PAPER I. THE RESPONSE OF KENTUCKY BLUEGRAS S TURF TO. PHENYLPHOSPHORODIAMIDATE (PPD) AND MAGNESIUM (Mg ++) APPLIED IN COMBINATION WITH UREA

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1 4 PAPER I. THE RESPONSE OF KENTUCKY BLUEGRAS S TURF TO PHENYLPHOSPHORODIAMIDATE (PPD) AND MAGNESIUM (Mg ++) APPLIED IN COMBINATION WITH UREA

2 5 The Response of Kentucky Bluegrass Turf to Phenylphosphorodiamidate (PPD) and Magnesium (Mg++) Applied in Combination with Ureal Y. K. Joo and N. E. Christians 2 1Contribution from the Department of Horticulture. Iowa State University. Published as Journal Paper No. J-l1998 of the Iowa A.griculture and Home Economics Experiment Station. Ames. Project Graduate Research Assistant and Associate Profe.ssor. respectively. Department of Horticulture. Iowa State University. Ames. Iowa

3 6 ABSTRACT Surface-applied urea involves the risk of considerable nitrogen (N) loss to the atmosphere as gaseous ammonia (~). Among the methods that have been proposed to reduce this N loss are the application of urea with urease inhibitors or the combinations of urea with cationic materials. The objectives of this field test were to observe the effects of the urease inhibitor Phenylphosphorodiamidate (PPD) and. the effects of magnesium chloride (MgCl 2 ) on foliar burn. turf quality. and clipping yield of Kentucky bluegrass turf treated with surface-applied urea. In the heat of July. the Mg++ treatment resulted in significant foliar burn. but it reduced burn in the relatively cool temperatures of September. The fresh weight of clippings after treatment with 2% PPD was observed to increase 20 to 31%. This result indicates that 2% PPD can have an effect on the N-use efficiency of surface-applied urea on Kentucky bluegrass turf. Magnesium (Mg++) produced a 13% to 25% increase of clipping yield at the rate of 1 lb N/1000 ft 2 in August and September. but a 20% decrease at the rate of 2 lb N/IOOO ft 2 in August. This result indicates that the cation Mg++ may have a positive effect on the reduction of ammonia volatilization and increase urea nitrogen efficiency with low ++ concentration under cool-temperature conditions. However. Mg may increase phytotoxicity of fertilizer solutions at high concentrations in times of environmental stress. Additional index:words: Urease inhibitors. Cationic material.

4 7 Ammonia volatilization, Phenylphosphorodiamidate, Magnesium chloride, Foliar burn, Turfgrass.

5 8 INTRODUCTION The use of urea on turf grass areas has increased during the past 20 years, and it is now a major source of nitrogen en) for fertilization programs used on golf course.s, home lawns,. and athletic fields. Urea can be applied in dry and/or liquid forms. Because of its versatility, liquid fertilization is rapidly becoming the most popular method of applying urea to turfgrasses. Many researchers, however. have reported that the surface application of urea involves the risk of considerable N loss to the atmosphere as g.aseous 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). Laboratory studies have been conducted to investigatenh 3 volatilization from urea and the factors which affect it. Amongthese factors are the urease activity of the soil, ph, temperature, water content, ~ 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). In Torello and Wehner (1983) demonstrated that urease activity within a turf thatch layer and urease activity associated with turfgrass tissue were very high compared with activities in underlyin.g soil. Their findings suggest that, when'urea is applied to turf, the high urease levels in thatch could result in greater ~ volatilization than is normally observed in other types of crop production.

6 9 Various compounds capable of reducing gaseous loss of NH by 3 retarda tion of urea hydrolysis in soils have been studied. and many compounds have been patented as urease inhibitors (Bremner and Douglas. 1971b; Mulvaney and Bremner, 1981). Researchers at Iowa State University and the Tennessee Valley Authority have studied the effect of urease inhibitors on transformations of urea N in soils. They found that Phenylphosphorodiamidate (PPD) was the most effective urease inhibitor and have reported that it reduces ammonia volatilization and urea hydrolysis under various environmental conditions (Bremner and Douglas, 1971a, 1971b; Bremner and Mulvaney, 1978; Mulvaney and Bremner. 1981; Marten and Bremner. 1982; Hauck. 1983). East German researchers have demonstrated that PPD~proves the urea efficiency in pot experiments with oats. r:yegrass, and wheat (Heber et al., 1979; Matzel et al 1979). In 1983, workers in the Syracuse Research Laboratory studied the role of urease inhibitors in increasing efficiency of surface-applied urea and in increasing corn yield in the field. They demonstrated the greater potential for NHJ losses from reduced-tillage systems and proposed the use of urease inhibitors in keeping these losses to a minimum (Hendrickson et a1 1983; 0' Connor et al.' 1983; Omhol t and Hendrickson, 1983) Another concept concerning the reduction of mi.3 loss fran surfaceapplied urea was presented by Fenn (Fenn et al., 1981, 1982a, 1982b).. ++ NEL + dmg++ d They have stud1ed the use of Ca '_._~" K, an to re..uce ~ volatilization. In the absence of cations, all urea on the soil surface is reported to be converted to other forms of nitrogen in two to three

7 10 days. The extremely rapid conversion of urea to ammonium carbonate is believed to be responsible for the high ammonia losses. However, cations in combination with urea are believed to reduce the rate at which urea decomposes. Large quantities of urea in the presence of cations may persist on the soil surface for two or more weeks. The urea combined with cations on the soil surface is thought to be in equilibrium with water and will be immediately released into the soil during a rainfall or irrigation The objectives of this initial field test were to observe the effects of the urease inhibitor PPD and the effects of magnesium chloride on foliar burn, turf quality, and clipping yield of Kentucky bluegrass turf treated with surface-applied urea.

8 11 MATERIALS AND METHODS This study was conducted in 1984 at the Iowa State University Turf Research Plots north of Ames, Iowa. The turf used in the study had been established in 1981 on a 'Nicollet' Aquic Hapludo1l fine loamy mixed mesic soil with a ph of ppm p. 90 ppm K, and 2.3% O.M. with a blend of 25% by weight each of 'Parade', 'Adelphi', 'Glade', and 'Rugby' Kentucky bluegrass (Poa praten.sis L.). The turf was watered as needed to prevent drought stress throughout the study. The investigation was designed in a split-plot with repeated treatments and measurements on the same plot areas in four replications. The main plots included liquid urea applied at 0, 1, and 2 Ib N/l000 ft 2 The subplots included a control, PPD at 1 and 2% of the weight of N, and Mg++. in the form of MgC1 2-6H 2 0 at 25% of the weight of N. The treatments were applied monthly in June through September_ Each plot measured 25 ft 2, and each treatment was applied in the equivalent of 3 gal H 2 0/10aO ft 2 with a CO 2 backpack sprayer operated in four different directions to assure uniform application. The degree of damage to turfgrass foliage was estimated visually three days after each application. The rating scale used ranged from 1 to 9; 9 = no visual burn, and 1 = dead turf._ Data of visual quality ratings based primarily on color, uniformity, and density were collected on a weekly basis and rated on a scale of 1-9; 9 = best quality, 6 = acceptable. and 1 = poorest. Clipping weights were collected weekly for five weeks after each treatment ata 2-inch mowing height from two strips through the

9 12 center of the plots measuring 20 inches X 5 feet each. After data were collected, all plot areas were mowed at the 2-inch mowing height and clippings were removed.

10 13 RESULTS AND DISCUSSION The effects of the anmonia volatilization inhibitors on fertilizer burn varied with nitrogen rate and time of application (Table 1). In the heat of July. the MgCl 2 treatment resulted in greater foliar burn in the plots with 2 lb N/IOOO ft 2, but it reduced burn in the treatments with 1 and 2 Ib N/1000 ft 2 in the relatively wet conditions and cool temperatures of September. The PPD reduced burn significantly at 1 lb N/IOOO ft 2 in September, but those effects were not consistent across all application dates (Table I, Figure 1). Visual turf quality increased with increasing N rate, however, the effect varied with month of application (Table I, Figure 2). Plots treated with PPD at 2% of the weight of N had higher quality ratings than plots receiving other inhibitor treatments (Table 1). This effect was most evident in September, although even that effect was quite small (Figure 2). Clipping yield increased with increasing rates of N, although the response varied with month of application (Table 1, Figure 3). Where no urea was applied, there was no effect of PPD or Mg++ on clipping yield and quality of Kentucky bluegrass (Figure 2, Figure 3). The aver.age fresh weight of clippings over a five-week period in plots treated with 2% PPD increased 28% at 1 lb N/I000 ft 2 in August, 31% at 1 Ib N/1000 ft 2 and 20% at 2 Ib N/I000 ft 2 in September (Figure 3). This result indicates that 2% PPD can have an effect on the nitrogen efficiency of surface-applied urea on Kentucky bluegrass turf. Magnesium chloride

11 14 treatments showed a 13% to 25% increase of the fresh clipping yield at 1 lb N/1000 ft 2 in August and September. but a 20% decrease at 2 lb N/1000 ft 2 in August. These results indicate that the cation Mg++ may have a positive effect on urea nitrogen efficiency with low concentrations under cool temperature conditions. ++ However, Mg may increase phytotoxicity of fertilizer solutions at high concentrations in times of emrironmental stress.

12 15 CONCLUSIONS The results of this study do not prove that ~ volatilization was decreased by any of the inhibitor treatments; however, the positive ++ effects of the 2% PPD and the Mgtreatments on the clipping yield and turf quality would indicate that. under some c.onditions. 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. More detailed studies are under way to further measure the effects of these treatments on turfgrass growth and quality and to measure the quantity of NHJ volatilized from turfgrass areas treated with these materials.

13 16 LITERATURE CITED Bremner, J. M., and L. A. Douglas. 1971a. Decomposition of urea phosphate in soils. Soil Soc. Am. Proc. 35: Bremner, J. M., and L. A. Douglas. 1971b. Inhibition of urease activity in soils. Soil Biol. Biochem. 3: Bremner, J. M., and R. L, Mulvaney Urease activity in soils, p In R. G. Burns (ed.). Soil Enzymes. Academic Press, London. Ernst, J. W., and H. F. Massey The effects of several factors on volatilization of ammonia formed from urea in the soil. Soil Soc. Am. Proc. 24: Fenn, L. B., J. E. Matocha, and E. Wu. 1982a. Soil cation exchange capacity effects on ammonia loss from surface-applied urea in the presence of soluble calcium. Soil Sci. Soc. Am. J. 46: Fenn, L. B., J. E. Mathocha, and E. Wu. 1982b. Substitution of ammonium and potassium for added calcium in reduction of ammonia loss from surface-applied urea. Soil Sci. Soc. Am. J. 46: Fenn, L. B., R. M. Taylor, and J. E. Mathocha Influence of soluble calcium and magnesium on ammonia losses from surface applied nitrogen fertilizers: General Theory. Soil Sci. Soc. Am. J. 45: Gasser, J. K. R Urea as fertilizer. Soils and Fertilizers 27: Hargrove, W. L., and D. E. Kissel Ammonia volatilization from surface applications of urea in the field and laboratory. Soil Sci. Soc. Am. J. 43: Hauck, R. D Urease inhibitors - current status. Proc. Annu. Meet. Fert. Ind. Round Table. Baltimore, MD. Fertilizer Industry Round Table pp Heber, R., S. Mueller, W. Matzel, and H. Ansorge Ammonia losses in urea fertilization. Part 4. Archiv Acker- Pflanzenbau Bodenkd. 23: Hendrickson, L. L., T. I. Omholt, and M. J. 0*Connor Role of urease inhibitors in increasing efficiency of surface-applied urea. Agron. Abstr. 1983:156. Marten, D. A., and J. M. Bremner Use of phosphoroamides for

14 17 retardation of urea hydrolysis in soils. Agron. Abstr. 1982:192. Matzel. W S. Mueller. H. Lippold. and R. Heber Effect of the urease inhibitor phosphoric acid phenylesterdiamide on the use of urea nitrogen in top-dressing of summer wheat and oats. Archiv Acker- Pflanzenbau Bodenkd. 23: Mulvaney. R. L and J. M. Bremner Control of urea transformations in soils. p In E. A. Paul and J. M. Ladd (ed.). Soil Biochemistry. Vol. 5. Marcel Dekker. Inc New York. O'Connor. M. J P. M. Falk. and L. L. Hendrickson Effect of soil temperature and plant residue on ability of PPD to reduce ammonia volatilization. Agron. Abstr. 1983: 159. Omhol t. T. E and L. L. Hendrickson Ability of PPD to reduce ammonia volatilization and increase corn yields in the field. Agron. Abstr. 1983:215. Overrein. L. N and P. G. Moe and ammonia volatilization in soil. 61. Factors affecting urea hydrolysis Soil Sci. Soc. Am. Proc. 31:57- Tomlinson. T. E Urea: Agronomic applications. Proc. Fertil. Soc. 113:1-76. Torello. W. A and D. J. Wehner Urease activity in a Kentucky bluegrass turf. Agron. J. 75: Volk. G. M Volatile loss of ammonia following surface application of urea to turf or bare soils. Agron. J. 51:

15 18 Table 1. The analysis of variance for burn rating, turf quality, and clipping yield as affected by nitrogen levels. inhibitors (PPD. ++ Mg ) and month treated Mean Squares Burn Turf Clipping Source of variance df rating quality yield Nitrogen levels ** ** ** Inhibitors * 2054 * vs. Control Mg ++ (1) Control VB. PPD 1% (1) Control VB. PPD 2% (1) ** 552 ** Nitrogen X inhibitors Month treated ** 4.26 ** ** Month X nitrogen ** 2.21 ** 2910 ** Month X inhibitor ** Month X N X inhibitor * *. **Significant at the 0.05 and 0.01 probability levels. respectively.

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17 o FOLIAR BURN 1984 INHIBITORS CONTROi Q O p p JX f» f» B 2X...,* Ms 2 5%. m 8 * c i 7.0 "5 6.0 a * 5.0 NO Nl N2 NO Nl N2 June July X NO Nl N2 NO Nl N2 August September

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19 22

20 Liquid urea was applied at 0 (NO). 1 lb N/1000 ft 2 (Nl), and Clipping yields are based on fresh weight from the area of Figure 3. The effects of inhibitors on clipping yield of Kentucky bluegrass turf treated with surface-applied urea 2 lb N/1000 ft 2 (N2) ft 2 (1.5 m 2 ).

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