Atmospheric deposition as an important nitrogen load to a typical agroecosystem in the Huang-Huai-Hai Plain. 1. Measurement and preliminary results

Atmospheric Environment 45 (2011) 3400e3405

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Atmospheric deposition as an important nitrogen load to a typical agroecosystem in the Huang-Huai-Hai Plain. 1. Measurement and preliminary results Ping Huang a, b, Jiabao Zhang a, *, Anning Zhu a, Xiuli Xin a, Congzhi Zhang a, b, Donghao Ma a a b

Fengqiu Agro-ecological Experimental Station, State Key Laboratory of Soil Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, PR China Graduate School of Chinese Academy of Sciences, Beijing 100049, PR China

a r t i c l e i n f o

a b s t r a c t

Article history: Received 4 August 2010 Received in revised form 19 March 2011 Accepted 23 March 2011

Atmospheric nitrogen (N) deposition has been widely considered as an important N input into agroecosystems, but its measurement involves considerable uncertainties with various methods. In this study, a field sampler with distilled water as a surrogate surface was developed and trialed for the collection of dry and wet N deposition. The direct measuring results were compared with the value calculated by the N mass balance method (crop N uptake from plots receiving no N fertilizers of the long-term fertilization experiment in the monitoring station). The results indicated that exposure durations of 3e5 days and water volumes of 2000e2800 ml were tested to be suitable to collect dry N deposition, while water volumes of less than 1000 ml and sampling conducted immediately after rain event were found to be appropriate for wet N collection under the present experimental conditions. The monitoring work was conducted from June 2008 to May 2009, and annual N deposition totaled up to 40.32 kg N ha
1, of which dry deposition accounted for 62.45%. NH4eN was the dominant species in N deposition and contributed 62.68% and 66.00% to wet and dry deposition, respectively. Organic N (O-N) was found to make greater contributions than NO3eN in both dry and wet depositions. Total N deposition was parallel to the results estimated by the method of mass N balance from the long-term experiment, as 45.6 kg N ha
1. These results provide helpful knowledge to elucidate the N deposition scenario of a typical agroecosystem and can be of great importance for the calculation of fertilizer recommendations in the Huang-Huai-Hai Plain. Ó 2011 Elsevier Ltd. All rights reserved.

Keywords: Atmospheric nitrogen (N) deposition Water surface sampler Agroecosystem Huang-Huai-Hai Plain

1. Introduction Atmospheric nitrogen (N) deposition has been found to have great impacts on various ecosystems, such as water bodies, forests and farmlands, and even slight increases in atmospheric N inputs could lead to considerable changes in them (Goulding et al., 1998; Matson et al., 1999; Baron et al., 2000). Increased N deposition was reported to accelerate the emission of methane and carbon dioxide (Aerts and de Caluwe, 1999), enhance nitrate leaching and parasite attacks (Allott et al., 1995; Yesmin et al., 1995; Fluckiger and Braun, 1998; Evans et al., 2008), and stimulate some chemical soil processes, such as acidification, nitrification, and mineralization of organic matter (Houdijk et al., 1993; Hagedorn et al., 2003; Xu et al., 2004; Scheuner and Makeschin, 2005). Huang-Huai-Hai Plain, producing one quarter of total grain yield in China, has witnessed decades’ rapid development and also * Corresponding author. Institute of Soil Science, Chinese Academy of Sciences, 71 East Beijing Road, Nanjing 210008, PR China. Tel.: þ86 25 8688 1228; fax: þ86 25 8688 1000. E-mail address: [email protected] (J. Zhang). 1352-2310/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2011.03.049

serious environmental problems, in the light of the current intensive agricultural practices (Cai et al., 2002; Hu et al., 2005). These human practices may have doubled N inputs into terrestrial ecosystems (Matson et al., 1999; Liu et al., 2010), but detailed information was not available in this area. Attempts have been made to measure and quantify atmospheric N deposition in the neighboring areas. Liu et al. (2006) and Zhang et al. (2006) investigated the wet and bulk N deposition in the North China Plain and found that atmospheric N deposition amounted to 30.6 kg N ha
1, and great differences between wet and bulk N deposition revealed that dry deposition would be an important atmospheric N source, but related information was not clear. Shen et al. (2009) reported that NH3, HNO3 and particulate NH4þ and NO3
were important components of dry deposition in the North China Plain; however, the results, without considering organic N (O-N) and wet classes, could lead to considerable underestimates of total (wet þ dry) N deposition (Krupa and Moncrief, 2002; Zhang et al., 2008; Liu et al., 2010). He et al. (2007) estimated total airborne N input, up to 83.3 kg N ha
1, in the North China Plain using 15N dilution method; however, the results could only estimate the gross amount of N deposition with

P. Huang et al. / Atmospheric Environment 45 (2011) 3400e3405

2. Methods and materials 2.1. Study site Fengqiu Agro-ecological Experimental Station (114 240 E, 35 000 N), Chinese Academy of Sciences, is located in the hinterland of the Huang-Huai-Hai Plain, with flat terrain and an average altitude of 67.5 m above sea level. This region has a typical monsoon climate with an average annual temperature of 13.9  C and average annual rainfall of approximately 615 mm. The method validation study was conducted at an experimental field (35 m width, 80 m length) from March to April in 2008, and the monitoring work was performed on the ground of the meteorological observatory field (immediately adjacent to the experimental field) from the beginning of June in 2008 to the end of May in 2009. Monthly average air temperature and cumulative precipitation during the calibration and monitoring period are provided in Fig. 1. The experimental station is about 130 km from Zhengzhou, the capital of Henan province, and more than 50 km from the nearest cities of Kaifeng and Xinxiang. No point sources of N pollution, such as large-sized grazing properties and heavy pollutant-emitting factories, are within 30 km of the station. Wheat-corn rotation is the prevailing cropping system in the study area, and crop stubble is pulverized and returned to farmlands instead of being burnt. When wheat and corn are sown in the middle of October and early June, respectively, basal fertilizers are simultaneously incorporated. Topdressings of N fertilizers are generally applied in early March and late July for wheat and corn, respectively, and the annual application rate of N fertilizers amounts to 500e700 kg N ha
1 (Zhu et al., 2005). 2.2. Method corroboration and sample collection To investigate the effect of water volume in the sampler (diameter ¼ 0.35 m, height ¼ 0.15 m) on deposition results, six

30

240

Precipitation (mm)

200

Precipitation Temperature

20

160 10 120 0 80

Temperature

-10

40 0

-20

08-03 08-04 08-05 08-06 08-07 08-08 08-09 08-10 08-11 08-12 09-01 09-02 09-03 09-04 09-05

detailed information missed. Therefore, additional reliable measurements of total atmospheric N deposition are urgently required to develop a better understanding of the N deposition scenarios. Rain gauges, wet-only precipitation samplers, bulk precipitation samplers, and active or passive auto-samplers were commonly used in the old investigations (Liu et al., 2006; Ayars and Gao, 2007; Chen and Mulder, 2007; Gao et al., 2007; Xie et al., 2008; Shen et al., 2009); however, respective uncertainties of these methods in measuring total atmospheric N deposition, especially for dry deposition, hampered the measuring and estimating results (Wesely and Hicks, 2000; Lohse et al., 2008). Samplers with distilled water as the surrogate surface have been tested to be effective in the collection of dry deposition of water-soluble gaseous or aerosol species and coarse and fine particles (Yi et al., 1997; Shahin et al., 2002; Raymond et al., 2004), but atmospheric N deposition should be collected comprehensively, including wet and dry classes, in order to minimize sampling uncertainties (Dämmgen et al., 2005). So whether the popular-used water surrogate method was applicable in the measurement of integrated wet and dry N deposition was unknown and needed to be tested as the deposited N components may convert or transform through chemical, physical or biological processes in the samplers during the collection process (Krupa and Moncrief, 2002; Chen and Mulder, 2007). The objectives of this work were to validate the sampling method for the collection of both dry and wet deposition, to monitor the monthly and annual atmospheric N deposition and elucidate the contributions of each component (NO3eN, NH4eN, and O-N) to total N deposition in the Huang-Huai-Hai Plain.

3401

Fig. 1. Monthly average air temperature and precipitation during the sampling period.

different volumes of distilled water, approximately 1000(V1), 1500(V2), 2000(V3), 2500(V4), 3100(V5), and 3800(V6) ml, were added to identical plastic samplers (rinsed three times with distilled water before use) for the collection of dry N deposition on the morning of March 24th, 2008. Each treatment had three replicates. These samplers were placed randomly on top of adjacent two plot walls (about 0.3 m above ground) of the experimental field. On the morning of March 27th, the volumes of water remaining in the samplers were measured using a 500 ml graduated flask after thorough agitation and mixing with a glass stick. Water samples (about 150 ml) were collected in clean plastic bottles (200 ml), sealed and stored at
2  C until analysis. No biocide was used for sample conservation because of limited conversion of O-N to mineral N under such conditions (Chen and Mulder, 2007). Similarly, six different volumes of distilled water, about 500(V7), 1200(V8), 2000(V9), 2500(V10), 3200(V11), and 3800(V12) ml, were added to the samplers on April 9th, 2008 for the collection of wet N deposition based on a forecast rain event. When the rain stopped, the volumes of water in the samplers were immediately measured and sampled using the procedures described above. Fifteen samplers each with about 2900 ml distilled water were placed on top of one plot walls of the field for dry-only deposition collection. Five sampling intervals (1, 3, 5, 7, and 9 days after placement, designated as T1, T2, T3, T4 and T5, respectively) were determined to investigate the effect of water exposure duration on the collection of dry N deposition. At each sampling time, three samplers were randomly selected to be investigated, using the sampling procedures described above. Based on the results of the validation study, a sampler was installed to monitor N deposition. The sampler was supported by a steel structure for 1.3 m above the ground to prevent contamination from surface soil and plants, and shielded by a stainless steel net (pore size, 0.02  0.02 m2) to avoid bird disturbance and crop stubble contamination. In hot seasons (JuneeOctober), dry deposition samples were collected at an interval of three days, while in other seasons, they were sampled at the intervals of three to five days if no rain intervened. Before each rain event predicted by the weather forecast, a dry deposition sample was collected following the abovementioned protocols, simultaneously, an identical sampler (rinsed with distilled water for three times before use) with a small amount of distilled water (usually less than 1000 ml) was placed to collect wet deposition. Immediately after each rain event,

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P. Huang et al. / Atmospheric Environment 45 (2011) 3400e3405

a water sample for wet deposition was collected; simultaneously, about 2500 ml distilled water was added to another clean sampler to collect dry deposition. When water in the sampler was frozen in cold seasons, samples were thawed at room temperature prior to sampling and another sampler was in service outside.

Table 1 Dry nitrogen deposition collected by different volumes of distilled water. Vr ¼ water volume remaining in the collectors, O-N ¼ organic nitrogen, T-N ¼ total nitrogen. Vi represents different adding volumes of distilled water, V1, V2, V3, V4, V5 and V6 indicate 1000 ml, 1500 ml, 2000 ml, 2500 ml, 3100 ml and 3800 ml, respectively. Treatment

NO3eN

Vr


1

ml

2.3. Sample analysis Water samples were analyzed within 2 months of storage. Before analysis, the frozen samples were first thawed at room temperature. Total N (T-N) was measured by the alkaline potassium peroxydisulfate oxidation method (APOM) (Nelson and Sommers, 1975; Cabrera and Beare, 1993). Prior to the analysis of T-N, water samples were shaken for 2 min to agitate the sunken particles at the bottom of these containers. After sampling for the analysis of T-N, water samples were filtered through filter papers (Xinxing No. 202, pore size 30 mm, GB/T1914-93, Hangzhou) for the analysis of NO3eN and NH4eN, which were determined by an ultraviolet spectrophotometer (UV1601, Shimadzu, Japan). The NO3
was directly calculated by the absorbance difference at the wavelengths of 220 and 275 nm, while NH4þ was measured by the indo-phenol-blue colorimetric method at a wavelength of 625 nm (Lu, 2000). 2.4. Data analysis Analysis of variance (one-way ANOVA) and least significant difference (LSD) calculations at P ¼ 0.05 were performed to identify statistically significant differences using the SPSS 15.0 software package for Windows. All figures were processed by Origin 8.0. Dry deposition (g N ha
1) of NO3eN, NH4eN, O-N and T-N was calculated by the following equations:

DNðdÞ ¼ CNðdÞ  Vd  1:039  10
4

(1)

DAðdÞ ¼ CAðdÞ  Vd  1:039  10
4

(2)

DTðdÞ ¼ CTðdÞ  Vd  1:039  10
4

(3)

DOðdÞ ¼ DTðdÞ
ðDNðdÞ þ DAðdÞÞ

(4)

where DN(d), DA(d), DT(d) and DO(d) respectively represent dry deposition of NO3eN, NH4eN, T-N and O-N during each sampling period; CN(d), CA(d), and CT(d) denote the concentrations of NO3eN, NH4eN, and T-N in the water sample, respectively; Vd represents the remaining water volume in the sampler at each sampling; and 1.039  10
4 is a constant calculated from the conversion of unit and area. Monthly or annual dry deposition (kg N ha
1) of NO3eN, NH4eN, O-N and T-N was obtained by summing the deposition amount at the required time scale (month or year). Wet deposition was calculated accordingly. 2.5. Estimation of N deposition from long-term experiment N deposition calculated from the N balance of long-term fertilization experiment was found to be effective in validating the direct measurements (Weigel et al., 2000; He et al., 2007), and N uptake by crops from the plots receiving no N fertilizers can be an important reference for N deposition. Such a long-term experiment (from 1989 to present), about 50 m north from the monitoring site, with a summer-corn and winter-wheat rotation system, was located in the station, and its detailed information was described in

V1 V2 V3 V4 V5 V6

833 1290 1823 2400 2960 3623

g ha (40) (30) (31) (26) (75) (45)

22.7 32.2 37.4 36.3 35.2 32.7

(1.2)a (1.0)b (0.2)c (0.2)cd (0.3)d (1.1)b

NH4eN g ha


1

53.5 67.6 76.7 74.9 73.9 57.9

(4.3)a (3.5)b (0.2)c (0.4)c (1.3)c (4.3)a

O-N

T-N
1

g ha 30.5 18.4 18.9 22.6 23.4 30.6

(9.8)a (5.4)b (0.7)b (1.2)ab (1.3)ab (6.3)a

g ha
1 106.7 118.2 133.0 133.7 132.4 121.2

(12.7)a (8.8)ab (0.6)c (1.1)c (1.7)c (8.1)bc

Numbers in the parentheses are standard deviations (n ¼ 3). Values followed by different letters are significantly different (P < 0.05).

Meng et al. (2005). The calculation of mass N balance referred to the protocol described in He et al. (2007). 3. Results and discussion 3.1. Measurement method validation Water volume in the sampler had a significant effect on the collection of NO3eN, NH4eN, O-N and T-N (Table 1). Dry N compounds, except for O-N, firstly increased with the increase in water volumes up to 2500 ml, and then decreased with more water addition. Heavy evaporation and concomitant N transformation or re-entry into the air may have been responsible for the relatively small amount of N sedimentation in the low water volumes (Yi et al., 1997; Krupa and Moncrief, 2002). While in the high volumes, dilution effect and consequent analysis deviation may explain the decrease in N absorption (Liu et al., 2006). Water volume demonstrated a small effect on the collection of wet N deposition under the tested gradients (Table 2). However, the variance increased when the absorbing water amount exceeded 2500 ml due to the dilution effect and measurement deviation, especially when little rainfall occurred. If heavy rain poured, high water volumes in samplers may have led to overflow and thus missing N from the measurement. Therefore, a water volume of 2000e2800 ml was considered to be appropriate for dry N collection, and less than 1000 ml for wet in this area. Sampling intervals were observed to have considerable influence on dry deposition collection (Table 3). O-N and NH4eN differed greatly with the sampling intervals, perhaps as a result of O-N transformation and ammonia equilibrium with the air. Daily sampling resulted in little N collection may be due to analysis deviation, and when sampling interval prolonged to one week or more, great O-N transformation and ammonia volatilization would

Table 2 Wet nitrogen deposition collected by different volumes of distilled water. Vr ¼ water volume remaining in the collectors, O-N ¼ organic nitrogen, T-N ¼ total nitrogen. Vi represents different adding volumes of distilled water, V7, V8, V9, V10, V11 and V12 denote 500 ml, 1200 ml, 2000 ml, 2500 ml, 3200 ml and 3800 ml, respectively. Treatment

V7 V8 V9 V10 V11 V12

Vr

NO3eN

NH4eN

O-N

T-N

ml

g ha
1

g ha
1

g ha
1

g ha
1

31.8 32.5 31.8 31.7 33.3 33.4

65.8 65.7 65.3 65.3 66.5 66.5

3.5 3.1 1.7 3.5 3.7 14.2

101.1 101.3 98.8 100.5 103.6 101.4

933 1673 2400 2940 3670 4263

(25) (32) (26) (36) (26) (42)

(0.9)a (0.4)a (0.5)a (0.5)a (1.2)a (2.6)a

(1.4)b (0.3)b (0.6)b (1.0)b (0.3)b (1.5)b

(0.6)c (0.4)c (0.7)c (0.6)c (3.4)c (0.9)c

(1.0)df (0.3)df (0.9)d (0.2)df (4.2)ef (3.7)df

Numbers in the parentheses are standard deviations (n ¼ 3). Values followed by different letters are significantly different (P < 0.05).

Values in the parentheses are standard deviations (n ¼ 3).

happen, which led to underestimates of N deposition. Therefore, if samples were exposed to open air and not taken within an appropriate time (3e5 days), the measuring results would be distorted. As spatial variation of N deposition was tested to be negligible in the current study (data not shown), comparable to the results within 1 km in Melle (Belgium) (Staelens et al., 2005), both wet and dry depositions were collected at a single site to represent the whole field situation. 3.2. Total N deposition during the monitoring period

Fig. 3. Temporal changes in the components of the atmospheric N deposition based on monthly calculations. The solid arrows represent the application of N fertilizer.

Natural N deposition has been considerably disturbed by anthropogenic activities, typically by agricultural practices, such as tillage and fertilizer application (Krupa and Moncrief, 2002; Liu et al., 2006; Xie et al., 2008). Croplands in the study area have been commonly tilled twice a year mainly in early June and middle October, while fertilizers (mostly urea and ammonium biphosphate) are split into four applications in early June, late July, middle October, and early March (Fig. 3). As fertilizer incorporated, particularly in the warm and humid seasons (Fig. 1), nitrogen losses through ammonia volatilization and oxides of nitrogen greatly increased (Cai et al., 2002; Zhang et al., 2004a,b), and thus the subsequent N deposition (Krupa and Moncrief, 2002). Dry N deposition was high in the cold and dry months, such as January and February (Figs. 1, 2 and 5), as well as in the hot seasons. Coarse particles (dust and sand) induced by strong wind from the nearly bare farmland may explain the large amount of dry deposition in these months. When crop canopy began to cover the surface of farmland in March, dry N deposition declined gradually (Fig. 3). However, Liu et al. (2006) reported that atmospheric deposition mainly existed from April to September, since the results gave little attention to dry deposition. 3.3. Composition dynamics of the total N deposition Deposited N components varied significantly with months (Figs. 3, 4 and 5); NH4eN primarily dominated the N species in both wet and dry deposition, agreed well with the published reports (Liu 2.5

Wet deposition (kg N ha-1 )

3

2

1

2

0

Dry Wet

4

NO3-N NH4-N O-N

2.0 1.5 1.0 0.5

09-05

09-04

09-03

09-02

09-01

08-12

08-11

08-10

08-09

08-08

08-07

09-05

09-04

09-03

09-02

09-01

08-12

08-11

08-10

08-09

08-08

08-07

Fig. 2. Monthly dynamics of the wet versus dry N deposition in the monitoring year.

08-06

0.0

0

08-06

Atmospheric N deposition (kg N ha -1)

Only when intensive rain occurred (JulyeSeptember) did wet deposition outweigh dry deposition (Figs. 1 and 2). During the whole monitoring year, annual N deposition amounted to 40.32 kg N ha
1, equal to about 8% of annual N application in this area, with dry deposition contributing 62.45% (25.18 kg N ha
1). In comparison to the total N deposition of 70.7 kg N ha
1 reported for a forest (Hu et al., 2007), the values for the agroecosystem were low, mainly due to higher N deposition velocity and lower surface resistance on forests (Zhang et al., 2004a,b). Liu et al. (2006) reported the bulk inorganic N deposition in Beijing area totaled up to 30.6 kg N ha
1, and Shen et al. (2009) measured the dry N deposition in the North China Plain up to 55 kg N ha
1, while Xie et al. (2008) estimated the wet-only N deposition as 27 kg N ha
1 in the Tai Lake region, which were much higher than the present study mainly due to their close vicinity to metropolitan cities and industrial zones (Krupa and Moncrief, 2002; Scheuner and Makeschin, 2005). In addition, He et al. (2007) quantified the total N deposition using 15N isotope dilution method, with a result of 83.3 kg N ha
1, which may be explained by the impact of neighboring heavy industries, or by the overestimate resulting from crop canopy spread out of the experimental pots.

4

09-05

(4.2) (0.9) (2.1) (3.2) (23.4)

09-04

38.1 144.2 239.8 338.1 293.4

09-03

g ha

0 (0) 12.9 (1.0) 17.6 (0.5) 19.9 (1.8) 16.8 (0.1)

09-02

g ha

09-01

(5.4) (1.0) (1.8) (5.8) (21.0)

08-12

26.4 90.5 153.5 252.5 222.9

08-11

(1.7) (0.2) (0.7) (3.6) (2.4)

6

08-10

11.8 40.8 68.7 65.7 53.7


1

08-09

(95) (35) (56) (40) (32)

T-N
1

g ha

g ha

2780 2577 2270 1887 1343

O-N


1

08-08

ml T1 T2 T3 T4 T5

NH4eN


1

O-N NH 4 -N NO3 -N

08-07

NO3eN

Vr

3403

8

08-06

Treatment

-1

Table 3 Dry nitrogen deposition collected at different time intervals. Vr ¼ water volume remaining in the collectors, O-N ¼ organic nitrogen, T-N ¼ total nitrogen. T1, T2, T3, T4 and T5 indicate different sampling intervals, as 1, 3, 5, 7, and 9 days, respectively.

Atmospheric deposition (kg N ha )

P. Huang et al. / Atmospheric Environment 45 (2011) 3400e3405

Fig. 4. Monthly dynamics of N components in wet deposition during the monitoring period.

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P. Huang et al. / Atmospheric Environment 45 (2011) 3400e3405

Dry deposition (kg N ha -1)

3.0 NO 3 -N NH 4 -N O-N

2.5 2.0 1.5 1.0 0.5

09-05

09-04

09-03

09-02

09-01

08-12

08-11

08-10

08-09

08-08

08-07

08-06

0.0

Fig. 5. Monthly dynamics of N components in dry deposition during the monitoring period.

et al., 2006; Xie et al., 2008), and exhibited great temporal variation, ranging from 0.44 (May) to 4.70 kg N ha
1 (August), while NO3eN varied slightly (0.24e0.98 kg N ha
1). Annual NH4eN, NO3eN, and O-N deposition amounted to 26.11, 6.13, and 8.08 kg N ha
1 (Fig. 3), respectively, accounting for 64.76%, 15.20%, and 20.04% of the total N deposition, respectively. Annual dry deposition of NH4eN, NO3eN, and O-N respectively accounted for 16.62 (66.00%), 3.34 (13.26%), and 5.22 (20.73%) kg N ha
1 of total dry N deposition (Fig. 5), and the proportion of inorganic N species was comparable to the results in the North China Plain (Shen et al., 2009). O-N deposition played an important role in total N deposition (Fig. 3), and its contribution even surpassed the NO3eN in both wet and dry depositions (Figs. 4 and 5). Therefore, if O-N were not incorporated in the measurement, total N deposition would be substantially underestimated (Lohse et al., 2008; Zhang et al., 2008).

responsible for the higher N deposition. Annual N deposition was estimated as 45.6 kg N ha
1 in 2009, largely similar to the value from direct measurement. If the small amount of N inputs by irrigation and biological fixation was included into the mass balance calculation, these results may be more parallel. In this investigation, preparation for dealing with rain events was based on weather forecast, which would lead to some uncertainties. If rain occurred late in the night or a slight rainfall occurred with no warning signs, the differentiation between dry and wet deposition was not maintained strictly as required by the experimental design, and only total N deposition could be obtained. In addition, the physical, biological, and chemical properties of water surface were totally different from that of the farmland; however, deposition velocities of major gaseous N compounds on water surface were generally similar to that on the farmland (Wesely and Hicks, 2000; Zhang et al., 2004a,b). So the results obtained with the water surrogate surface method could be a reference of actual value for atmospheric N deposition in the study area. On the basis of this work, an auto-sampler with proper conservation units, such as refrigerators following the aforementioned sampling protocols deserves being developed to replace the time-consuming manual work. Atmospheric N deposition has been found to be substantially influenced by some temporally varied meteorological elements, such as air temperature, relative humidity, and rainfall (Moncoulon et al., 2004; Chen and Mulder, 2007; Lohse et al., 2008). In addition, the archived measurement results for N deposition, especially for the dry classes, varied significantly with different sampling methods (Dämmgen et al., 2005; He et al., 2007). Therefore, interannual variations of N deposition and its correlations with these factors require further research, and various measuring techniques using for the dry deposition monitoring should be integrated to obtain reliable results in such intensively managed agroecosystems. 4. Conclusion

3.4. N deposition estimated by the mass N balance method

-1

Estimated annual N deposition (kg N ha )

N uptake by crops receiving no N fertilizers were calculated since 2001 (Fig. 6), and the values ranged from 40.5 to 61.5 kg N ha
1 during this period, which were consistent with the results from the Static Fertilization Experiment in Germany (Weigel et al., 2000), 50e58 kg N ha
1, but generally lower than analogous results reported by He et al. (2007) in Changping, as 62.2e115.7 kg N ha
1. Heavy industrial factories distributed in its adjacent areas would be 60

45

30

15

0

2001

2002 2003 2004 2005 2006 2007 2008 2009

Fig. 6. Estimated N deposition by the mass balance method from the long-term fertilization experiment in the Fengqiu Agro-ecological Experimental Station. Error bars refer to the standard deviation of crop (summer corn and winter wheat) N uptake (n ¼ 4).

Distilled water-based method used in this study was tested to be reliable for the measurement of atmospheric N deposition by comparison to the estimated value (N uptake by crops from plots receiving no N fertilizers) from long-term experiment. Appropriate conditions for dry N collection should be confined with a sampling interval of 3e5 days and a water volume of 2000e2800 ml in the current experimental design. While less than 1000 ml and sampling immediately after rain stopped would be appropriate for wet N collection. Within a whole observation year (from June 2008 to May 2009), atmospheric N deposition totaled 40.32 kg N ha
1, a significant load to the agroecosystem in the Huang-Huai-Hai Plain, of which dry deposition contributed more than 60%. NH4eN was the dominant N species in both wet and dry deposition, and accounted for nearly 65% of total N deposition. O-N accounted for a considerable portion of the N deposition, representing 18.89% and 20.73% in wet and dry deposition, respectively, which was higher than the results for NO3eN. These results provide valuable reference information for understandings of N deposition scenarios and calculations of N balance and fertilization in this area. If this type of N input was taken into account in fertilizer recommendations in agricultural practices, a great decrease in N application rates and losses can be achieved, which, in turn, could induce a decrease in atmospheric N deposition. Acknowledgements This study was funded by the National Basic Research Program of China (Project No. 2011CB100506) and the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KSCX1-YW-09-05, KSCX2-EW-N-08). The authors would like to

P. Huang et al. / Atmospheric Environment 45 (2011) 3400e3405

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