chapter 2 abstract a field study was used to characterize...

CHAPTER 2

EFFECT OF MANAGEMENT FACTORS ON THE RATE

OF N RELEASE FROM SULFUR-COATED UREA

Abstract

Factors affecting the release of N from sulfur-coated urea (SCU)

must be known and considered when developing a fertilizer program. The

objective of this study was to determine how management decisions may

directly or indirectly affect release of SCU-N.

A field study was used to characterize N release from SCU of

different particle sizes. Five fine and four coarse SCU materials

from the Tennessee Valley Authority (TVA) were selected to represent a

range of 7-day dissolution rates. They were applied at a rate of

1.22 kg N/a to 324 cm2 plots. The weights of residual, undissolved

pellets were determined on whole plots sampled every 2 weeks for 12

weeks. From 16 to 90% of the applied SCU materials dissolved within two

weeks after application. In comparisons of fine and coarse SCU having

similar laboratory dissolution rates, the fine materials dissolved

significantly faster than the coarse materials.

The effect of traffic on pellet breakage was examined by applying

three SCU materials to an area subjected to mowing traffic two or three

times a week. Responses to traffic, as measured by weekly clipping

yields, color ratings and residual pellet counts were compared to

results from a non-traffic area. In the establishment year, yields

41

averaged over six occasions were 27% higher for ClL (Canadian Industries

Limited) SCU on the traffic area than on the non-traffic area. Color

and pellet counts did not reflect greater N availability due to breakage.

Response on plots fertilized with materials from TVA, SCU-ll and SCU-25

(11 and 25% 7-day dissolution rates) was not affected by traffic. No

treatments were differentially affected by traffic in the second year.

To examine the effect of thatch and mowing height on pellet break-

age, SCU was applied to turf with thatch depths of 2.1 and 2.8 cm and

with mowing heights of 1.9 and 3.8 cm. Uniform pressure was applied to

the SCU with a modified penetrometer and undamaged pellets were collected

and weighed. Pellet breakage decreased by 4 to 6% as thatch depth

increased; however, mowing height had no effect. Pellet breakage was

significantly greater on bare soil than on turf areas.

The effect of previous fertilization and soil pH on dissolution of

SCU were examined by incubating SCU in nine soils for eight weeks. A

fumigated soil was compared to soils previously fertilized for four

years with SCU or a soluble N source. All three soils were adjusted to

pH 6.0, 7.0 or 8.0. After incubation, residual pellets were weighed.

Release of SCU ranged from 6 to 10% faster in soil previously fertilized

with SCU than in a fumigated soil. Soil pH had no effect on dissolution

of SCU.

Introduction

Slow-release fertilizers often have an important role in the

management of high quality turfgrass. Coating a soluble N source,

typically urea, with an impermeable material is one approach used to

produce slow-release fertilizers. Sulfur-coated urea (SCU), a product

of this approach, is becoming very popular in the turfgrass industry.

Sulfur-coated urea is less expensive than other slow-release fertiliers,

and has been shown to be an effective N source for turfgrass fertil-

ization (Davies. 1976; Hummel and Waddington. 1981; Volk and Horn. 1975;

Waddington and Duich, 1976; Woolhouse, 1973,1974).

Sulfur-coated urea is produced by spraying atomized molten sulfur

on preheated urea granules or prills (Rindt et al., 1968; Scheib and

McClellan, 1976). A sealant such as wax or a mixture of polyethylene

and heavy-weight oil is often applied to seal defects in the sulfur

coating. Nitrogen is released by degradation of the sealant or sulfur

coating (Jarrell and Boersma, 1980). Release rates are characterized by

a 7-day dissolution rate, which indicates the percent of urea that goes

into solution when SCU is immersed in water at 38°C for 7 days. An

alternative method of predicting the potential field response to seufertilization was proposed by Jarrell et al. (1979). The authors

postulated that three classes of seu granules exist: Class I granules

have unobstructed holes through the coating and release urea as soon as

they are wetted; Class II granules have holes in the coating that are

filled with a sealant and release urea after the sealant is broken down;

42

Class III granules have sulfur coatings with no holes in them and

release urea as soon as the sulfur coating is penetrated. This charac-

terization has not yet been correlated to response in the field.

The release rate of seu is strongly influenced by the manufac-

turing process. Different release rates may be obtained by varying the

coating weight (thickness) or coating method (Lunt, 1967). In field

studies, Waddington and Turner (1980) reported that turfgrass response

to seu applications varied with coating weight and coating method, and

that the 7-day dissolution rates were not always reliable in predicting

response in the field. The inclusion of a wax sealant or microbicide

in the production of seu has been shown to decrease the release rate of

seU-N compared to materials with sulfur-only coats (Rindt et a1., 1968).

Various environmental conditions may influence release rates of

seu. Release rates were found to increase with increasing temperatures

(Allen et al., 1971; Oertli, 1973; Prasad, 1976). These results suggest

that materials with thicker coatings may produce better results in

warmer climates while thinner coatings may be more appropriate where

cooler temperatures prevail. Dawson and Akratanakul (1973) and Prasad

(1976) found that N release from seu increased with increasing soil

water potential. A moisture variable probably explains why Allen et al.

(1971) and Prasad (1976) found that the release of N from seu was faster

when mixed into the soil, than when surface applied. In flooded soils,

however, release of seu was shown to be much slower than rates obtained

in aerated soils (Giordano and Mortvedt, 1970). The authors suggested

43

44

that the activity of aerobic, wax-degrading microorganisms was inhibited

by the anaerobic environment. Liming the soil was reported to increase

the rate of N release from seu (Giordano and Mortvedt, 1970; Hashimoto

and Mullins, 1979); however, this effect was small. In solution culture,

release of seu was not influenced by pH differences in the range in

which crop plants are grown (Oertli, 1973). The importance of these

factors on the release of seu was thoroughly discussed by Jarrell and

Boersma (1979).

Turfgrass management and management decisions may affect release of

SCU-N directly or indirectly by their influence on the turfgrass environ-

ment. Sulfur-coated urea materials are commercially available to turf-

grass managers in different particle sizes. Advantages to using a smaller

particle size include: better coverage due to more particles per unit

area; better size for blending; and reduced mower damage and pick up.

However, as particle size decreases, the surface area per unit weight of

fertilizer to be coated increases. If sulfur is applied at the same rate

per weight of fertilizer, decreasing the particle size will decrease the

coating thickness. A material with a thinner coating will tend to have

a faster release rate (Lunt, 1967; Allen et al., 1971; Allen and Mays,

1971). Mowing may influence release of seu. Tractor and mower traffic

were found to cause pellet breakage, and consequently, fertilizer burn on

bentgrass fairway turf fertilized with high rates (2.9 kg N/a) of 'Gold-N'

seu and a TVA experimental seu (D. V. Waddington, unpublished data). As

thatch accumulates, or mowing height is increased, a decrease in pellet

breakage from mowing traffic could be expected. Mowing is also an

important factor when seu is applied to close-cut turf. due to pellet

pick up and removal (Gowans and Johnson, 1973). Woolhouse (1974)

reported that 17 to 21% of applied seu was removed from turf mowed at

5 mm. Fertilization practices may also influence release of seu.

Release of SeU-N has been shown to increase on soil previously fertil-

ized with seu (S. E. Allen, personal communication). These data suggest

that microorganisms that selectively utilize the wax sealant or sulfur

coating as an energy source. are increasing their populations in response

to an abundance of substrate provided by seu applications. It is impor-

tant that the effect of management factors on release of seu be known,

so that they may be considered when developing a fertilizer program

using seu. The objective of this study was to determine the effect of

particle size, thatch, traffic, mowing height, soil pH, and fertilization

history on the release of N from seu.

Materials and Methods

Experiments 1, 2 and 3 were conducted at the Joseph Valentine

Turfgrass Research Center, University Park, PA. Experiment 4 was con-

ducted in a laboratory. The soil used in all four experiments was a

Hagerstown silt loam (fine, mixed, mesic Typic Hapludalf).

45

46

Experiment 1: Effect of Particle Size

The turf used in this study was a three-year-old stand of 'Pennfine'

perennial ryegrass (Lolium perenne L.). The dissolution characteristics

of ten SCU materials were determined. Five materials were fine-particle

experimental SCU fertilizers (94% passing 8 mesh and retained on 12 mesh

screen) made with curtain-granulated urea by the Tennessee Valley

Authority (TVA). Four coarse-particle SCU materials (9S% passing 6 mesh

and retained on 10 mesh screen) were made with pan-granulated urea by

TVA. The tenth material was a sulfur-coated urea prill (85% passing 8

mesh and retained on 12 mesh screen) manufactured by Canadian Industries

Limited (CIL). Descriptions of fine (f) and coarse (c) materials and

designations used in this paper to indicate a material are as follows:

SCU-10f: 35-0-0; 10% dissolution rate; average pellet weight of

3.9 mg.

SCU-11c: 36-0-0; 11% dissolution rate; average pellet weight of

14.8 mg.

SCU-1Sf: 36-0-0; 15% dissolution rate; average pellet weight of

4.7 mg.


14.7 mg.

SCU-2Sf: 36-0-0; 25% dissolution rate; average pellet weight of

5.0 mg.


11.1 mg.

seU-32f: 37-0-0; 32% dissolution rate; average pellet weight of

5.0 mg.

SeU-30c: 36-0-0; 30% dissolution rate; average pellet weight of

12.1 mg.

eIL-30p: 32-0-0; 30% dissolution rate; average pellet weight of

6.2 mg.

Seu-42f: 38-0-0; 42% dissolution rate; average pellet weight of

4.7 mg.

All materials were applied on 17 June 1981 at a rate of 1.22 kg

N/are(a) (2.5 lb NI1000 ft2) to each plot.

Plot size was 324 cm2, which represented the area within a 20.3 em

diameter ring. The small plot size made it feasible to sample the entire

plot, insuring that a representative sample was taken. A randomized

complete block design with three replications was used. Enough plots

were placed in the field so that six samplings could be made. After seu

application, plots were sampled every 2 weeks for 12 weeks. Whole plots

were removed as plugs of turf and soil, and the residual undissolved

pellets were collected and weighed.

Data were subjected to an analysis of variance, and means were

compared using the Waller-Duncan Least Significant Difference Test with

k=lOO (Waller and Duncan, 1969).

47

Experiments 2 and 3: Effect of Traffic,

Thatch and Mowing Height

The turf used in experiment 2 was Merion Kentucky bluegrass (Poa

pratensis L.). A nested classification of a randomized complete block

design, with three replications was used. Plot size was 4.57 by 1.52 m.

An area adjacent to the stand described in Chapter 1 was used for a

48

traffic treatment. •The areas were seeded at the same time but the

location used for traffic had a thinner turf stand.

Six N sources were applied to the adjacent areas at a rate of 2.45

kg N/a (5 lb N/lOOO ft2),split into equal spring and fall applications.

These N sources included TVA seU-ll (36-0-0), TVA seU-25 (37-0-0), elL

seU-30 (32-0-0), ureaform (38-0-0), lBDU (31-0-0) and ammonium nitrate

(33.5-0-0). After initial fall fertilization in 1978 and during the

1979 and 1980 growing seasons, one of the two areas was subjected to

supplemental traffic two or three times a week using a Toro Professional

70-inch mower equipped with l6x6.50-8 tubeless terra tires. Assuming

an operator weight of 180 lb (81.6 kg) and a mower weight of 450 lb

(204.2 kg), a static pressure of 14.4 psi (1.01 kg/cm2) was applied.

The mowers were not engaged, and the traffic pattern was varied with each

date to distribute traffic throughout the plot area. The traffic on

any given day was only what would have been necessary to mow the turf

with that mower. In September and October, 1980, the traffic was inten-

sified by riding the mower over the area once a week, making sure the

entire surface was covered by wheel traffic each time. The adjacent

area was not subjected to these traffic treatments.

49

Weekly clipping yields and color ratings and pellet recovery were

the response criteria used to determine if fertilizer treatments were

differentially affected by traffic. Clippings were collected from 2.06

m2, which represented one pass across the length of the plot with a

20-inch reel mower.

To assess turfgrass quality, visual color ratings were made for

each clipping date. Ratings were made using a scale of 0 to 5, using

half units, with 5.0 indicating darkest green and 0 indicating yellow

or straw colored turf. Values of 3.0 and above were assigned to plots

having acceptable color. Data for yield and color were analyzed to

determine if a location (traffic) x N source interaction occurred. The

assumption was that pellet breakage would increase N availability, which

would be reflected in color and yields.

Plots that had received seu applications were sampled prior to

spring, summer and fall fertilizations, and in November of 1978, 1979 and

1980. Samples were used to determine the amount of residual, undissolved

SCU. Six 10.2 cm diameter plugs were removed from each plot, representing

a sampling area of 490 cm2• Residual pellets were recovered and weighed.

Experiment 3 was conducted to determine if thatch accumulation or

mowing height influenced SCU breakage. Two thatch depths were used in

this experiment. The uncompressed thatch depths ranged from 2.70 to 2.84

cm ('Nugget' Kentucky bluegrass) for the thick depth, and 2.07 to 2.14 cm

(Pa K-194 Kentucky bluegrass) for the thin depth. These plots were

maintained at l,~ cm and 3.8 cm mowing heights. Soil that was devoid

of turf for two years, but having similar physical properties as the

soil under turf, was included for comparison.

The seu materials used included TVA SeU-ll, TVA SeU-25 and elL seu-

30. These materials were placed at a rate of 2.45 kg N/a on the turf or

soil surface within the confines of a 5.1 cm diameter cylinder. A layer

of cheesecloth was placed between the surface and the seu to aid in

pellet recovery.

Pressure was applied at 224 x 10~ dyne/cm2 (32.5 psi) to the seu

with a penetrometer modified with a 5.1 cm diameter foot. After pressure

was applied, the undamaged pellets were collected and weighed. Means

were compared using a Fisher LSD test (0.05) (Steel and Torrie, 1960).

Experiment 4: Effect of Previous

Fertilization and Soil pH

Three soil treatments were selected for this laboratory study.

Two soils were sampled from the same experimental plot area; one soil

had been fertilized with seu for four years before sampling, the other

had been fertilized over the same time with a water soluble N source com-

posed of ammoniated phosphate and ammonium sulfate. The third soil was

fumigated with methyl bromide. The three soils were adjusted to pH 6.0,

7.0 and 8.0 using HCl or Ca(OH)2. The water content of the three soils

was then adjusted to 20% H20 (wt/wt), approximately field capacity.

50

Three materials were selected for this study: TVA-26w (37-0-0,

26% dissolution rate, 2% wax sealant), TVA-26 (35-0-0, 26% dissolution

rate, no sealant), and TVA-2l (33-0-0, 21% dissolution rate, 2% wax

sealant with coal-tar microbicide). The seu materials were mixed in 250

g soil, at a rate of 500 mg N. The soil and seu mixtures were covered

and incubated at 23°e for 8 weeks. At the end of this period, the intact

pellets were removed from the soil and weighed.

Results and Discussion


Release characteristics varied among the seu materials used in

this study (Table 9). The slowest releasing material initially, was

SeU-llc, with only 16% of the seu releasing within 2 weeks after fertil-

ization. Dissolution rates of the other treatments ranged from 39 to

90% of the applied seu releasing within 2 weeks after fertilization.

These high percentages of readily available N account for the quick

initial yield and color responses observed in the field from seu fertili-

zation (Hummel and Waddington, 1981; Waddington and Turner, 1980).

The fastest releasing materials were SCU-42f and ClL-30p, with 90%

and 82%, respectively, of the applied SCU releasing 2 weeks after appli-

cation. Despite having similar 7-day dissolution rates, the release of

seU-N was faster for the fine materials than the coarse materials (Table

9, Figure 14). This result occurred for all comparisons of similar

51

Three materials were selected for this study: TVA-26w (37-0-0,

26% dissolution rate, 2% wax sealant), TVA-26 (35-0-0, 26% dissolution

rate, no sealant), and TVA-2l (33-0-0, 21% dissolution rate, 2% wax

sealant with coal-tar microbicide). The SeD materials were mixed in 250

g soil, at a rate of 500 mg N. The soil and SeD mixtures were covered

and incubated at 23°e for 8 weeks. At the end of this period, the intact

pellets were removed from the soil and weighed.

Results and Discussion


Release characteristics varied among the SeD materials used in

this study (Table 9). The slowest releasing material initially, was

SeD-lIe, with only 16% of the seu releasing within 2 weeks after fertil-

ization. Dissolution rates of the other treatments ranged from 39 to

90% of the applied seu releasing within 2 weeks after fertilization.

These high percentages of readily available N account for the quick

initial yield and color responses observed in the field from seu fertili-

zation (Hummel and Waddington, 1981; Waddington and Turner, 1980).

The fastest releasing materials were seU-42f and eIL-30p, with 90%

and 82%, respectively, of the applied seu releasing 2 weeks after appli-

cation. Despite having similar 7-day dissolution rates, the release of

seU-N was faster for the fine materials than the coarse materials (Table

9, Figure 14). This result occurred for all comparisons of similar

51

Table 9. Residual undissolved pellets recovered from turf grassfertilized with sulfur-coated urea on 17 June 1981.

Sampling Date (1981)Treatment 2 4 6 8 10 12

Percentage of applied seu recovered

SeU-lOf 62 bc~ 45 b 37 c 21 d 14 d 14 e

SeU-llc 84 a 81 a 62 a 59 a 64 a 64 a

SeU-15f 52 c 40 b 23 d Be 8 de 7 f

SeU-16c 67 b 47 b 58 a 42 b 42 b 49 b

SeU-25f 42 d 18 c 12 e 4 f 3 ef 0 f

SeU-25c 61 bc 44 b 34 c 35 c 34 c 22 d

SeU-32f 25 e 8 cd 5 ef 0 f 0 f 0 f

SeU-30c 61 bc 43 b 49 b 44 b 42 b 30 c

eIL-30p 18 ef 13 cd 8 ef 4 f 4 ef 4 f

SeU-42f 10 f 4 d 0 f 0 f 0 f 0 f

aMeans followed by the same letter are not significantly different(k=lOO).

52

53

0 t:

I• 0• ~oM• O~- I ;;~ ell• al U•() .... • bOoM

!" CO ellr-lIt) &0 ~ p..N N () - • t: p..• al ellON •I I • U

rt)rt)• '"' '"':) :) • U>• al al0 0 I I • Z p..~•en en :):) • 0 ~• al t1l00 •• - .c

f/)f/)• J- ~ ct)~ ~ al~ ~ t: IS~ 0 oM

~ (.) ~!toft; - al

~ ..J N ~~. C\I oM t:

0- ct) al'"'0- al al

~ r-l~U~

oM oMN ~-O- '"'iii • t1l ~. • a::• • p..t1l

I• •

l&J• • .• • - -0-0• . .0 .... t: al• . .• -. .. lL t1l '"'- - • al~ • al :>U 'to- • ~Q ~ I • • ~ 0• • t1l cJ~ • •• •

'"' OJI I I - ! CO ...•:) :) en t:

0 :; U_ ~ 0 ...-lU ~ CD &0 - ~ oM ellen C/) :; ~ ~oM

~ft; ~ U) I&J ::l ...I I r-l al

= ;:):):; I&J o ~• :; ct) t1l• 00 :; ~ Ul IS.... ~ oM.: en(/) ,:; ~ "Cl~:; ~ U

~ .: ~ U)

~ ~ 0.: "Cl~ ~ al.: - UoM- ~ t\J alr-l~ p..~p..W tIl

0 0 0 0 -<t...-l

0 It) 0 It) al

'"'::lbe

Q3~3I\O:>3~ n::>s % oM~

dissolution rates. The data in Table 9 show that the rate of release

of the Sell-10f was similar to the Sell-25c over the 12-week period.

Thus, if a fine-particle sellwere to be used for turfgrass fertiliza-

tion, a material with a 7-day dissolution rate of 10% would be expected

to produce turf of similar vigor and quality as that produced by a

coarse-particle Sellwith a dissolution rate of 25%. Turfgrass fertil-

ization with fine materials with dissolution rates greater than 15%

would require more frequent applications at lower rates of N. When

elL sellof two particle sizes and similar dissolution rates were com-

pared, however, turfgrass response was similar (Hummel and Waddington,

1981).

Highest seu pellet recovery 12 weeks after fertilization occurred

with Sell-lIe and SeU-16c, with 64% and 49%, respectively, of the applied

Sellmaterial recovered. These results indicate that the materials may

release N too slowly to produce turfgrass of acceptable quality; however,

the accumulation of residual Selland its release in later years may

improve turfgrass response to these materials over time.

54

Experiments 2 and 3: Effect of Traffic,

Thatch and Mowing Height

The reason for using a nested classification of a randomized complete

block design was to determine if fertilizer treatments were differentially

affected by traffic. Following the initial fall fertilization, pellet

breakage was not indicated by any of the criteria. In the following

summer, significant (0.05) traffic by N source interactions for yield

were observed for only six of the clipping dates (Table 10). None

occurred for color ratings or residual pellets.

The treatments least affected by traffic were SCU-ll, SCU-25,

ureaform, and IBDU. There was a tendency for lower yields on the traffic

area with these treatments, but this was probably due to a density

difference present since the area was established, rather than a differ-

ential effect of compaction on N release.

The treatments most affected by traffic were CIL-30 and AN.

Ammonium nitrate plots in the traffic area produced yields averaging

28% less than the traffic area over the six weeks in 1979 when a signifi-

cant fertilizer by traffic interaction occurred. On CIL-30 plots, yields

for the six dates averaged 27% higher on the traffic area than on the

non-traffic area. These differences, however, occurred several weeks

after application, when very little ClL-30 is left in the soil to be

broken (Experiment 1). If dissolution of CIL-30 were increased due to

pellet breakage, the turfgrass response to increased N availability

would be expected to resemble that from AN. Higher yields on the traffic

area than on the non-traffic area with ClL-30 fertilization suggested

that there was pellet breakage; however, on the traffic area, yields

with CIL-30 were considerably greater than with AN. One would expect

responses from broken SCU to approach or equal that of AN, but not to

55

00....-I ..;t C""l \0 a C""l I'- Lf'\ C""l NN I'- 0\

'"Cl ....... Lf'\ ..;t ..;t Lf'\ C""lLf'\ C""l..;t I'- \0 C""l C""lQ) 0\,...,...::luu0

a I'- ....-I Lf'\ N C""l \0 0\ I'- a ....-IC""l O\N0 ....... I'- Lf'\ 0\ 0\ 00 ....-I C""l..;t C""l C""l Lf'\..;t

'M 00 ....-I ....-1....-1-I-lUC\l,...Q)-I-la ""''M ""' ..;t 00

0\ N '-' 01'- Lf'\ Lf'\ N N 0....-1 Lf'\ I'- 00 0\Q) I'- ....... Lf'\ ..;t I'- I'- I'- ....-I NN 1'-'\0 \0 ..;tU 0\ I'- '"Cl ....-I,... ....-I ....-I::l '-' Q)0 'M(J) Q) ,>,

-I-lZ C\l -I-l

'"Cl .c~ a 0000....-1 'M C""l00 ..;t I'- 00 N Lf'\N ....-10\ a 0\u a .......Q) ..;t C""l 00 I'- 00 N ....-1....-1 \0 C""l 0\ I'-

'M 'M I'- ~ ....-I.... p...... p.. .cC\l 'M (J),...

....-I Q)-I-l U ,...~aQ)

~C""l 0Lf'\ C""l0\ 0\ a ....-I 0\ Lf'\ I'- \0 ....-I....... ..;tN I'- ..;t I'- 00 N ....-I ..;tN ....-I I'-I'- ....-I

(J)

Q)-I-lC\l

'"Cl

0\I'- \00\ N 0C""l 00 ..;t C""l ..;t 0\ Lf'\ 00\0 0\ \0....-I ....... C""l C""l Lf'\ \0 \0 00 ....-I N NN 0\0

\0 ....-I,...0....(J)

'"Cl....-IQ)'M U U U U U U>, -I-l '''; 'M '0-1 '0-1 .0-1 '0-1

a .... .... .... .... .... ....." Q) .... u .... u .... u .... u .... u .... u.c S C\l '0-1 C\l '0-1 C\l '0-1 C\l 'M ell 'M C\l '0-100 ." '"'

.... '"' .... ,... .... '"' 4-< '"' 4-< ,... 4-<'0-1 C\l E-< 4-< E-< 4-< E-< 4-< E-< 4-< E-< 4-< E-< 4-<Q) Q) C\l ctl C\l C1j ctl ctl~ ,... 0 ,... ~ '"' 0 ,... 0 ,... 0 ,... o '"'I E-< Z E-< E-< ZE-< ZE-< ZE-< ZE-<

.c(J)Q),...~

a Q)....-I U ....-I Lf'\ a

'"' ....-I N C""lQ) ::l I I I B....-I 0 B ~ ...J

..0 Cf.l U H ~ P::lC\l Cf.l Cf.l U ~ H

E-< Z

56

57

exceed it. This unexplained variability, plus the fact that the inter-

actions occurred much later than expected, indicated that the interactions

may have been artifact of variability. The selection of a more uniform

area, or the use of a design that could account for the variability

between areas, may have resulted in more meaningful data.

In 1980, few significant interactions occurred. When interactions

were present, no treatment appeared to be clearly affected by traffic.

Even under severe traffic, there was no significant effect on seu break-

age. There may have been greater pellet breakage in 1979 than in 1980

because there was not enough thatch accumulated in the establishment

year to cushion the seu from the mower, while in 1980 there was. These

results prompted a more thorough examination of the effect of thatch on

pellet breakage.

Thatch was found to have a significant effect on pellet breakage

(Table 11); pellet breakage decreasing with increasing thatch depth.

Pellet breakage was 60%, 64% and 83% higher on bare soil than on

the 2.1 em thatch depth, for SeU-ll, SCU-25 and eIL-30, respectively.

Breakage on the 2.1 em thatch depth was significantly greater than on

the 2.8 em depth; however, these differences were not very large. These

data show that seu pellet breakage should decrease as a thatch layer

develops during the establishment year, but additional thatch accumulation

will not decrease breakage very much. lhese results may explain why a

treatment traffic interaction occurred only in the establishment year of

the traffic study.

Table 11. Effect of thatch and mowing height on the percentage of applied SCU recovered from turf.

Mowing Height (cm)

Thatch Depth (cm)

N Source

1.9

3.8

2.07-2.14 2.70-2.84

Bare Soil

% SCU Recovered

SCU-llc

39

39 ns

38

41

16

SCU-25c

28

25 ns

23

29

8

CIL-30p

35

32 ns

29

35

5

Two treatments were significantly different (0.05). Bare soil results were significantly lower

than all other treatments.

00

59

Mowing height had no significant effect on seu pellet breakage;

however, there was a tendency for more breakage at the 1.9 cm mowing

height, especially for the elL seu (Table 11). It is possible, though,

that the presence of the thatch layer at both mowing heights negated the

effect of mowing height. If this were true, then mowing height may

influence pellet breakage on recently established turfgrass stands or

other stands having little thatch accumulation.

Experiment 3: Effect of Previous

Fertilization and Soil pH

Release of N from seu was slightly faster on soils previously

fertilized with seu than on soils fertilized with soluble N (Table 12);

however, these differences were not significant. Microorganisms have

some influence on the release of seu because release was significantly

slower on the fumigated soil, for all three seu materials. The impor-

tance of this role is still questionable, however, because 59 to 71% of

the seu placed in the fumigated soil released in 8 weeks. These results

indicate that chemical and physical processes involved in release of

seu are at least as important as biological processes, as has been

suggested in the past (Hummel and Waddington, 1981).

Coating a seu material with a coal tar microbicide (TVA-21) proved

to be an ineffective means of slowing the release of seu, because pellet

recoveries were as high as the TVA-26w, that had no microbicide (Table 12).

Ul llJ llJ

C C C:::>uUl

0 ..... \D ....."';l ,..., N ,...,~ CXl

:::C-C- o ..... .n ........ ...... ,..., N ,...,'. ~ ...... Ul'- 0 ..Il:8 Ul ~~ill 0 :- \D ,..., \DDC ,..., N ,...,l"l \0 CC4.JC ""~ ~U 4.J"" .....~ C\lc.. .....~ ~~ 0 C\l4.J tIl N .n .n

C CC ~......~ ~ COc.. 0 c

Ul ~...... C~ " ~0 ~ C\l \0 0- .....Ul 4.J e "'" N -::t

C\l ClJ" tlC ""C ......l"l E :::>=' uC t.>.. Ul0...... "4.J ~l"l ~N ......... c........ c c..

...... 0 C\l4.J ~ Z"" 4.J .....~ r:l <l.I 0'- N ......

...... ~ ~ ~ N "'" N

(/) ...... ...... ,..., N ,...,=' 0 ......~ Ul 4.J 0

...... "" r.r::> E <l.I<l.I 0 t.>.."" ""c.. '- (/)

=''- " 00 <l.I ...... :::> 0 0- 0"" :> u "'" ...... ","" ~4.J ill <l.I Ul L'"'\

U :> "" c<l.I 0 0....... U C..... <l.I

u..; ""ClUl...J

r'J <l.I...... u 3 """" \0 \0 ...... <l.I

<l.I =' N N N .c0 I I I en

•.0 [f' ~ ~ ~ .....re ~ > > t.>..

f-o Z f-< f-< C\l

60

Allen et al. (1971) also found that the addition of a microbicide

had little effect on release of SeD in the field.

Soil pH, ranging from 6 to 8, had no effect on the dissolution of

SeD (Table 12), supporting the work of Oert1i (1973).

Conclusions

Several factors were found to influence the rate at which N is

released from seD. It is important that these factors are known and

taken into account when developing a fertilizer program based on SeD.

In comparisons of fine and coarse SeD having similar laboratory

dissolution rates, fine-particle seD released N more quickly than the

coarse-particle SeD. Pellet recovery for the fine materials with low

7-day dissolution rates was similar to the coarse materials with

dissolution rates 15% higher. Field studies are necessary to measure

turfgrass response to these experimental fine-particle SeD materials,

so that recommendations for their use may be made.

Results suggested that traffic may have caused breakage of elL

seU-30 during the establishment year. Pellet breakage was insignificant

in the second year, probably due to the accumulation of a thatch layer.

With the equipment used to apply traffic in this study, little breakage

of seu can be expected. The effect of traffic on seu breakage using

heavier equipment needs investigation. Pellet breakage decreased as

thatch depth increased; however, changes in pellet breakage were small

with a thatch thickness increase from 2.1 to 2.8 em.

61

Differences in pellet breakage at 1.9 cm and 3.8 cm cutting heights

were insignificant on thatchy turf. If no thatch had been present, it

is probable that mowing height would have had a significant effect on

breakage.

Release of seU-N was slightly faster on soil previously fertilized

with seu compared to fumigated soil, suggesting that microorganisms may

not be totally ignored as a factor responsible for the release of SeU-N.

The extent of their importance in this process is questionable. Soil

pH, when within the range of 6 to 8, had no effect on release of seu.

62

chapter 2 abstract a field study was used to characterize...

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