25

PAPER II. THE GROWTH RESPONSE Of KENTUCKY BLUEGRASS TURF TO UREASE

INHIBITORS AND CATIONIC MATERIALS APPLIED IN COMBINATION

WITH UREA

26

The Growth Response of Kentucky Bluegrass Turf to Urease Inhibitors and

Cationic Materials Applied in Combination with Urea

2 Y» K. Joo and N. E. Christians

Contribution from the Department of Horticulture, Iowa State

University. Published as Journal Paper No. J- of the Iowa

Agriculture and Home Economics Experiment Station, Ames. Project 2231.

Graduate Research Assistant and Professor, respectively.

Department of Horticulture, Iowa State University. Ames, Iowa 50011.

27

ABSTRACT

Urea is a major source of nitrogen (N) fertilizer for the turf

industry. Fertilization with urea in both liquid and dry forms involves

the risk of considerable N loss to the a~osphere as gaseous ammonia

(~). Amongthe methods that have been proposed to reduce this N loss

are the application of urea with urease inhibitors and the combinations

of urea with cationic materials. The obj ective of the studies reported

here was to evaluate the urease inhibitors phenylphosphorodiamidate

(PPD). !!-(.E.-butyl) thiophosphoric triamide (NBPT), and ammonium

thiosulfate (ATS) and to evaluate cationic materials potassium (K+) and

magnesium (Mg++) as f.ertilizer amendments for increasing urea-N

efficiency by measuring the effect of these compoundson growth response

following application of urea to Kentucky bluegrass (poa pratensis L.)

turf. The first experiment conducted in growth chambers was a screening

trial to evaluate PPDand MgC12in combination with four rates of N (0,

49, 98, 148 kg ha-1) at two temperatures (20/13, 27/18oC). The PPDwas

included at 1 and 2%and Mg++at 25%.of the weight of N. The 25%Mg++

treatment was the most effective in reducing foliar burn. This effect

was more evident in the low temperature than in the high temperature

treatment. The average fresh weight of clippings over a three-week

period in pots treated with PPDincreased at both temperature treatments.

The treatments for the two-year field test included liquid urea

applied monthly in June through September in 1985 and 1986 at 49 kg N

ha-1 (1 Ib N/1000 ft2) with the urease inhibitors PPD (1. 2. 3%of the

28

weight of applied N), NBPT (0.5. 1, 2%). and ATS (5, 15. 25%), andcationic materials K+ (5. 15.25%) and Mg++(5, 15, 25%) at three rateseach. Th . M ++ d + d .e catJ.ons.g an K re uced folJ.arburn and increased turfquality during mid- and late summer of 1985 at the 5% rate. Clippingyield was not affected by urease inhibitors or by the cations. In 1986.under milder climatic conditions. the urease inhibitors PPD and NBPTtreatments significantly increased clipping yield. The cationicmaterials KCl and MgCl2 reduced foliar burn and increased visual turfquality in mid-summer. Plots treated with ATS increased clipping yieldat the 15% rate; however. PPD and NBPT were much more effective than theATS treatment. Clipping yield varied with month of application, and theeffect of PPD. and NBPT on percentage yield increase was greatest in heatstress perio.ds. The fresh weight of clippings averaged over a four-weekperiod in plots treated with 2% PPD increased 30.0% in June, 35.5% inJuly, 13.9% in August, and 8.3% in September as compared with the controlplots. The average increase over four months was 12.0%, 21.7%, and 6.0%with the 1. 2, and 3% PPD treatments. respectively. The fresh weight ofclippings averaged over a four-week period in plots treated with 2% NBPTincreased 21.1% in June, 27.0% in July, 16.6% in August. and 9.9% inSeptember over the control. The average increase over four months was

14.7%. 12.4%. and 18.4% with the 0.5. 1. and 2% NBPT treatments.respectively. Clipping yield response varied among the weeks followingapplication. Yield increase showed a maximum in the first week at the 2%rate of PPD and decreased in weeks two through four. Yield increasereached a maximum in the second and third weeks with 0.5% treatment of

29

NBPT. and increased into the fourth week at the 1 and 2% rates.Responses to urea-N lasted longer at the higher levels of NBPT. Thestudies reported here did not measure the quantity of NH3 volatilizeddirectly; however, the positive effects of the urease inhibitors PPD andNBPT on growth response indicate that a reduction of N loss and anincrease in N-use efficiency are possible when these materials arecombined with liquid urea applications on Kentucky bluegrass turf. Theurease inhibitors PPD and NBPT deserve further consideration asfertilizer amendments for the turfgrass indust~.

Additional index words: Urease inhibitors,Phenylphosphorodiamidate. !!-(!!.-butyl)thiophosphoric triamide, Ammoniumthiosulfate, Potassium chloride, Magnesium chloride, Ammonia

volatilization, Turfgrass.Fertilization.

30

INTRODUCTION

Urea is a major source of nitrogen (N) fertilizer for the turf

industry because of its low cost. relatively low salt index. and its

compatibility in tank-mixed solutions with many of the pesticides used on

lawns. Because of its versatility. liquid fertilization is rapidly

becoming a popular method of applying urea to turfgrasses. The

disadvantages of liquid fertilization of urea include potential foliar

burn and relatively short residual response (Wesely. 1983). Many

researchers have reported that the surface application of urea. in both

solid and liquid forms. also involves the risk of considerable N loss to

the atmosphere as gaseous ammonia. and field studies have shown urea to

be less efficient than other N sources when surface-applied on grass sad

(Volk. 1959; Gasser. 1964; Tomlinson. 1970; Spangenberg et al •• 1986).

Laboratory and greenhouse studies have been conducted to investigate

NH3 volatilization from urea and the factors which affect it. Among

these factors are urease activity. soil pH. temperature. water content.

rainfall. NE3 sorbing capacity of the soil. and rate and method of urea

application (Ernst and Massey. 1960; Gasser. 1964; Overrein and Moe.

1967; Tomlinson. 1970; Hargrove and Kissel. 1979; Mulvaney and Bremner,

1981; Bouwmeester et al •• 1985; O'Toole et al., 1985; Ferguson and

Kissel, 1986).

Torello and Wehner (1983) demonstrated that urease activity within a

turf thatch layer and urease activity associated with turfgrass tissue

were 18 to 30 times higher than fram underlying soil. Their findings

31

suggest that when urea is applied to turf, the high urease levels in

thatch could result in greater NH3 volatilization, regardless of the soiltype, than is normally observed in other types of soil-plant systems.

One approach to minimizing the problems encountered in use of ureais to find urease inhibitors that will retard urea hydrolysis whenapplied in combination with urea fertilizer. This approach has receivedconsiderable attention during the past 15 years, and numerous compoundshave been proposed or patented as soil urease inhibitor.s (Bremner andDouglas, 1971; Bremner and Mulvaney, 1978; Mulvaney and Bremner, 1981,Hauck. 1984: Martens and Bremner. 1984). Mos"tof these compounds are notvery effective and only phe~lphosphorodiamidate (PPD) has attractedsignificant attention. This compound was among a group ofphosphoroamides patented by Held et 81. (1976) for reducing gaseous lossof urea-N as ammonia when urea fertiliz.er is applied to soil. and recentwork (Martens and Bremner, 1984) indicated that it was more effectivethan compounds previously proposed for inhibition of urease activity insoil. However, subsequent work (Bremner and Chai, 1986: Chai andBremner. 1986) showed that .!!-(.!!-butyl)thiophosphoric triamide (NBPT) isconsiderably more effective than PPD for retarding urea hydrolysis insoU and merits serious consideration as a fertilizer amendment forretarding hydrolysis of urea fertilizer by soil urease. Ammoniumthiosulfate (ATS) used as a N and sulfur fertilizer has also beenproposed by Goos (1985) to have some urease inhibiting characteristics in

soU.Another concept concerning the reduction of NH3 loss from surface-

32

applied urea was presented by Fenn (Fenn et al•• 1981. 1982a. 1982b), who++ +. + ++studied the use of Ca, NH4 ' K , and Mg to reduce NH3 volatilization.

By their theory, all urea on the soil surface is converted to other formsof N within several days of application. The extremely rapid conversionof urea to ammonium carbonate is believed to be responsible .for the highammonia losses. However, cations in combination with urea are believedto reduce the rate at which urea decomposes. Rappaport and Axley (1984)also suggested that potassium (K+) from potassium chloride (Kel) can

potentially improve urea-N efficiency by reducing NH3 volatilization.In earlier field tests (1983 and 1984) ,the effectiveness of PPD and

MgC12 in increasing the efficiency of surface-applied urea on turf grassareas was evaluated. Positive results of potentially practical use onturf grass were observed with both materials (.100 and Christians, 1984;

Joo and Christians, 1986).The objectives of the studies reported here were to evaluate the

urease inhibitors phenylphosphorodiamidate (PPD). !!-(.!!.-butyl)thiophosphoric triamide (NBPT). and ammonium thiosulfate CATS) and toevaluate the cationic materials potassium (K+) and magnesium (Mg++) asfertilizer amendments for increasing urea-N efficiency by measuring theeffect of these compounds on growth response following their applicationwith urea to Kentucky bluegrass (poa pratensis L.) turf.

33

MATERIALS AND METHODS

A growth chamber test was conducted in 1984 and field tests wereconducted in 1985. and 1986 at the Iowa State University TurfgrassResearch area north of Ames. IA. The turf used in the experiments hadbeen established in 1981 on a 'Nicollet' Aquic Hapludoll fine loamy mixedmesic soil (pH 7.5. 2.3% organic matter) with a blend of 25% by weighteach of 'Parade'. 'Adelphi'. 'Glade'. and 'Rugby' Kentucky bluegrass (Poapratensis L.). The turf was irrigated as needed to prevent droughtstress throughout the study.

Pot Test in Growth ChambersThe pot test was conducted as a screening trial to evaluate the

effect of PPD and magnesium chloride (MgC12) on foliar burn and clippingyield of Kentucky bluegrass at four N rates in both high and lowtemperatures (Table 1).

The sod used in this test was obtained from the turf previouslymentioned. Grass was transplanted in 20 cm (8 inch) diameter plasticpots in October. 1983 and allowed to grow for at least three months inthe greenhouse before use. The soil used was prepared by mixing of equal

volume of top soil. peat. and perlite (pH 7.3). The grasses weremaintained in the greenhouse with a temperature regimes of 14 to 160C(night)/ 20 to 220C (day). Radiation levels were maintained during theday by sunlight and combination of metal halide and high-pressure sodiumlamps. The pots were mowed weekly at a 5 em (2 inch) height and

34

irrigated as needed. No additional N was supplied during growth in thegreenhouse. The pots selected for each replication were aclimated in thegrowth chambers for one week before treatment. One growth chamber wasset at a high temperature of 27/18oC (80/650F) and the other at a lowtemperature of 20/130C (68/55°). Illumination of growth chambers wereapprox. 250 microeinsteins m-2sec-1 with white fluorescent and tungstenlamps (General Electric, Inc.) with 12 hours photoperiod. All chemicaltreatments were applied with a spray-mist atomizer attached to an airpressure pump.

The experimental design was a split-split plot with two temperature++as main plots, four levels of N as subplots, and the two PPD and one Mg

rates as sub-sub plots (Table 1). The study was replicated five timesover a 15 week period. Temperature treatments were randomly assigned tothe growth chambers for each replication.

The degree of damage to turfgrass foliage was estimated visuallythree days after each application. The rating scale used ranged from 1to 9: 9 = no visual burn, and 1 = dead. Fresh clipping weights werecollected weekly for three weeks after each treatment at a 5 em (2 inch)

mowing height.

Field Test in 1985 and 1986The 1985 field test was designed in a randomized complete-block

arrangement with repeated treatments and measurements on the same plotareas in four replications. The treatments included liquid urea applied

1 2 ++ +at 49 kg N ha- (1 lb N/1000 ft ) with PPD, ATS, Mg , and K at three

35

rates each (Table 1). The 1986 field test was designed the same as the1985 test except for the addition of NBPT (Table 1). The 1986 test wasconducted on.an adjacent area to the 1985 study. The treatments wereapplied monthly in June through September in both years. Each plotmeasured 2.32 m2 (25 ft2). and each treatment was applied in the

-1 2equivalent of 500 liters H20 he (3 gallons H20/IOOO ft ) with a CO2backpack sprayer operated in four different directions to obtain uniform

application.The degree of damage to turfgrass foliage was estimated visually

three days after each application. The rating scale used ranged fran 1

to 9; 9 = no visual burn, and 1 = dead turf. Data on visual qualityratings based primarily on color. uniformity. and density were collectedon a weekly basis and rated on a scale o.f1 to 9: 9 = best quality, 6 =acceptable and 1 = poorest. Fresh weight of clippings were collectedweekly for five weeks after each treatment at a 5 em mowing height fromtwo strips through the center of the plots measuring 50 cm X 1.5 m (20inch X 5 ft) each. After data were collected, all plot areas were moweduniformly at the 5 em mowing height, and clippings were removed.

36

RESULTS AND DISCUSSION

The analysis of variance from the growth chamber test showed that

foliar burn was affected by N levels and chemical treatments of PPD and

MgCl2 (Table 2). Clipping yield was significantly affected by

temperature. N levels. and chemical treatments. ++The Mg at 25% of the

weight of N was the most effective treatment at reducing foliar burn.

This effect was more evident in the low temperature than the high

temperature treatment (Figure 1). The average fresh weight of clippings

over a three-week period in pots treated with PPD increased at boOth

temperature treatments (Figure 1). The results indicate that the PPD and++the Mg could have an effect on the N use efficiency of urea surface-

applied to Kentucky bluegrass turf.

In 1985. the environmental conditions recorded during the growing

season were not typical. The summer began with a very dry period which

retarded growth of Kentucky bluegrass. The effects of the treatments on

foliar burn and turf quality varied with chemical rates and time of

application (Table 3. Figure 2. Figure 3). + ++The K and Kg at the 5%

rate reduced foliar burn and increased turf quality during mid- and late

summer. although those effects were small. Clipping yield over a four-

month period varied with time of application. however, the treatment

effects were not significant (Table 3, Table 4). Those results are

likely due to the extended dry period in the summer of 1985 that began in

late May and extended through early August.

There was less stress on the grass in the 1986 study. The cation

37

treatments reduced burn and increased visual turf quality in July and

August (Table 3. Figure 2. Figure 3). Clipping yield increased on plots

treated with PPD and NBPT as compared with the control (N alone). but

there were no significant differences among the rates of PPD and NBPT.

Plots treated with the 15% rate of ATS had a clipping yield increase of

15.1%; however. ATS was much less effective than PPD and NBPT (Table 4).

The effects of PPD and NBPT on the percentage yield increase as

compare with the control were greatest in the heat stress period of July

(Table 4. Figure 4). This was likely due to increase NH3 volatilization

and decreased N efficiency during this high temperature period. The

fresh weight of clippings over a four-week period in plots treated with

2% PPD increased 30.0% in June. 35.5% in July. 13.9% in August. and 8.3%

in September as compared with the control plots. The average increase

over four months was 12.0% with the 1% PPD treatment. 21.7% with the 2%

PPD and 6.0% with the 3% PPD treatment (Figure 4). The 2% PPD rate was

the ~ost effective on the N use efficiency of surface-applied urea. but

3% PPD may not be practical as a fertilizer amendment for Kentucky

bluegrass turf.

The fresh weight of clipping yield over a four-week period in plots

treated with 2% NBPT increased 21.1% in June. 27.0% in July. 16.6% in

August, and 9.9% in September as compared with the control. The average

increase over four months was 14.7% with the 0.5% NBPT treatment. 12.4%

with the 1% NBPT and 18.4% with the 2% NBPT treatment (Figure 4). The

NBPT has a potential value for increasing N use efficiency of urea-N

applied as a liquid fertilizer. This effect may be possible at even

38

lower rates than 0.5% of the N weight (Table 3~ Figure 4).

Clipping yield response varied among the weeks following

application. Clipping yield increase (%) showed maximum in the first

week at the 2% rate of PPD and decreased in weeks 2 through 4. Yield

increase reached maximum in the second and third week with the 0.5%

treatment of NBPT and increased into the fourth week. at the 1 and 2%

rates. Responses to urea-N lasted longer at the higher levels of NBPT

(Figure 5).

39

CONCLUSIONS

The studies reported here did not measure the quantity of NIL

volatilized directly; however, the positive effects of the urease

inhibitors PPD and NBPT on growth response indicate a reduction of N loss

and an increase in N use efficiency are possible when these materials are

combined with liquid urea applications on Kentucky bluegrass turf. The

urease inhibitors PPD and NBPT deserve further consideration as a

fertilizer amendment for the turfgrass industry.

40

LITERA'IURE CITED

Bouwmeester. R. J. B •• P. L. G. Vlek. and J. H. Stumpe. 1985. Effect ofEnvironmental factors on ammonia volatilization fran a urea-fertilizedsoil. Soil Soc. Am. J. 49:376-381.

Bremner. J. H•• and H. S. Cbai. 1986. Evaluation of ~butylphosphorothioic triamide for retardation of urea hydrolysis in soil.Commun. Soil Sci. Plant Anal. 17:337-351.

Bremner. J. H., and L. A. Douglas. 1971. Inhibition of urease activityin soils. Soil BioI. Biochem. 3:297-307 •

Bremner, J. H., and R. L. Hulvaney.149-196. In R. G. Burns (ed.).London.

1978. Urease activity in soils.Soil Enzymes. Academic Press,

p.

Chai, H. S., and J. H. Bremner. 1986. Effects of phosphoroamides onammonia volatilization and nitrite accumulation in soils treated withurea. Agron. Abstr. 1986:176.

Ernst, J. W., and H. F. Massey. 1960. The effects of several factors onvolatilization of anmonia formed from urea in the soil. Soil Soc. Am.Proc. 24:87-90.

Fenn, L. B •• J. E. Matocha •.and E. Wu. 1982a. Soil cation exchangecapacity effects on ammonia loss from surface-applied urea in thepresence of soluble calcium. Soil Sci. Soc. Am. J. 46:78-81.

Fenn, L. B., J. E. Hathocha, and E. Wu. 1982b. Substitution of ammoniumand potassium for added calcium in reduction of ammonia loss fromsurface-applied urea. Soil Sci. Soc. Am. J. 46:771-776.

Fenn, L. B., R. H. Taylor, and J. E. Mathocha. 1981. Influence ofsoluble calcium and magnesium on ammonia losses from surface appliednitrogen fertilizers: General Theory. Soil Sci. Soc. Am. J. 45:777-781.

Ferguson, R. B., and D. E. Kissel. 1986. Effects of soil drying onammonia volatilization fran surface-applied urea. Soil Sci. Soc. Am.J. 50 :485-490.

Gasser, J. K. R. 1964. Urea as fertilizer. Soils and Fertilizers27: 175-180.

Goos, R. J. 1985. Identification of ammonium thiosulfate as anitrification and urease inhibitor. Soil Sci. Soc. Am. J. 49:232-235.

41

Hargrove. W. L•• and D. E. Kissel. 1979. Ammonia volatilization fromsurface applications of urea in the field and laboratory. Soil Sci.Soc. Am. J. 43:359-363.

Hauck. R. D. 1984. Technological approaches to improving the efficiencyof nitrogen fertilizer use by crop plants. p. 551-560. In R. D.Hauck (ed.). Nitrogen in Crop Production. American Society ofAgronomy. Madison. WI.

Held. POOl'S.Lang. E. Tradler. M. Klepe1, D. Drohne. H. J. Hartbrich, G.Rothe. H. Scheler. S. Grundmeier. and A. Trautmann. 1976. Agent forreducing the loss Qf plant-available nitrogen in cultivated soil.East German Patent No. 122.177. Chem. Abstr. 87:67315w.

Joo. Y. K •• and N. E. Christians. 1984. The reduction of ammoniavolatilization from turfgrass areas treated with surface-applied urea.Iowa turfgrass research report. Iowa State Univ. CooperativeExtention Service FG-450:42-45.

Joo. Y. K •• and N. E. Christian~+ 1986. The response of Kentuckybluegrass turf to PPD and Mg applied combination with urea. J.Fertil. Issues 3:30-33.

Martens, D. A•• and J. M. Bremner. 1984. Effectiveness ofphosphoroamides for retardation of urea hydrolysis in soils. SoilSci. Soc. Am. J. 48:302-305.

Mulvaney. R. L •• and J. M. Bremner. 1981. Control of ureatransformations in soils. p. 153-196. In E. A. Paul and J. M. Ladd(ed.). Soil Biochemistry. Vol. 5. Marcel Dekker. Inc.. New York.

O'Toole, P., M. A. Morgan. and S. J. McGarry. 1985.of urease activities in pasture and tillage soils.Plant Anal. 16:759-773.

A comparative studyCommun. Soil Sci.

Overrein. L. N •• and P. G. Moe. 1967.and ammonia volatilization in soil.61.

Factors affecting urea hydrolysisSoil Sci. Soc. Am. Proc. 31:57-

Rappaport. B. D•• and J. H. Axley. 1984. Potassium chloride forimproved urea fertilizer efficiency. Soil Sei. Soc. Am. J. 48:399-401.

Spangenberg. B. G •• T. W. Fermanian. and D. J. Wehner. 1986. Evaluationof liquid-applied nitrogen fertilizers on Kentucky bluegrass turf.Agron. J. 78:1002-1006.

Tomlinson. T. E. 1970. Urea: Agronanic applications. Proc. Fertil.Soc. 113:1-76.

42

Torello, W. A., and D. J. Wehner. 1983. Urease activity in a Kentuckybluegrass turf. Agron. J~ 75:654-656.

Volk, G. M. 1959. Volatile loss of ammoniafollowing surfaceapplication of urea to turf or bare soils. Agron. J. 51:746-749.

Wesely, R. W. 1983. Turfgrass response to foliar applied nitrogen.Ph.D. Thesis. Univ. of Nebraska, Lincoln. NE. 70 pp.

43

Table 1. Experimental treatment for pot and field tests

Treatments

Experiments

Pot test in

growth chamber

Field test

in 1985b

Field test

in 1986

N levels (kg ha-l)

0" 49" 98" 147

49

49

Chemical rates

PPD I" 2%8

Mg++ 25%

PPD I" 2" 3%ATS 5" 15" 25%

+K 5" 15" 25%

++Mg 5" 15" 25%

PPD 1" 2. 3%NBPT .5. 1. 2%

ATS 5" 15, 25%

K++ 5. 15. 25%

++Mg 5. 15. 25%

~ase on weight Of N (10% liquid urea).

bNBPr not available in 1985.

44

Table 2. The analysis variance of growth chamber test for foliar burnand clipping yield as affected by temperature. N level. ureaseinhibitor PPD and cation material MgC12

Source of variance dfMean squares

Burn rating clipping yie1da

Temperature 1Error A 4Nlev~s 3Temperature X N 3Error B 24chemicalsb 3Temperature X chemical 3N X Chemical 9Temperature X N X chemical 9Error C 96

3.45 6.44**1.84 0.21

18.61** 0.82**0.44 0.45*0.29 0.10

2.29** 0.10*0.48 0.09

0.88** 0.10*0.10 0.030.20 0.04

aClipping yield based on the average over three-week measurement.b ++Included control, PPD 1. 2%. and Mg 25%.*.**Significant at the 0.05 and 0.01 probability levels,

respectively.

Table 3. The analysis of variance for foliar burn rating, turf quality

and clipping yield as affected by N levels, chemical

treatments, and month applied in the 1985 and 1986 field tests

Source of

Chemicals

Control

Control

Control

Control

Control

Error A

variance

treated

vs.

vs.

vs.

vs.

vs.

Month applied

PPD

NBPT

ATS

K+

Mg++

Chemical X month

Error B

df

12

(1)

(1)

(1)

(1)

(1)

36

3

36

117

Burn

rating

0.61^

0.81*

a

0.16

0.22

0.26

0.08

0.35*

0.08

0.13

1985

Mean squares

Turf

quality

0.15**

0.12*

0.00

0.09

0.14*

0.05

1.22**

0.05*

0.03

Clipping

yield

267.45

117.97

0.29

40.75

310.66

166.59

34274.56**

39.52

152.88

df

15

(1)

(1)

(1)

(1)

(1)

45

3

45

144

Burn

rating

0.29*

0.26

0.22

0.00

0.05

0.42*

0.12

6.94**

0.12**

0.09

1986

Mean squares

Turf

quality

0.01

0.01

0.03*

0.04*

0.06**

0.07**

0.36

5.10**

0.02**

0.01

Clipping

yield

511.21

1036.25**

1355.48**

350.73*

98.40

0.28

338.19

9937.80**

44.18

57.25

**

^o data available in 1985.

•,••Significant at the 0.05 and 0.01 probability levels, respectively,

46

Table 4. The effect of chemical treatments on clipping yield over afour-week period following fertilization of Kentucky bluegrass

turf with liquid urea at 49 kg N ha-1 (1 Ib N/1000 ft2)

Clipping yielda1985 1986

Treatment June July Aug. Sep. Ave. June July Aug. Sep. Ave.

Control 44.0 93.9 78.9 47.9 66.2 84.2 58.9 62.5 74.4 70.0

PPD 1% 43.1 88.5 82.8 41.2 63.9 100.2 71.5 69.4 72.4 78.42% 48.7 94.4 80.0 42.7 66.4 109.5 79.8 71.2 80.6 85.23% 38.2 82.0 78.4 36.4 58.7 94.9 62.9 63.6 75.6 74.2

NBPT .5% b 100.3 68.9 67.9 84.0 80.3--1% 100.8 70.4 65.7 78.0 78.72% 102.0 74.8 72.9 81.8 82.9

ATS 5% 31.6 88.8 82.1 45.2 61.9 87.5 69.2 66.5 74.7 74.515% 46.0 97.6 84.9 44.7 68.3 99.1 72.1 69.8 81.2 80.625% 47.0 91.6 87.5 45.2 67.8 92.4 63.0 61.3 67.7 71.1

K+ 5% 45.9 91.3 85.5 46.9 67.4 81.8 61.3 63.2 68.5 68.715% 47.3 100.8 86.5 49.4 71.0 88.7 64.6 62.0 69.8 71.325% 43.0 90.1 81.4 48.1 65.6 92.3 70.9 71.9 79.3 78.6

Mg++ 5% 48.7 105.2 92.2 53.2 74.8 89.3 65.2 68.1 77.2 74.915% 46.5 97.1 87.8 51.1 70.6 82.6 62.8 66.4 70.9 70.625% 43.4 101.0 82.3 46.6 68.3 82.8 56.0 56.9 63.6 64.8

LSD (0.05) 9.3 LSD (0.05) 10.7

~ased on fresh weight (g/1.5 m2).

bNo data available in 1985.

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N OJ ... N-a OM ... CD - to= .-l Q) ~ OMas OM :t m OJ.j.J ... "0

A ... N .j.J ;j 1'-1~ Q) ,..-t .&oJ Q)~ ~ t,) 0 as OMbO a ... ~~ bO x: Q)

0 = ~ beOM -a .j.J

~ =.j.J

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~Nla:dI1::>

CD

Figure 2. Tbe effect of KCl treatment on visual burn and turf qualityover a four-week period following fertilization of Kentucky

bluegrass turf with liquid urea at 49 kg N ha-1 (1 lb N/IOOO

ft2)

91985

50

1986

B

~~C)z....I-<D::ZD::::JCD

7

• CONTROL X I<CL 5%• I<CL 15% 0 I<CL 25%

uz....I-<0::~I-M

-J<:J(]

B

7

6 JUNE JULY AUG. SEP. JUNE JULYMONTH TREATED

AUG. SEP.

Figure 3. The effect of MgCl2on visual burn and turf quality

over a four-week period following fertilization of Kentucky

bluegrass turf with liquid urea at 49 kg N ha-1 (1 Ib N/1000

ft2)

91985

52

1986

CtZ-.....<0::Z0:::Jm

8

7

••

CONTROLMCCLz 15%

x

oMCCL...a 5%

MCCL...a25%

7

I

6JUNE JULY AUG. SEP. JUNE JULY

MONTH TREATEDAUG. SEP.

Figure 4. Effects of PPD and NBPT on clipping yield increase (%) overthe control following fertilization of Kentuckybluegrass turf with liquid urea at 49 kg N ha-1 (1 lb N/1000ft2)

The values shown are averages of weekly measurement over afour-week period in 1986.

54

40LSD .05 = 15.0

.. NBPT .5% NBPT 1%

30NBPT 2%

Wtn<W0::UZ....

AVERAGE

~ PPO 2%.. PPO 1%

c:J PPO 3%

AUCUST SEPTEMBERMONTH APPLIEO

JULY

LSD .05 = 12.8

JUNE

30

Wtn<Wa::uz-

Figure 5. Effects of PPD and NBPT on clipping yield increase (%) ascompared with the control among the weeks followingfertilization of Kentucky bluegrass turf with liquid urea at49 kg N ha-1 (1 lb N/1000 ft2)

The values shown are averages over a four-month period in1986.

56

30LSD .05 = 15.0

• NBPT. 5% X NBPT 1%

•UJUl<UJ0::UZ....o..JUJ....>-H

oLSD .05 = 12.8

5

o.JUJ.....>-N 10

UJ(f)

<UJ~UZ

25

20

15

o WEEK 1 WEEK 2 WEEK 3WEEK MEASURED

WEEK 4