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Published online 30 July 2007
Published in Crop Sci 47:1628-1634 (2007)
© 2007 Crop Science Society of America
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TURFGRASS SCIENCE-NOTES

Mowing and Nitrogen Source Effects on Ammonia Volatilization from Turfgrass

Ellen C. Knight, Elizabeth A. Guertal* and C. Wesley Wood

Agronomy and Soils Dep. Auburn Univ., 201 Funchess Hall, Auburn, AL 36849

* Corresponding author (eguertal{at}acesag.auburn.edu).


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Although NH3 volatilization can be a pathway of N loss from turfgrass systems, the magnitude of this loss has not been well quantified, especially from N sources other than urea. The objective of this research was to evaluate NH3 volatilization as affected by N source and mowing of those N sources. The study consisted of mowing treatments (mowed or not mowed) and N sources: (i) urea, (ii) S-coated urea, (iii) polymer-coated urea, (iv) methylene urea, (v) ammonium nitrate, and (vi) composted sewage sludge. Mowing treatments were applied by mowing the N sources, which had been applied to bentgrass (Agrostis palustris Huds.) putting greens. The fertilizers were collected and taken to the laboratory for NH3 volatilization measurements, without additional watering. Treatments were applied at an N rate of 14.7 g m–2 to the surface of bentgrass plugs contained in 1-L jars. Ammonia volatilization over 10 d was measured via boric acid trapping. Two experiments were conducted: one with loamy sand (Exp. 1) and one with an 80:20 sand–peat (v/v) greensmix (Exp. 2). In Exp. 1, mowing never affected NH3 volatilization, so mowing was eliminated from Exp. 2. Over the 10-d measurement period, urea had greatest total NH3 volatilization, with most released in the first 2 d. Polymer-coated urea released the least NH3, with greatest release 9 and 10 d after treatment. In descending order, amounts of NH3 volatilization were urea, S-coated urea, methylene urea, composted sewage sludge, ammonium nitrate, and polymer-coated urea.

Abbreviations: IBDU, isobutylidene diurea • SCU, S-coated urea • SGN, size guide number


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
LOSSES OF N from agricultural systems have long been studied, with the loss pathways of denitrification, volatilization, plant uptake, leaching, NH3 fixation, and immobilization all receiving scrutiny in a wide range of agricultural systems. In turfgrass, losses of N via leaching (Brown et al., 1977; Starr and DeRoo, 1981; Morton et al., 1988; Mancino and Troll, 1990; Geron et al., 1993; Miltner et al., 1996; Pare et al., 2006; Frank et al., 2006) and clipping removal (Johnson et al., 1987; Bowman et al., 2002; Kopp and Guillard, 2002; Fagerness et al., 2004) have been studied most intensively. Despite real environmental concerns, pathways of gaseous loss of N (volatilization and denitrification) have been less studied in turfgrass systems. Environmental issues associated with NH3 volatilization include NH3 deposition (Rao et al., 1993), eutrophication (Boyd, 2000), and odor concerns from application of animal manures (Moore et al., 1995).

Ammonia volatilization is most likely to occur when urea is applied to the surface of turf, where the urea hydrolyzes in the presence of water and urease to form NH4 (Torello et al., 1983; Kissel and Cabrera, 1988). This NH4 can be converted to gaseous NH3, which may be lost to the atmosphere via volatilization. Factors that increase NH3 volatilization include increased soil pH (Clay et al., 1990; He et al., 1999; Fan and MacKenzie, 1993), increased soil temperature (Clay et al., 1990; He et al., 1999; Titko et al., 1987), increased soil water content (Bouwmeester et al., 1985; McInnes et al., 1986; Ferguson and Kissel, 1986), and increased wind speed (Sommer et al., 1991; Ferguson and Kissel, 1986).

Method of fertilizer application and fertilizer source also affect NH3 volatilization. When NH3 volatilization from turf was studied, selected N sources were urea (Bowman et al., 1987; Nelson et al., 1980; Sheard and Beauchamp, 1985; Titko et al., 1987; Torello et al., 1983), isobutylidene diurea (IBDU) (Nelson et al., 1980), S-coated urea (SCU) (Torello et al., 1983), and ureaformaldehyde (Torello et al., 1983). Typically, fertilizers were applied as granular materials, with the presence or absence of irrigation (Titko et al., 1987; Bowman et al., 1987) or the inclusion of liquid urea formulations (Volk, 1959; Torello et al., 1983; Wesely et al., 1987; Titko et al., 1987) as treatment variables. Although turf-type fertilizers were included in some additional studies, they were not applied to turf, but rather to bare soil (Hargrove and Kissel, 1979; Kissel and Cabrera, 1988) or pasture grasses (Hargrove and Kissel, 1979; Lightner et al., 1990). Such results, while valuable, may not directly apply to the specialized environments of closely mown turf.

Methodologies for measuring NH3 volatilization from turf varied, but in most cases they were short-term studies (3–21 d; Petrovic, 1990) which utilized laboratory or greenhouse methods or small-scale field devices. A typical collection device used a chamber to hold fertilized soil or turf, a trap to collect volatilized NH3, and a vacuum pump to pull air through (Hargrove and Kissel, 1979). Because nonfield and closed system field studies prevented normal air movement across the turf surface (Hargrove and Kissel, 1979), results from such closed experiments were typically used to compare treatment effects (Petrovic, 1990), and quantified N loss over a short period of time.

There are no published studies which have examined NH3 volatilization from warm season turfgrasses. In fact, the published research has been conducted on one species: Kentucky bluegrass (Poa pratensis L.). Rates of NH3 volatilized from a Kentucky bluegrass turf ranged from 1.1 to 10.3% of applied N, with the greater amount volatilizing from urea, and less from a SCU product (Torello et al., 1983). Volatilization was greater when the same rate of urea (49 kg ha–1 N) was applied as a liquid spray, compared to a prill formulation (Torello et al., 1983). Conversely, others found greater volatilization from urea applied in a granular form as compared to that applied in a solution, except when irrigation immediately followed the urea application (Titko et al., 1987). In these 84-h greenhouse studies using Kentucky bluegrass, as much as 60% of applied N was lost via volatilization, when temperatures and relative humidity were high (32°C and 68%), and the turf was not irrigated after application (Titko et al., 1987). When irrigation followed the urea application NH3 volatilization was reduced to 2% of total N applied (Titko et al., 1987). When urea was applied to Kentucky bluegrass as a foliar application at 1.7 and 3.4 g m–2 N, volatilized N was 35 and 31% of the total applied, respectively, with maximum NH3 losses occurring at 25 h after treatment (Wesely et al., 1987). As little as 1.0 cm of irrigation water reduced such volatilization losses from spray-applied urea, with 5 cm of irrigation reducing volatilization losses to around 1% of total N applied (Bowman et al., 1987). Volatile loss of NH3 from urea sprays applied to Kentucky bluegrass was relatively small (<10%), and most loss occurred within the first 8 h. Reductions in volatile loss of NH3 between 8 and 21 h after application were hypothesized as the result of biological immobilization of applied N (Bowman and Paul, 1990).

In summary, N losses from NH3 volatilization in turfgrass systems have been shown to vary from almost zero to as great as 60% of total N applied. Losses were greatest when irrigation was not applied following application (Titko et al., 1987) and when volatilization from thatch was separated from soil (Nelson et al., 1980). When slow-release fertilizer sources were evaluated, volatilization losses of NH3 from IBDU and SCU were 2% of total N applied, much less than measured in comparable urea treatments (Nelson et al., 1980; Torello et al., 1983).

There are no published studies that examine the impact of mowing on NH3 volatilization, especially on close-mown turf such as putting greens. Mowing may have a direct impact on turf fertilizers, as high quality turfgrass management on putting greens combines low mowing heights and specialty fertilizers such as resin-coated ureas. Previous research has shown that such fertilizers are susceptible to pickup via clipping removal (Mancino et al., 2001). In that work, total percentages of fertilizers lost via clipping removal ranged from 75.4 to 1.9%, with fertilizer loss being most related to water solubility. Coated and organic products were most likely to be collected in clippings (Mancino et al., 2001). If such fertilizers could be removed via mowing, our hypothesis is that the products could be nicked or chipped in the mowing process, especially in the first few mowings when fertilizer prills are sitting higher in the turf canopy and have not moved into the underlying canopy. Coated urea products that have been chipped might be prone to increased N loss from NH3 volatilization, as exposed urea would be sitting on the turf surface.

Thus, the objectives of this study were to determine the effects of mowing fertilizer prills on NH3 volatilization from fertilizers applied to turfgrass, and to determine differences in volatilization among N sources that have not been evaluated in previous research. This study was intended as an initial assessment of potential NH3 volatilization losses in the first 10 d after mowing and not to quantify losses over the entire release period of a slow-release fertilizer source.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Two experiments were performed. Both included the same six fertilizer sources (Table 1), plus an unfertilized control. Coated or slow-release products were specifically sized for application to low-cut turf such as putting greens. The other products (SCU, ammonium nitrate, and urea) were not sized as greens grade fertilizers (Table 1).


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  		Table 1. Nitrogen sources used in the laboratory examination of NH3 volatilization.

 
The first experiment was conducted using 10-cm-diameter cores collected from a 4-yr-old Marvyn loamy sand (fine-loamy, kaolinitic, thermic Typic Kanhapludult) putting green with ‘G-2’ creeping bentgrass. A total of 16 cores were extracted using a conventional cup cutter, and soil removed so that a 2.5-cm layer remained below the thatch. Average thatch depth of cores was 1.3 cm, underlying soil pH was 6.0, soil cation exchange capacity was 2.0 cmolc kg–1, and average soil-water content was 15.9%. Cores were removed the morning (after dew had dried) that mowing treatments were applied, and cores were moved to the laboratory for subsequent fertilizer treatment applications. This same procedure of core removal and transport to the laboratory was also used for Exp. 2, except those cores were removed from a 3-yr-old putting green of 80% sand and 20% reed–sedge peat (v/v). Average thatch depth of those cores was 1.0 cm, underlying soil pH was 5.9, soil cation exchange capacity was 1.8 cmolc kg–1, and average soil-water content was 15.3%.

In Exp. 1, mowing was a treatment variable. To apply this treatment, the N sources were applied to the surface of the same putting green from which the cores had been removed. The six fertilizer sources (Table 1) were hand spread in six individual blocks (2 by 2 m) at a rate to ensure that fertilizer prills could easily be detected for removal from the green (an N rate of approx. 30 g m–2). Half of each block (1 by 2 m) was mowed by making seven passes across the block, simulating a week of mowing. These seven passes were applied at one time, using a Toro walking greens mower (Toro Company, Bloomington, MN) with a 3.2-mm mowing height, without grooming reels or clipping collection baskets. The other half of each block remained unmowed, with fertilizers on the surface. Both mowed and unmowed N sources were collected with a small air vacuum immediately after the seven mowing passes were applied, stored in sealed glass jars, and immediately transferred to the lab for application to the surface of the previously harvested cores. No additional irrigation was applied after fertilizer application, nor was any additional water applied during the 10-d experiment period.

Harvested grass cores were placed into 1-L glass canning jars, with the turf lying flat in the bottom of each jar. The volatilization experiment was conducted on a lab bench with 24-h standard room lighting, and no additional environmental modifications. Average room temperature during the experiment was 27.4°C. Due to the nature of the experiment (sealed glass jars with no ability to trim the turf) the experiments were conducted for a 10-d period only. This is a typical time length for volatilization experiments, as previous research demonstrated most NH3 release within the first days of experiment initiation (Petrovic, 1990). Fertilizers collected from the unmowed and mowing treatments were applied by hand at 14.7 g m–2 of N across the top of the turf surface in each jar.

The seven N sources and two mowing treatments were combined factorially, and two empty jars for determining background NH3 were included, resulting in 16 experimental units per replication. There were four replications of each experiment, with replication occurring over time in the controlled laboratory setting.

Exp. 2 was conducted exactly as Exp. 1, except that the mowing treatment was eliminated. This was because mowing never affected NH3 volatilization in Exp. 1, so it was eliminated as a treatment variable in Exp. 2.

To collect NH3, an NH3 trap system was used, following the method of O'Halloran (1993). A schematic is shown in Fig. 1 . Air flow was generated by passing 1000 mL min–1 air stream through a 2.5 M sulfuric acid air scrubber and across each jar, with resultant NH3 trapped in 100 mL of 0.003 M boric acid. The boric acid trap was changed each day for 10 d, with collected samples titrated to the original pH of the boric acid using 0.005 M sulfuric acid. Mass and percentage of volatilized NH3 were calculated using the formulas:

Formula 1[1]
where 14 is the equivalent weight of N, and

Formula 2[2]
where 118 is the milligrams of N per jar.


Figure 1
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  		Figure 1. Diagram of complete laboratory set up with jars, pump, and air scrubbers, following the procedure of O'Halloran (1993). The glass manifold is connected to an opening in each jar with silicon tubing.

 
In the laboratory, treatments were arranged in a complete randomized design, with the empty background jars also included in that randomization. The data was analyzed using standard statistical procedures (SAS Institute, 2006), with analysis of variance used to test for the significance of treatment effects (N source, mowing) and their interaction. Means separation (Duncan's) or use of standard error bars were used to determine differences in NH3 volatilization as affected by N source, with a P value of 0.05.


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Background NH3 was never detected at any measurable level at any time during the experiment period. In Exp. 1, mowing never affected NH3 volatilization (Fig. 2 ) (nor was the interaction of mowing and N source significant), so mowing was eliminated from Exp. 2. There was a nonsignificant trend for greater volatilization in the mowed SCU treatments, as compared to SCU treatments that were not mowed. This fertilizer material was the only coated product that had a larger size guide number (SGN), which is defined as the average particle size in millimeters multiplied by 100 (Table 1). In practice, a material with a larger SGN would not have been applied to a close mown surface such as a putting green. Although not significant, this result does suggest that the impact of fertilizer prill size on N losses by volatilization should be examined in greater detail.


Figure 2
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  		Figure 2. Effect of mowing (M) and N source on percent N volatilized in Exp. 1. Mean comparisons are only within each fertilizer (mowed or unmowed), and not across N sources. There was no significant difference in NH3 volatilization due to mowing. AN, ammonium nitrate; SCU, S-coated urea.

 
In both experiments N source significantly affected NH3 volatilization (Fig. 3 and 4 ). In both experiments significant loss of N occurred from only two N sources, urea and SCU, and the majority of this loss occurred in the first 4 d after experiment initiation. Such results are consistent with previous work, which showed that N losses from volatilization mostly occurred within the first few days of experiment initiation (Nelson et al., 1980; Torello et al., 1983; Petrovic, 1990).


Figure 3
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  		Figure 3. Ammonia volatilization as affected by N source and sampling day, Exp. 1. Vertical bars are the standard error. AN, ammonium nitrate; SCU, S-coated urea.

 

Figure 4
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  		Figure 4. Ammonia volatilization as affected by N source and sampling day, Exp. 2. Vertical bars are the standard error. AN, ammonium nitrate; SCU, S-coated urea.

 
Although losses of N due to volatilization are often greater in soils with a higher pH (Bouwmeester et al., 1985; He et al., 1999), losses observed in our study occurred from treatments applied to soils with pHs of 5.9 and 6.0. Ammonia volatilization from acid soils is consistent with previous findings, where volatile loss of N was measured from two soils with pHs of 5.2 and 6.0 (Fan and Mackenzie, 1993). In that work it was noted that there was less N volatilized from the soil with a pH of 5.2 than from the soil with a pH of 6.0. Others have observed N loss due to volatilization from soils or turfed soils with initial pHs of 6.8 (Clay et al., 1990) and 6.0 (Lightner et al., 1990), respectively.

Urea released the greatest amount of NH3, with 40.0 and 35.5% of applied N lost via volatilization in Exp. 1 and 2 over the 10-d period, respectively (Fig. 5 and 6 ). Such amounts are similar to that reported in previous research, with N loss ranging from 0 to 61% of total N applied (Petrovic, 1990). Research with higher percent N losses (35–39%) typically occurred in studies in which irrigation was not applied, or only lightly applied after application (Bouwmeester et al., 1985; Wesely et al., 1987). In our study, irrigation was not applied after fertilizer application, which would account for the relatively high N loss in some treatments.


Figure 5
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  		Figure 5. Total cumulative N loss due to NH3 volatilization over a 10-d period as affected by N source, Exp. 1. Columns with different letters are significantly different from each other at {alpha} = 0.05. AN, ammonium nitrate; SCU, S-coated urea.

 

Figure 6
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  		Figure 6. Total cumulative N loss due to NH3 volatilization over a 10-d period as affected by N source, Exp. 2. Columns with different letters are significantly different from each other at {alpha} = 0.05. AN, ammonium nitrate; SCU, S-coated urea.

 
In Exp. 1, at the end of 10 d, mean volatilization loss of NH3 from urea and SCU were not different (Fig. 5). In Exp. 2, urea and SCU differed in the amount of NH3 volatilized (Fig. 6). Compared to other slow-release sources, greater loss of N from SCU in Exp. 1 might be the result of an uneven coating process, or loss of N from cracks or fissures in the prills. In both experiments urea had significantly greater loss of NH3 than polymer-coated urea, ammonium nitrate, methylene urea, or composted sewage sludge (Fig. 5 and 6).

Polymer-coated urea released the lowest total percentage of applied N, but the amount was not significantly different from that released from methylene urea, ammonium nitrate, or composted sewage sludge (Fig. 5). When N was volatilized from polymer-coated urea (Exp. 1) it was released at 9 and 10 d after treatment, but it was small (0.76% of total N applied) and not different from the control. Delayed NH3 volatilization from slow-release products was also noted in an earlier study with the slow-release product SCU, where slight amounts of NH3 were released from SCU-treated turf for up to 21 d after application (Torello et al., 1983). In Exp. 2, there was no measurable NH3 volatilization from the polymer-coated urea (Fig. 6).

The slight evidence offered in this paper (resin coated) and one other (Torello et al., 1983) that slow-release sources might continue to release N for volatilization suggests that new methods for long-term measurement of NH3 volatilization in turf should be developed. Current methods that could be used in an 8-wk experiment could only be adjusted for bare soil, as the closed chamber system does not allow for watering or turf maintenance. This limits the inclusion of treatment variables such as mowing or irrigation regimes. Large-scale field systems (Wood et al., 2000) or modification of a system used for denitrification measurement (Horgan et al., 2002) may offer a solution, and research is currently underway to test this hypothesis.


   CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Nitrogen loss via NH3 volatilization was affected by N source, but not mowing, in our 10-d laboratory evaluations. Nitrogen sources with greatest N loss were urea and SCU, with only negligible amounts lost from ammonium nitrate, polymer-coated urea, methylene urea, or composted sewage sludge. In both experiments only two N sources, urea and SCU, had N losses greater than the control, and the majority of this loss occurred in the first 4 d after experiment initiation. Levels of N lost via volatilization were similar in both the native loamy sand putting green and the 80:20 sand–peat greensmix. Our laboratory method precluded long-term evaluation; but the slow-release nature of products such as polymer-coated urea and methylene urea would make 8 to 12 wk evaluations the next step of this research.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.

Received for publication September 22, 2006.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 




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