to SCU. Response to
fertilization was measured by weekly determinations of clipping yields
and color. Nitrogen recovery in the clippings and residual SCU pellets
in the turf stand were also determined. Data were collected for three
growing seasons.
The most uniform turfgrass response was produced by SCU-25 and
CIL-3D when applied at a rate of 2.45 kg N/are(a)/yr. split into two appli-
cations. When SCU-25 and ClL-30 were applied at a rate of 2.45 kg N/a in
single fall applications. there was insufficient carry-over of residual
N to maintain dark color throughout the growing season. Under the condi-
tions in which this test was conducted. release of N from SeU-ll tended
to be too slow to maintain good color. Only the single spring application
of seU-ll at 2.45 kg N/a maintained good color throughout the summer.
Fertilization rates of 1.47 kg N/a/yr did not produce acceptable quality
turf. Pellet recovery was inversely related to N recovery in plant tissue.
Pellet recoveries ranged from 3 to 9% for elL-3D, 20 to 40% for SeU-2S,
and 47 to 62% for SeU-II, when sampled two months after application.
Average N recoveries for three years were highest for ammonium nitrate and
ClL-3D with 49 to 59% and 50 to 56%, respectively, of the applied N
recovered in plant tissue. Nitrogen recoveries of 42 to S2% and 25 to 37%
were obtained for SeU-25 and SeU-II, respectively. Recoveries averaged
22% for UF and 46% for IBDU. Response to IBDU compared favorably to SCU-
25, while response to UF was less than from any other 2.45/2 treatment.
Introduction
Sulfur-coated urea (SCU) is a slow-release N source that has been
gaining acceptance in the turfgrass industry. It is manufactured by
spraying molten, atomized S on preheated urea granules or prills in a con-
tinuous flow process (Shirley and Meline, 1975). A sealant such as wax,
or a mixture of polyethylene and heavy-weight oil is often applied to seal
micropores in the S coating. A conditioner (diatomaceous earth) is added
to reduce the cohesiveness of the sealant and to make the surface hydro-
philic. The final product contains 32 to 38% N, 13 to 20% S, 2 to 3%
sealant and about 2% conditioner on a wt/wt basis (Blouin et al., 1971).
Early evaluations found seu to be an effective slow-release N source
for the fertilization of bermudagrass, Cynodon dactylon (Allen et al.,
1971; Mays and Terman, 1969a; Rindt et al., 1968) and tall fescue,
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Festuca arundinacea Schreb. (Mays and Terman, 1969b). These studies,
however, were conducted to evaluate seu as a potential slow-release N
source for forage fertilization, and have only limited applicability to
seu fertilization of turfgrass.
One of the first seu materials made commercially available for turf-
grass fertilization was 'Gold-N', a sulfur-coated urea prill made by
Imperial Chemical Industries, Ltd. Woolhouse (l973, 1974) found that when
split into spring and summer applications, 'Gold-N' produced high quality
turf similar to that produced from multiple applications of ammonium
sulfate. Volk and Horn (1975) found that seu made by the Tennessee Valley
Authority (TVA) and having a 9% 7-day dissolution rate gave more favorable
results than IBDU, ureaform, and activated sewage sludge. In studies on
'Pennpar' creeping bentgrass (Agrostis palustris), Waddington and Duich
(1976) found the response to SeU-2l (21% 7-day dissolution rate) to be
intermediate to IBDU and ureaform (Uramite). More recent work has shown
that field response to seu materials can vary, depending on coating thick-
ness and coating method (Waddington and Turner, 1980). When compared to
response from several other slow-release and soluble N sources, turfgrass
response to spring and fall applications of seu has been superior (Hummel
and Waddington, 1981). Other agronomic aspects of seu have been reviewed
by Davies (1976).
While the agronomic potential of seu as a turfgrass fertilizer is well
documented, data are lacking in regards to the most efficient rates and
timings of application for different seu materials. A firm basis on which
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to make recommendations for SCU use is needed. The objective of this
study was to characterize the dissolution of three SCU materials in the
field, and to evaluate these materials at different rates and timings
for maintenance fertilization of Kentucky bluegrass turf.
Materials and Methods
This test was initiated on 27 September 1978 at the Joseph Valentine
Turfgrass Research Center, University Park, PA, and was concluded on
14 September 1981. The turf was 'Merion' Kentucky bluegrass (Poa pratensis
L.), which was seeded on 18 August 1978. The soil was a Hagerstown silt
loam (fine, mixed, mesic Typic Hapludalf) that had an initial pH of 6.8,
84 ppm of Bray no. 1 extractable P, 0.24 meq/lOOg of exchangeable K, and
a CEC of 9.4 meq/lOOg in the surface 5 cm. A randomized complete block
design with three replications was used. Plot size was 1.3 by 4.6 m.
Irrigation was applied only when signs of wilt occurred.
Two SCU materials from the Tennessee Valley Authority (TVA) were
designated SCU-ll (36-0-0, 11% 7-day dissolution rate) and SCU-25 (37-0-0,
25% 7-day dissolution rate). For both SCU-ll and SCU-25, 95% passed
through a 6 mesh screen and was retained ana 12 mesh screen. They were
applied at a rate of 2.45 kg N/are(a)/yr (5 lb N/lOOO ft2) in one (spring,
fall), two (spring + fall) and three (spring + summer + fall) applications.
They were also applied at a rate of 1.47 kg N/a/yr (3 lb N/lOOO ft2) in
two (spring + fall) applications. Another SCU material, manufactured by
Canadian Industries Limited and designated CIL-30 (32-0-0, 30% 7-day
dissolution rate, 85% passing a 8 mesh and retained on a 12 mesh screen)
was applied at a rate of 2.45 kg N/a/yr in one (spring, fall) and two
(spring + fall) applications. Three other N sources were included for
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