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,

2

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

3

4

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

comparison. Isobutylidene diurea (IBDU, 31-0-0, 27.9% WIN, 0.7-2.5 rom)

and granular ureaform (UF, 38-0-0, 27% WIN) were applied at a rate of

2.45 kg N/a/yr in two (spring + fall) applications. Ammonium nitrate

(AN, 33.5-0-0) was applied at a rate of 2.45kg N/a/yr in two (spring +

fall) and four applications, and was also applied at a rate of 1.47 kg

N/a/yr in two (spring + fall) applications. Treatment designations for

rate-timing combinations are listed in Table 1.

Table 1. Designation of rates and timing of fertilization.

5

Designation

2.45 F

2.45 S

2.45/2

2.45/3

2.45/4

1.47/2

Treatment

2.45 kg N/a/yr in a single fall application

2.45 kg N/a/yr in a single spring application

2.45 kg N/a/yr split into equal spring and fallapplications

2.45 kg N/a/yr split into equal spring, summerand fall applications

2.45 kg N/a/yr split into four equal applications

1.47 kg N/a/yr split into equal spring and fallapplications

Response to fertilization was measured by weekly determinations of

fresh-weight yields and color, and N recovery. Clippings were collected

from 2.06 m2, representing one pass along the length of the plot with a

reel mower. Cutting height was maintained at about 3 cm and all clippings

were removed. After fresh-weight yields were obtained, the clippings

were forced-air dried at 60°C and combined over dates for four growth

periods within each fertilization year. Dry weights were obtained, then

clippings were analyzed for total N using a micro-Kje1dahl procedure

(Isaac and Johnson, 1976). Two plugs (81 cm2) were removed from each plot

at the end of each fertilization year (prior to September fertilization)

to determine N recovery in the roots and plant tissue remaining after

mowing. Soil was washed from the roots, and the remaining tissue was

dried and analyzed for total N using the method cited above.

To assess turf quality, visual color ratings were made for each

clipping date. Color was rated on a scale of zero to five, using one-

half units, with five indicating darkest green and zero indicating yellow

or straw-colored appearance. Color rated less than 3.0 was considered

unacceptable for good quality turf.

Plots that had received SCU applications were sampled in November

of each fertilization year, and then prior to each spring, summer and fall

fertilization to determine residual SCU pellets. Six plugs (81 cm2) were

sampled from each plot and were broken apart to collect the residual,

undissolved pellets. These intact pellets were weighed, and the percentage

of applied SCU that was recovered was calculated.

Changes in soil pH were recorded at the end of each fertilization

year. At the conclusion of the study, soil pH was determined at depths of

o to 0.6 cm and 0.6 to 5 cm.

6

Clippings from the last growth period in 1981 were analyzed for P,

K, Ca, Mg, and Mn with a RF Plasma Emission Spectrometer (Dahlquist and

Knoll, 1978). Tissue S was determined with a Leco high-frequency induc-

tion furnace with an automatic S titrator.

Clipping yields, color ratings, N recovery, residual pellets, soil

pH, and tissue composition data were subjected to an analysis of variance,

and means were compared using the Waller-Duncan L.S.D. test with k=lOO

(Waller and Duncan, 1969).

Temperature and precipitation data for the three fertilization years

are shown in Figure 1. Data represent accumulated rainfall and averages

of daily mean temperature for each week.

Results and Discussion

Clipping Yields and Color

Results of fresh-weight clipping yields are shown in Table 12 of

the Appendix. Color ratings for each clipping date are shown in Table 13

of the Appendix. Means were compared using the Waller-Duncan Least

Significant Difference Test (k=lOO) and the letters following the clipping

weight or color rating allow for comparisons of treatments within a

column (one clipping date). Means followed by the same letter are not

significantly different.

Turfgrass response and overall quality varied with N source, rate

of N, and timing of application. Acceptable color in the fall and spring

and high early spring yields were characteristic of turf fertilized with the

7

8

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seU-ll 2.45 F treatment (Figure 2). Acceptable color, however, was

maintained only through May and poor color was present for the remainder

of the summer. Splitting this rate into two applications improved the

response to SeU-ll in the summer months; however, color still tended

to be unacceptable « 3.0 rating) throughout most of the year (Table 2).

Although the release of N from SeU-ll tended to be too slow to produce

acceptable color, a single spring application of 2.45 kg N/a provided

enough available N to produce acceptable color throughout the summer.

The performance of the 2.45 S treatment was superior to other SeU-ll

treatments. Although turfgrass quality tended to be poor in the seU-ll

treated plots, there was a trend for increased yields and darker color

over the three years, especially in 1981. The extremely dry fall in 1980

(Figure 1) resulted in low turfgrass response to fall fertilization.

The carry-over of N from fall 1980, along with improved growing condi-

tions in 1981, could account for improved response to all treatments.

Yields and color ratings from seU-ll were often significantly lower

than SeU-25 and e1L-30 (Table 3), especially for the 2.45/2 treatments.

Initial yield and color responses to fertilization with e1L-30 2.45/2

were often greater than SeU-25 2.45/2 (Figure 3); accounting for the

differences noted in Table 3. Overall, the occurrences of acceptable

color produced by SeU-25 and e1L-30 were similar (Table 2), and both

materials were superior to SeU-ll over the entire season.

The initial response to the high rates of N from single applications

of ClL-30 included excessively high yields and very dark color (Figure 4).

9

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16

Because of quick dissolution of CIL-30, the 2.45/2 produced a more uniform

and desirable response throughout the year than the single applications.

High yields and dark color were produced in the fall and spring on

turf fertilized with the SCU-25 2.45 F treatment (Figure 5). Like the

SCU-ll and CIL-30, this response lasted only through May of the following

year, and unacceptable color remained until the next fall application.

This characteristic of the 2.45 F treatments is undesirable because

summer is the time when turf utilization is often at its maximum, and

when turf is expected to have both aesthetic and resilient qualities.

The single spring application of SCU-25 produced good color throughout

the summer; however, the yields produced from this high rate of N would

necessitate more frequent mowing in most management schemes. Higher

rates of available N have also been shown to deplete carbohydrate

reserves making the turf more susceptible to stress (Schmidt and Blaser,

1967; Watschke and Waddington, 1974, 1975; Zanoni et al., 1969). In

areas where heat and drought stress frequently occur, application of

high rates of N should be avoided, regardless of the N source.

The SCU-25 2.45/2 produced a uniform response to fertilization with

acceptable color produced through most of the year (Table 2). Occur-

rences of acceptable color were similar for the SCU-25 2.45 Sand 2.45/2

treatments. Although there were few significant color differences

between these two treatments following spring fertilization, density

differences were noticed in 1981 when the 2.45 S treatment appeared less

dense.

17

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18

The uniformity of N release as reflected in yield and color is well

illustrated when SeU-25 2.45/2 is compared to AN 2.45/4 (Figure 6). The

AN 2.45/4 was selected as a treatment in this test because several light

applications of a soluble N source would be expected to produce a uniform

response to which other treatments could be compared. However, on Merion

Kentucky bluegrass, the 0.61 kg N/a was not sufficient N to maintain

dark color for long durations. As a result, large fluctuations in color

occurred.

Yield and color data for the SeD-25 2.45/2 ~nd SeU-25 2.45/3 are

compared in Figure 7. The higher rate of N applied with the 2.45/2

treatments produced slightly higher yields and darker color than the

2.45/3 after fertilization. Both treatments produced acceptable color a

similar number of times after the first year, except in late summer when

acceptable color was produced more often on 2.45/3 treated turf. Although

turf color is improved by a midsummer application, this improvement may

not be justified by the cost and inconvenience of a third application.

Low yields and poor color were characteristic of the 1.47/2 treat-

ments (Figure 8). Yields increased and color improved following appli-

cation of AN and SeD-25, but this response was short in duration.

Although response to SeD-ll fertilization was much less than AN or SeD-2S,

all 1.47/2 treatments failed to produce acceptable color most of the

year (Table 2).

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22

Turfgrass response to SCU-25 2.45/2 was compared to UF 2.45/2, IBDU

2.45/2, and AN 2.45/2. Yields and color ratings produced by UF were

consistently lower than SCU-25 (Figure 9). The poor quality turf pro­

duced by UF throughout the entire test is reflected by the data in Table

2. Response to IBDU 2.45/2 fertilization included the delayed response

that is characteristic of IBDU (Hummel and Waddington, 1981; Moberg et

al., 1970; Waddington et al., 1977; Wilkinson, 1977). This response

resulted in IBDU usually producing higher yields and darker color than

SCU-25 in early spring and late summer (Figure 10, Table 2). Except in

1980 when the occurrence of unacceptable color was greater for IBDU,

both SCU-25 and IBDU maintained acceptable color. Since dissolution and

hydrolysis are necessary for N release from IBDU, the unusually dry

summer in 1980 (Figure 1) could account for the poor performance during

that year. The AN 2.45/2 produced excessively high yields and dark color

after application (Figure 11). Acceptable color was then maintained for

six to eight weeks after fertilization. Because of the more uniform

release of N from SCU-25, the occurrence of acceptable color was more

frequent than with AN (Table 2).

Pellet Recovery

Yield and color data were used to characterize release of N from SCU

over time. The release characteristics of SCU were also evaluated by

recovering intact SCU pellets. Weighing the residual pellets made it

possible to quantitatively determine the amount of SCU released within

23

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Z10 0C\II

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Zj:a::IIII Il..... 0 •

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24

25

N......111-:r.N

111N

I:JUenI-l0~III

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26

each growth period (Table 4). The first sampling was made two months

after application, and it revealed that eIL-30 had the fastest dissolu-

tion rate of the three SeD materials, with 91 to 97% of the SeD from

single applications being released in this time (Figure 12). This fast

dissolution explains why high yields and dark color are typical responses

to elL seD fertilization. The SeD-II was the slowest of the three

materials with only 38 to 53% of the applied material releasing in two

months. The SeD-25 was intermediate with 60 to 80% of the applied

material releasing in two months.

Twelve months after 2.45 F and 2.45 S applications, 28% of the applied

SeD-II was found unreleased in the turf (Figure 12) compared to 4% for

SeD-25 and 1% for eIL-30. The slow dissolution of SeD-II 2.45 F resulted

in an accumulation of seD over three years (Figure 13) that represented

26% of the applied material. There was no evidence, however, that these

residual pellets were releasing in later years because the amount of

SeD-II released in 1981 did not increase over the amounts released in

the previous two years (Table 4) and the residual SeD continued to

increase over the 3-year period (Figure 13). The residual SeD-II pellets

must therefore be very resistant to breakdown and would be expected to

persist in the soil for several years. Accumulation of SCD-25 and eIL-30

was much less than SeD-II.

In the fall of 1980, the amount of seD-ll released from the 2.45 F

treatment was 37% lower than in the fall 1979. This apparent effect of

"'dc::III

CIlC1I4.1III~4.1

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27

28

ol.Jttt'tl

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29

30

moisture on release of seD was also noted by Dawson and Akratanakul (1973),

and Prasad (1976), and it suggests that under heavily irrigated turf-

grass, release of SeD-II may be much quicker than was observed in this

study.

Split applications of the SeD materials resulted in a more uniform

release of SeD over the growth periods. This was especially true for

the 2.45/3 treatments.

Release of seD did not correlate well with dry weight production

within each growth period (SeD-II, r=O.14; seD-25, r=O.17; elL-30,

r=0.26). The release of seD within a growth period following fertil-

ization does not necessarily mean that all the N released is utilized

by the plant. There was often enough carry-over of N in the soil to

produce high dry-weight yields for two growth periods after fertiliza-

tion (Table 15, Appendix). This carry-over explains why residual yield

and color responses to SeD-25 and elL-30 were similar despite the quicker

dissolutions of the elL material.

Nitrogen Recovery

Nitrogen recovery in the clippings was expressed as a percentage of

the N applied for each growth period (Table 16, Appendix) and was calcu-

lated from the dry weight (Table 15, Appendix) and tissue N concentration

data (Table 17, Appendix). Annual N recovery data (Table 5) were expressed

as percentages of the N applied for each fertilization year. Because an

unfertilized check treatment was not included, N recovery was not adjusted

for the contribution of soil N.

Table 5. Effect of fertilizer treatment on annual N recovery inplant tissue.

31

Treatment 1979

Nitrogen RecoveryaFertilization Year

1980 1981

SCU-ll-------%-------

2.45 F 29 fgb 28 e 39 k

2.45 S 26 fg 31 de 54 d-f

2.45/2 27 fg 30 de 43 i-k

2.45/3 29 fg 25 ef 41 jk

1. 47/2 22 g 22 f 31 1

SCU-25

2.45 F 53 b-d 42 ab 47 g-j

2.45 S 49 cd 43 ab 64 ab

2.45/2 43 de 42 ab 53 d-g

2.45/3 34 ef 41 bc 52 d-g

1.47/2 46 d 35 cd 48 f-i

CIL-30

2.45 F 63 ab 48 a 44 h-k

2.45 S 66 a 44 ab 59 b-d

2.45/2 53 b-d 44 ab 53 d-g

Ureaform

2.45/2 23 g 14 g 28 1

IBDU

2.45/2 50 cd 38 bc 50 e-h

Ammonium nitrate

2.45/2 61 ab 48 a 69 a

1.47/2 57 a-c 39 bc 62 bc

2.45/4 53 b-d 38 bc 57 c-e

MEA.~S 44 36 50aExpressed as a percentage of the N applied per year.

bMeans followed by the same letter are not significantly different(k=100)

Highest N recoveries were obtained from the ClL-30 and AN treat-

ments; however, in 1980, N recoveries for SCU-25 treatments were not

significantly different from these two materials. Nitrogen recoveries

tended to be lower in 1980 than in 1979 and 1981. The dry summer in

1980 resulted in lower dry weight production. and consequently. low N

recovery.

Low N recoveries were characteristic of SCU-ll and ureaform.

Nitrogen recovery results reported by Hummel and Waddington (1981) and

Moberg et al. (1970) showed residual N effects from low recovery

materials. With continued use, performance of these materials may be

expected to increase (Waddington et al., 1976).

Nitrogen recovery from plant tops and roots (Table 6) are expressed

as a percentage of applied N for each fertilization year. These values

were calculated from dry weight and tissue concentration of N. found

in Table 17 of the Appendix. The total amount of the N recovered from

plant tops (after mowing) and roots represented a small percentage of

the total N applied. No clear trends were present except N recovery

was significantly higher for the 1.47/2 treatments of SeU-ll. SeU-25.

and AN. The higher rate of N applied with the other treatments may have

stimulated shoot growth at the expense of root growth. Root growth

would therefore be lower and N recovery less. relative to the amount of

N applied. High N levels have been shown to suppress root growth and

carbohydrate reserves (Schmidt and Blaser. 1967; Zanoni et al .• 1969).

32

~ Z"'Ot1l Q) ~ "'0 bO ~ bO..c: bOQ) bO "'O~ ..c:Q) Q) ,... I

oj 1:, () I I I I I I I ..c: I I I...-l bOQ) .0 .0 .c <11.0 () "'O~ Q).o Q) ..-4 bO .0"'0 ~

ell ::-,... 0 0\ \0 I' C"'l 0 0) I' ...-l -:t C"'l lI"l-:t 00 0\ 0 -:too lI"lQ) ()

CIl ~<11 1'C"'l...-lC"'lll"l C"'l -:t I' -:t ...-l C"'l 0\ N C"'l 00 ...-lll"l ...-l

<-J ,... lI"l 1'\0 \O-:t lI"l \0 lI"l lI"l lI"l lI"lll"lll"l N -:t \OlI"l lI"l00,... .......

CIl"'0 ,...r:: ojoj "'0 CIl Q) .......

Q) <-J >'0CIl ::- Q) () ..c: ~ bO OM 0p.. ...-l...-l () t1l.o .0"'0 bO Q) Q) Q) ~ .... ..c: OM Q)...-l0 O...-l Q) "<-J CIl Q) 0 C"'l C"'l C"'l C"'l I' C"'l 00 C"'l C"'l C"'l I' ,...~'-' CIl p.. . ..c::'-'

OM -:t -:t \0 0\ ...... -:to 0\ 0 lI"l 0...-l0 <-JCIl "'0 ::::J N C"'l N N ...-l ...-l ...-l <-J<-J r:: U ,... t::r:: ::::J u) 0 Q)t1l t1l ~ ,...

...-l >. Q)p.. ,... Q)~

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p:: =' CO t1l ...-l>. Ul bO iN! ..c: .... Q) "'0 ~ bO~ Q) Q) ~ () Q) '-' <-JH r:: Ul r:: OM I I .... or; I I I I I I .0 I I I I t::Q) Q) OM OM ..c: ~ bO..c: OM .0 t1l () Q)"'O ell ell t1l ....., () t1l ell .0 H t1l::- bOE-t p.. t1l ()

0 0 p.. 0 0 C"'l I' 0 C"'l 0 0 C"'l 0 ...... C"'l0 I"'- 0 C"'l I"'- C"'l Q) OM() ,... ~ oM >.~Q) <-J ell...-l N I"'- C"'l ...-l If') l"'- N \0 N C"'l ...-l\0 0 ...-l \0 0\ N 0\ "M,... OM Q) () C"'l C"'l C"'l C"'l N -:t If') -:t -:t -:t If') If') If') N -:t If') If') -:t H t::

Z.....:l'-' Q) bOZ p.. oM

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EO <-J 0 t1l H<-J Q) 0 t1lt1l ...-l H ZQ) ...-l Ul .0 HH Q) <-J"'O ~ Q) ~ Q) Q) Q) "'0 Q) Q) "0 ill OJ<-J p.. r:: t:: I () I () I I I ~ I I I I I ..c:: ....

ell ell "'0.0 .0 .0 t1l "'0 .0 .0 .0 t1l ~ Q) .0 .0 () .0 t1l .0 .... ....H ...-l ...-l Q)

Q) t1l 0... Ul 0\ C"'l ...... C"'l ...... 0\ -:t ...-l ...-l 0 If') 00 ...-l N 0 ...... ...... N '""' ......N =' p.. C

OM "'0 C ...-l N N N N ...... N N N C"'l ...-l ...-IN N N NC"'l N~...... OM .... Q)

OM CIl '-'" or..... Q) Cll "./lH H ....Q) C OJ~ "0 11

t:: u w~ t1l I-<

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(oJ .... E "M -<

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..0 ~ ~-:t~~-:T ~ -:T ~-:T~-:T .....l -:T~~ t1l-:T Cl~

o~l~~~ Ul

U U ...... Q) c:l ° Q) 'J:Q) U'l N N N N --i U'l N N N N --i U N N N l-< N H.~J eN ...... ('J I-< ~

~ " ~ ......... c...0 gl >< Q)

~ t::\ w:.tE-t <, '"::.0

33

Nitrogen recovery has been used extensively in N source evaluation

studies to determine fertilizer efficiency, that is, the amount of N

applied that is removed by the plant. Unfortunately, the amount of

residual N remaining in the soil is often neglected. As a result, N

recovery is often highest for water-soluble or quick-releasing N sources

(Hummel and Waddington, 1981; Moberg et al., 1970; Slater, 1966), where

all of the N is available to the plant within a short time after appli-

cation. In this study, N recovery from SCU treatments was found to be

inversely related to pellet recovery (r=-0.79). If the residual N in

the soil were measured and taken into account, N recovery may actually

be higher for the slow-release materials. Waddington et al. (1976)

found N levels highest in soils fertilized with Milorganite and UF for

seven years. Waddington and Turner (1980) recovered 0 to 13% of applied

seu 2~ years after the last application. The nature of N release from

seu, and pellet size make it possible to reclaim intact pellets, and

estimate residual N. However, this is at best an estimate because the

N content of residual pellets may be as much as 20% lower (average 10%

lower) than the N content of applied particles (Waddington and Turner,

1980). When residual N was taken into account, N recovery from SCU-Il

and SCU-25 was comparable, and in some cases higher than AN (Table 6).

Elemental Composition of Plant Tissue and Soil pH

Tissue concentration of P varied among the treatments (Table 7).

Plant tissue P was inversely related to the dry weight for the sampled

growth period (r=-0.8l). Turf fertilized with materials having low N

34

35

bO........bO;:1.

'U 'U'U..0 I'U I I(1j (1j U ..0 III..-jN-:t\O..-j0\00 ............00

U'O 'U'OI 1..0 I ICIl III III CIl CIlO\C"'lOLl)C"'l00000\0000

'UU

LI)......

'U

o......

. . .000

0\lf"\00000

000

..0..0CIl I1l IIINNOLl)LI)\o000

o

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Q)

ICIl

NoN

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o

......\0

o

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. . .000

Ill..o CIlC"'l\00LI)-:tLI)000

Ql 'HI ~ ICIl Ql I1l

\0 -:tC"'l\oLI)\O000

..0..olll..o000 ......-:tLl)-:t000

O~(/)NC"'l -...ILI)LI)LI)......-:t-:t-:tHUNNN

(/)NC"'lN........ -... -...Ll)LI)LI)......

-:t-:t-:t-:tN N N..-j

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.. .00000

OOO\LI)-:too000..-j0

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U'U..o'O..ou'U\oNLI)C"'l..-j-:t-:t-:t-:t-:t. . . . .00000

U'H~'H U1 I I I ICIl ..0 III U CIl

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LI)~NIll)

:::>-:tU(/)N

. . . . .00000

0\ LI)LI)\0 00NNNNN

..0 ..0Ill..o..o..olllO\OLI) ......O\LI)-:t-:t-:t-:t.....00000

'U Q)'UU'U'U'UNC"'l..-j..-jO-:t-:t-:t-:t-:t.....00000

'O~~~I I I 1..0CIl'O..oUCIl

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..-j~(/)NC"'lN..-j ........ILI)LI)LI)LI) ......:::>-:t-:t-:t-:t-:tU(/)NNNN..-j

~t::Q)

S~IIIQ)~HQ)

~..0(1jH

availability in a given sampling period, such as the 2.45 F or 1.47/2

treatments, had high tissue concentrations of P. Treatments with high

N availability such as lBDU, AN, and the 2.45 S treatments, had high

dry-weight yields that diluted the concentration of tissue P.

Potassium, Ca, and Mg concentrations were not significantly affected

by the treatments. Sulfur concentrations were significantly higher on

seu treated plots, especially with the ClL-30 treatments. The higher

S content of ClL-30 (22% vs 17 and 16% for SeU-l1 and SCU-25,respec-

tively), as well as the quicker release rat~made more S available for

oxidation and plant uptake. These data show that use of SCU may be

advantageous where S is limiting.

Manganese concentrations were directly related to S concentrations

in plant tissue (r=0.78). Sulfur effects on Mn availability are well

documented (Caldwell et al., 1969; Hassan and Olson, 1966; Tisdale and

Bertramson,1949). The acid media created by oxidation of S would favor

reduction of Mn4+ to Mn2+; however, Tisdale and Bertramson suggested

that the increased availability of Mn2+ in soils is due primarily to the

reducing effect of the S itself, not due to an increase in acidity.

Since there was no significant effect of SCU on soil pH (Table 8), their

explanation seems to be logical for the increased Mn concentrations in

plant tissue.

Fertilizer treatment had little effect on soil pH; however, pH did

decrease with time for all treatments (Table 8). The greatest decrease

in pH was in the surface 0.6 cm of soil. Although seu has a large

36

Table 8. Effect of fertilizer treatment on soil pH.

37

TreatmentInitial 1979

0-5 cm

Year1980

pH

19810-0.6 cm 0.6-5 cm

SCU-ll2.45 F2.45 S2.45/22.45/31.47/2SCU-252.45 F2.45 S2.45/22.45/31.47/2CIL-30

2.45 F2.45 S2.45/2Ureaforrn2.45/2IBDU2.45/2

Ammonium nitrate2.45/21.47/22.45/4

6.77

6.806.876.77

6.80

6.876.836.876.77

6.73

6.806.806.70

6.80

6.87

6.77

6.836.77

6.536.506.476.506.50

6.476.676.536.336.30

6.236.576.47

6.47

6.76

6.576.606.67

6.33 aba6.37 ab6.33 ab6.43 ab6.17 b

6.30 ab6.33 ab6.37 ab6.40 ab6.57 a

6.30 ab6.40 ab

6.30 ab

6.27 ab

6.40 ab

6.27 ab6.37 ab6.27 ab

5.60 ab5.42 a-c5.72 a

5.53 ab5.82 a

5.45 a-c5.68 a

5.43 a-c5.48 a-c5.67 a

5.10 c

5.55 ab5.18 bc

5.68 a

5.60 ab

5.75 a

5.62 a

5.75 a

6.285.926.156.406.17

6.286.026.176.325.90

6.076.326.25

6.35

6.40

6.406.286.32

~eans followed by the same letter are not significantly different.

potential acidity because of the elemental S, pH values were not signifi-

cantly lower than those caused by other N sources, except for the 0 to

0.6 cm depth in 1981 for two ClL treatments.

Conclusions

Turfgrass response varied with N source, rate and timing of appli-

cation. Pellet recoveries 12 months after application varied from 30 to

38% for SCU-ll, compared to 4% for SCU-25 and 1% for ClL-30. The slow

release of the SCU-ll resulted in an accumulation of pellets over three

years that represented 26% of the applied material. Turfgrass response

to the SCU-ll treatments tended to be poor under the conditions of this

study. Only the 2.45 S produced high yields and dark color throughout

the summer months. Yields were higher and color was darker on SCU-ll

plots in 1981; however, this improved performance was apparently due to

better growing weather in 1981 and not to the release of accumulated

pellets.

The low ClL-30 pellet recoveries two months after application

indicated a very fast dissolution rate for this material in the field.

Because of the quick release of ClL-30, high yields and dark color

following application were characteristic. Only the 2.45/2 treatment

produced acceptable color uniformly throughout the year. Although the

release of SCU-25 was slower than CIL-30, turfgrass response to these

materials was similar. The 2.45 F and 2.45 S treatments of SCU-25 and

38

e1L-30 produced excessively high yields after application, but neither

provided sufficient residual N to maintain acceptable color throughout

the year.

The most uniform turfgrass response produced was to SeU-25 2.45/2

and SeU-25 2.45/3; and the differences in response between these treat-

ments may not justify the third application. The 1.47/2 treatments of

SeU-II, SeU-25, and AN did not supply enough N to produce acceptable

turf color on this stand of Merion Kentucky bluegrass. The delayed

response to lBDU fertilization resulted in darkest color being produced

in late summer and early spring. Despite their differences in release

characteristics, IBDU and SeU-25 were similar in the percentage of weeks

that turf color was acceptable.

Fertilization of turfgrass with seu increased Sand Mn concentra-

tions in plant tissue. Tissue P decreased as dry weights of clipping

increased.

39