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a Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias (INIFAP), Apartado Postal 247, Torreón, Coahuila 27000, México
b Dep. of Agronomy and Horticulture, New Mexico State Univ., Las Cruces, NM 88003
c Dep. of Economics and International Business, New Mexico State Univ., Las Cruces, NM 88003
Corresponding author (hmquiroga{at}yahoo.com)
Received for publication November 30, 1999.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSIGNIFICANCE AND APPLICABILITY...REFERENCES |
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Abbreviations: HYD, Hydroform • SCU, sulfur-coated urea • URE, urea
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSIGNIFICANCE AND APPLICABILITY...REFERENCES |
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Turfgrass NO3 leaching potential is highly variable, owing to its strong dependence on multiple factors, including irrigation practice, soil texture, solubility of N source, N application rates, and the growth rate, stand maturity, and corresponding N demand of the grass (Spalding and Exner, 1993). For example, overwatering with fertilization may generate NO3–N leaching pollution problems, but proper water management and curtailing of N fertilization during periods of slow growth reduce NO3–N leaching risk (Liu et al., 1997; Morton et al., 1988; Mosdell and Schmidt, 1985; Rieke and Ellis, 1973; Snyder et al., 1977, 1984). In addition, well-established turfgrass stands have an increased capacity to use soil-applied N compared with newly planted turfgrass (Hesketh et al., 1995). Such capacity has been elaborated in other studies and has been attributed to N immobilization in the thatch layer (Miltner et al., 1996; Nelson et al., 1980), but presumably would also be due to increased N uptake capability as the turfgrass develops greater density following initial establishment.
Use of slow-release N sources will reduce the risk of leaching-induced NO3–N contamination of drinking water sources, N volatilization, and fertilizer burns, and will allow fewer applications at higher rates (Hummel and Waddington, 1981). In bermudagrass fertilized at 5 g N m-2 mo-1 with SCU (30% dissolution rate at 7 d), NO3–N leaching concentration was under the USEPA limit (10 mg L-1), regardless of the irrigation method and frequency (Snyder et al., 1984). However, this study showed that irrigation with a highly soluble N source (NH4NO3) produced leachate NO3–N concentrations three to seven times greater than the USEPA limit during the period 10 to 25 d after treatment. A similar observation comparing isobutylidene diurea (IBDU) and NH4NO3 was reported in cool-season grasses such as Kentucky bluegrass (Poa pratensis L.), perennial ryegrass (Lolium perenne L.), and tall fescue (Festuca arundinacea Schreb.) (Brown et al., 1982).
The available data on turfgrass N uptake and NO3 leaching appears to be dominated by work with cool-season turfgrasses. The findings of these studies are difficult to compare because they have been collected under different conditions, such as soil types, grass species and use, water regimes, field and greenhouse environments, and fertilizer N sources (Petrovic, 1990). Moreover, these studies cannot be applied to warm-season grasses in semiarid climates such as New Mexico. Cities in the southwestern U.S. semiarid region are experiencing rapid growth of their urban populations, with ongoing development of golf courses, city parks, home lawns, athletic fields, and other recreational areas. Therefore, more information about fertilizer N fate in warm-season grasses, such as bermudagrass, is needed (Petrovic, 1990), particularly to study the environmental effect of this intensively managed system on ground water quality.
Our intent was to evaluate the growth, quality, N uptake, and N losses of bermudagrass receiving different sources of N varying in their solubility. In this paper, we discuss the effects of N source, rate, application frequency, and season of year on N recovery, plant N partitioning, and N losses.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSIGNIFICANCE AND APPLICABILITY...REFERENCES |
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The first experiment was conducted from 27 Jan. to 29 May 1997. In order to increase photoperiod, artificial light was applied using high-pressure sodium lamps at 1630 to 2000 h to provide a photoperiodic range of 12.93 to 14.97 h (hereafter referred to as long-day conditions). Artificial light intensity ranged from 250 to 300 µmol m-2 s-1, and natural light from 550 to 1200 µmol m-2 s-1 as measured by a quantum sensor (LI-189; LI-COR, Lincoln, NE). Greenhouse temperatures ranged from minima of 12.1 to 22.0°C and maxima of 22.0 to 42.0°C (Table 1). Two gas heaters were used.
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For both experiments, Tifgreen bermudagrass plugs were washed in tap water to remove all soil, then roots were trimmed to 5 cm in length from the thatch layer. Plugs were placed on the top of the medium (see below) in PVC cylinders (pots) measuring 15.24 cm in diameter and 30 cm in length. Plugs were planted on 12 January for Exp. 1 or 8 July for Exp. 2, irrigated with tap water, and mowed at a height of 1.5 cm every 5 d until the beginning of fertilization treatments (27 January for Exp. 1 and 23 July for Exp. 2). Pot bottoms were covered with plexiglass, and in the center of each cover, a 1-cm-diam. hole was drilled for drainage. The bottom 2.5 cm of each pot was filled with coarse gravel, and the remaining space was filled with growing medium consisting of a 3.8-kg mixture of builder's grade sand and peat moss (93:7 w/w). The Kjeldahl N concentration in peat was 7.8 g kg-1 (dry weight) (Bremner, 1996).
Deionized water was used for irrigation. A total of 6.0 and 5.6 L (34.2 and 31.9 cm equivalent depth of water) per pot were applied for Exp. 1 and 2, respectively. The leaching fraction averaged 5.25% for Exp. 1 and 9.05% for Exp. 2. Irrigations were applied every other day. Three N sources were evaluated: (i) URE, 460 g N kg-1; (ii) SCU, 390 g N kg-1 and 120 g S kg-1 (N dissolution rate of 30–40% at 7 d); and (iii) HYD, 380 g N kg-1 (110 g N kg-1 as water-soluble N from urea, methylene diurea, and dimethylene triurea, and 270 g N kg-1 as water-insoluble N from methylene urea). Fertilizer particle size was standardized, and only those particles that passed through a 10 mesh (2-mm pore size) and held by an 18 mesh (1-mm pore size) were used.
All N sources were broadcast at two rates (100 and 200 kg N ha-1) and at two frequencies (every 20 and 40 d). These treatments provided a range in N applications of between 300 and 1200 kg ha-1 120 d-1. An extra pot with no added N was placed within each replication (0 N control). A supplemental nutrient solution (without N) was applied at 20 mL per pot every 20 d, and included the following rates for macronutrients (kg ha-1): K (162), P (128), S (51), Ca (45), and Mg (38), plus a complete micronutrient supplementation (Turner and Hummel, 1992).
Clippings were cut with scissors every 3 or 4 d, keeping a cutting height of 1.5 cm. To remove and collect the clippings, pots were placed horizontally during the cutting process. Clippings were dried in a forced-air oven at 60°C for 48 h, weighed, and ground to pass through a 40 mesh (0.425-mm pore size). At the end of each experiment, the plugs were washed and separated into verdure (shoot material remaining after cutting) and thatch plus roots. These fractions were dried at 60°C for 72 h, weighed, and ground as described for the clippings. The sand and peat moss medium was air-dried, ground with a mortar and pestle, sieved using a 60 mesh (0.250-mm pore size), and a subsample was prepared for total Kjeldahl N analysis.
Total N content in the plant components (clippings, verdure, and thatch plus roots) and medium was measured. Thatch plus root consisted of stolons, rhizomes, true roots, and dead plant tissue. Nitrogen was extracted by the Kjeldahl acid digestion method (Bremner, 1996) using 0.2 g and 1.0 g for the plant and medium samples, respectively. Analyses were made colorimetrically for NH4–N concentration using an automated Technicon Autoanalyzer II (Technicon Instruments, Tarrytown, NY). Leachates were collected and pooled during six periods through each experiment (20-d intervals) and analyzed colorimetrically for NO3–N concentration by the cadmium reduction column method using the autoanalyzer (Technicon Instruments Corporation, 1973).
The treatments were arranged in a 3 x 2 x 2 factorial (three N sources, two rates, and two frequencies) and distributed in a randomized complete block design with three replications. Clippings were pooled together every 20 d (six periods in total) to allow sufficient dry matter for tissue analysis. Nitrogen analyses were considered as repeated measurements and the Huynh–Feldt conditions were tested. Because the Huynh–Feldt conditions were satisfied, these data were analyzed as a split-plot (SAS Institute, 1990). The main plot was the 3 x 2 x 2 factorial and the period factor (total of six) was the subplot.
Plant samples were evaluated for N concentration, total N yield, N partitioning among tissues, and N recovery. Before the treatments started, a representative pot was removed and analyzed for N content of plant (verdure and thatch plus root) and growing medium fractions. This N value was considered as the initial N status in the system and was used for the N recovery estimation.With limited exceptions, there were no interactions among the main factors of N source, rate, and frequency. Thus, N sources were averaged across rates and frequencies, rates across sources and frequencies, and frequencies across sources and rates.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSIGNIFICANCE AND APPLICABILITY...REFERENCES |
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In both experiments, significant interactions among periods were found. In the 40-d frequency (but not 20-d frequency), clipping N concentration for all sources and rates showed a cyclical pattern (Fig. 1). That is, clipping N concentration (and growth) declined as medium N was gradually depleted at the end of each 40-d period. During the second experiment (decreasing photoperiod), differences among the N sources tended to narrow, as bermudagrass growth declined with the onset of autumnal environmental conditions. In addition, the characteristic cyclic pattern of N concentration (40-d frequency) was virtually eliminated between the fifth and sixth periods (Exp. 2), but was plainly evident under the greater photoperiod at this time (Exp. 1).
Verdure, Thatch Plus Root, and Growing Medium
At the end of the first experiment (long-day conditions), verdure N concentration ranged between 15.0 and 31.6 g N kg-1 (averaged data not presented), and overall, was greater in pots fertilized with URE than with SCU and HYD in Exp. 1 (Table 2). In Exp. 2 (decreasing photoperiod), verdure N concentration ranged from 15.0 to 28.4 g N kg-1 (averaged data not presented), but there were no differences among the N sources. As expected, in both experiments, verdure N concentration increased with the higher N rate and frequent fertilization. Nitrogen concentration in thatch plus roots was between 11.1 and 21.1 g N kg-1 (averages not shown), with an increasing trend at the high N rate and frequent fertilization (Table 2). During Exp. 1, N source did not affect thatch plus root N concentration. In Exp. 2, however, URE resulted in a greater thatch plus root N concentration than with HYD. At the end of each experiment, statistical differences for main factor effects on growing medium N concentration were found only for frequencies in the first experiment, with the 20-d application interval providing the higher N concentration (Table 2).
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Clipping Nitrogen Yield Through Time
During the first experiment (long-day conditions), clippings removed more N at the end of the growing time (Fig. 2
, Periods 5 and 6). The low N yield during the fourth period may have resulted from relatively low greenhouse nighttime minimum temperatures (mean of 16°C). For the second experiment (decreasing photoperiod), the trend was for more clipping N yield during the first half of the experiment rather than during the second half. Thus, as growth became increasingly limited with decreasing photoperiod and temperature, parallel reduction in clipping N yield (N demand) also occurred.
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Verdure, Thatch Plus Roots, and Growing Medium
Verdure N yield in the first experiment (long-day conditions) was significantly affected by N source, rate, and frequency (Table 3). The highest average N yield was obtained with SCU and the lowest with HYD. For Exp. 2 (decreasing photoperiod), no differences among sources were detected. On average, 40% more N yield was obtained from verdure in the first experiment than in the second experiment. The high N rate and more frequent fertilization increased verdure N yield in both experiments. However, in Exp. 2, average N yield with SCU and URE was greater with the lower frequency than with the higher frequency (data not presented).
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Leachate Nitrate Nitrogen
As with clippings, leachates were pooled over six periods (20 d each) and analyzed through time. Overall trends in leaching NO3–N concentration differed between experiments (Fig. 3) . During Exp. 1 (long-day conditions), all NO3–N concentrations were below the USEPA limit of 10 mg L-1. For sources, the trend was unexpected, as the highly soluble URE showed the lowest average leachate NO3–N value, whereas the highest concentration corresponded to HYD, the least soluble source. Leachate NO3–N concentrations were not significantly affected by rate or frequency. For periods, there was no apparent trend, except that the low leachate NO3–N concentration at Period 3 preceded a measurable average increase in leachate NO3–N concentration at Period 4, which corresponded to the transient reduction in clipping N demand.
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All the possible interactions occurred in Exp. 2. For example, the source x period interaction occurred largely at the end of the growing season, when leaching NO3–N values with SCU and URE (high N rate) rose to levels 10 to 20 times the standard limit under the 20-d fertilization frequency. A similar range was observed with cool-season species (Brown et al., 1982), although the bermudagrass study by Snyder et al. (1984) did not show leachate NO3–N levels greater than the USEPA limit. At the end of Exp. 2 (Periods 5 and 6), the observed increases in NO3–N leachate concentration probably occurred because bermudagrass N uptake decreased as the grass was progressing into its dormancy period.
Nitrogen Removal and Recovery
Nitrogen removal by the plant (clippings, verdure, and thatch plus roots) is presented in Table 4 as total N removal and adjusted N removal (adjusted for initial N content in verdure and thatch plus roots prior to the beginning of fertilization treatment). Plant N removal was greater in Exp. 1 than in Exp. 2, since Exp. 1 was conducted under long-day conditions and higher minimum temperatures, which resulted in greater plant growth, and therefore increased plant N uptake. For both experiments, N source, rate, and application frequency significantly acted upon plant N removal. On average, adjusted plant N yields were 53.2 and 45.2 g m-2 for Exp. 1 and 2, respectively. In both experiments, there was more N yield for SCU and URE than for HYD, and greater N yield at the higher N rate and frequency. Only main factor effects were found, with no interactions.
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The interaction source x rate for total plant N recovery occurred in both experiments (Fig. 2). In the first experiment, N recovery substantially increased with increased HYD rate under both 20-d and 40-d application frequencies. This increase was less noticeable with SCU and URE. The responsiveness to HYD may have resulted from the low N availability of this highly insoluble N source, with a temporal plant N deficiency stress at the end of the 40-d period. Once the new N application was made, bermudagrass N uptake and recovery apparently increased above the average in the other treatments (Bowman et al., 1989; Hole et al., 1990).
Total plant N recovery estimates were made without a labeled N isotope, and N recoveries occasionally rose above 100% due to measurement errors. However, the average total plant N recoveries from the fertilizer (Table 4) were 84 and 77% in Exp. 1 and 2, respectively. These values are somewhat greater than those reported in cool-season turf species. For example, Starr and DeRoo (1981) reported total plant 15N recovery values of approximately 50 to 60% [from applied (NH4)2SO4] in a Kentucky bluegrass–red fescue (Festuca rubra L.) mixture. Similarly, Miltner et al. (1996) found that 66% of the applied 15N-labeled urea fertilizer to Kentucky bluegrass was recovered by the whole plant, with about 50% found in clippings.
There was a greater percentage of applied fertilizer N recovery with SCU and URE than with HYD with the lower N rate and less frequent fertilization (Exp. 2 only). Greater recovery efficiency with the lower N rate is consistent with findings reported on Kentucky bluegrass and Chewing's fescue [Festuca rubra L. subsp. fallax (Thuill.) Nyman] (Hesketh et al., 1995).
Partitioning of Plant Nitrogen
Of the adjusted plant N removal, an average of 58 to 60% of the total plant N was found in clippings, 12 to 16% in verdure, and 24 to 30% in thatch plus roots (Table 5). Nitrogen source affected the N partitioning only in Exp. 1 (long-day conditions), in that there was more total plant N in clippings using SCU and URE than with HYD, whereas the reverse occurred with verdure and thatch plus root N. Thus, with greater N availability (e.g., SCU and URE), more N was diverted to clippings. Under lower N availability (HYD), the N was directed to verdure, thatch, and roots (Adams et al., 1973; Bowman et al., 1989), because the low solubility and reduced N availability of HYD was associated with reduced clipping biomass production and N demand. The decreasing photoperiod and temperature in the second experiment limited these bermudagrass responses to the different N sources.
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SIGNIFICANCE AND APPLICABILITY OF FINDINGS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSIGNIFICANCE AND APPLICABILITY...REFERENCES |
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There is a scarcity of technical data on factors governing fertilizer N use efficiency and losses in warm-season turfgrasses. In this report, we provided quantitative information that will contribute to the limited database, most notably to bermudagrasss culture. The results bring attention to the multitude of factors that play a determinant role in the efficiency of use of fertilizer N and the attendant risk of NO3–N leaching losses in bermudagrass turf. These factors include fertilizer N source, N rate, N solubility, season of year, frequency of application, irrigation, growth stage, and stand vigor. One of the more salient lessons we illustrate is that high N applications at the end of the growing season (e.g., autumn), a widely used but controversial practice of warm-season turf managers in the southern USA (Goatley et al., 1998), clearly increases the risk of N losses by leaching.
Our findings imply a tradeoff between stand vigor and color and NO3–N leaching risk with the slow-release N products. That is, URE and SCU tend to enhance vigor and greening (through more rapid N availability and N uptake), but they also increase the risk of N loss. Conversely, the sparingly soluble HYD does not promote as much vigor and color but does seem to minimize the risk of N leaching loss at equivalent N application rates and frequencies. This type of N source may be highly beneficial from the view of abating potential NO3 contamination of ground water, because in our study, it did decrease or essentially eliminate the loss of NO3–N through the leaching fraction under more frequent application and reduced N demand periods (Fig. 3, Exp. 2).
In late fall (later stages of Exp. 2, late October through November), N yield was hardly affected by N source at a given N rate (Fig. 2). This means that a product such as HYD could be effective in improving fall N fertilization efficiency without a major sacrifice in vigor of the grass. Even under longer photoperiods more conductive to growth (Exp. 1), it appeared that higher HYD application rate and frequency overcame its lack of solubility so that N yield was not greatly reduced below that of SCU and URE.
For practical turfgrass management, high clipping growth rates increase maintenance costs. Therefore, turf quality becomes a major factor determining management practices. It appears that even with slowly soluble N sources (e.g., HYD), we may be able to achieve a proper balance between N application rate and frequency that provides satisfactory vigor and color while minimizing NO3 leaching loss potential. The use of highly soluble N sources in bermudagrass (e.g., URE) is still a viable practice, but at the end of the growing season, heavy irrigation with high N rates will result in a potential risk of NO3–N losses by leaching.
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ACKNOWLEDGMENTS |
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONSIGNIFICANCE AND APPLICABILITY...REFERENCES |
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This article has been cited by other articles:
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  Z. M. Easton and A. M. Petrovic Fertilizer Source Effect on Ground and Surface Water Quality in Drainage from Turfgrass J. Environ. Qual., March 1, 2004; 33(2): 645 - 655. [Abstract] [Full Text] [PDF]
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