- Email: [email protected]
Denitrification Losses and N2O Emissions from Nitrogen Fertilizer Applied to a Vegetable Field1
Pedosphere 16(3): 390-397, 2006 ISSN 1002-0160/CN 32-1315/P @ 2006 Soil Science Society of China Published by Elsevier Limited and Science Press
Denitrification Losses and N2O Emissions from Nitrogen Fertilizer Applied to a Vegetable Field*' CAO Bing',233, He Fa-Yun', Xu Qiu-Ming3, Yin Bin' and CAI Gui-Xin't*2 'State Key laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 810008 (China). Email: caobingObaafs.net.cn Graduate School of the Chinese Academy of Sciences, Beijing 100039 (China) 31nstitute of Plant Nutrition and Resources, Bezjing Academy of Agricultural and Forestry Sciences, Beijing 100089 (China) (Received December 12, 2005; revised February 17, 2006)
ABSTRACT A field experiment was conducted on Chinese cabbage (Brassica campestris L. ssp. pekinensis (Lour.) Olsson) in a Nanjing suburb in 2003. The experiment included 4 treatments in a randomized complete block design with 3 replicates: zero chemical fertilizer N (CK); urea at rates of 300 kg N ha-' (U300) and 600 kg N ha-' (USOO), both as basal and two topdressings; and polymer-coated urea at a rate of 180 kg N hap1 (PCU180) as a basal application. The acetylene inhibition technique was used to measure denitrification (N2 N20) from intact soil cores and N 2 0 emissions in the absence of acetylene. Results showed that compared to CK total denitrification losses were significantly greater ( P 5 0.05) in the PCU180, U300, and U600 treatments, while NzO emissions in the U300 and U600 treatments were significantly higher ( P 5 0.05) than CK. In the U300 and U600 treatments peaks of denitrification and NzO emission were usually observed after N application. In the polymer-coated urea treatment (PCU180) during the period 20 to 40 days after transplanting, higher denitrification rates and N z 0 fluxes occurred. Compared with urea, polymer-coated urea did not show any effect on reducing denitrification losses and NzO emissions in terms of percentage of applied N. As temperature gradually decreased from transplanting to harvest, denitrification rates and N z 0 emissions tended to decrease. A significant ( P 5 0.01) positive correlation occurred between denitrification ( r = 0.872) or NzO emission ( r = 0.781) flux densities and soil temperature in the CK treatment with a stable nitrate content during the whole growing season.
+
Key Words:
denitrification loss, N z 0 emission, polymer-coated urea, urea, vegetable field
Nitrogen fertilization is crucial for achieving high yields in field vegetables (Li et al., 2000; Sun et al., 2003). Unfortunately, because they cause severe environmental problems, such as nitrate leaching, nitrous oxide (N2 0) emissions, and ammonia volatilization, many current intensive systems of vegetable production are not sustainable (Neeteson and Carton, 2001; Li et al., 2003). For example, in an irrigated vegetable field 14%-52% of the N input was found to be lost through denitrification (Ryden and Lund, 1980). Also, Tei et al. (1999) reported that significant quantities of miheral nitrogen were left in the soil after vegetable harvest, leading to potential risk of N leaching. Nevertheless, in order to obtain high yields, growers usually apply large amounts of N fertilizer. A survey in a Beijing suburb showed that farmers' N application rates for vegetables were over twice recommended rate, and the average residual soil mineral nitrogen content within 1 m depth was 412 kg N ha-', which was susceptible to nitrate leaching and denitrification (Li et al., 2000). Another survey in Shandong Province showed that in comparison with normal vegetable fields, N application rates were much higher and nitrogen loss was more serious in protected vegetable fields (Li et al., 2000). In the soil-plant system nitrification and denitrification are two important nitrogen transformation processes, both of which can produce NzO. Nitrous oxide is not .only one of the greenhouse gases contributing to global warming, but it also directly destroys the stratospheric ozone layer. Many factors *'Project supported by the National Natural Science Foundation of China (No. 40171048) and the Science and Technique Key Project of the Tenth Five-Year Plan of China (No. 2002BA516A03). *2Corresponding author. Email: [email protected].
DENITRIFICATION AND N20 EMISSIONS
39 1
affect denitrification loss and N2O emission, such as temperature, soil moisture, available C and N, as well as rate and type of N fertilizer (Eichner, 1990; Granli and Bockman, 1994; Su et al., 2005). About 70% of all anthropogenic N 2 0 emissions are from agriculture activity (Delgado and Mosier, 1996) with chemical nitrogen fertilization being considered the dominant source for N 2 0 emissions from agricultural soils. The intensity of the processes causing N20 emissions from cultivated soils is closely linked to fertilization rates (Mosier and Kroeze, 2000; Kaiser et aZ., 1998). To date, some research in China has been conducted on denitrification and N 2 0 emissions from cereal fields (Ding et al., 2001; Zhang et al., 2001; Zhang et al., 2004; Zou et al., 2002; Xiong et al., 2003), but little has been done with vegetable fields. One possible way to improve nitrogen use efficiency and to reduce environmental hazards is the use of controlled-release fertilizers (Shoji, 1999; Shaviv, 2001). The effectiveness of a fertilizer mainly depends on the extent t o which N supply matches plant demand (Shaviv, 2001). Controlled-release fertilizers have advantages, such as saving labor (only a single basal application within the whole plant growth period is needed), improving N use efficiency thereby allowing for a reduction of fertilizer application rate, decreasing NO, leaching as well as NzO and NO emissions, and maintaining high crop yields with good quality (Shoji and Kanno, 1994; Watanabe et al., 1999; Kosuge et al., 2001; Shoji et al., 2001; Cheng et al., 2002; Zheng et al., 2004). Recently, there has been an increase in studies on the effects of controlled-release fertilizers on crop growth and environmental problems in upland fields (Kosuge et al., 2001). The present study aimed to measure differences in denitrification losses and NzO emissions as well as mineral nitrogen (NHi-N and NOT-N) among a control, urea, and polymer-coated urea applied to a Chinese cabbage (Brassica campestris L. ssp. pekinensis (Lour.) Olsson) field. MATERIALS AND METHODS
Field experiment The experiment was carried out on a vegetable field of the Dongyang Scientific and Technical Station in the eastern suburb of Nanjing, Jiangsu Province, China, in 2003. The soil was an Agric Ferri-udic Argosol (Cooperative Research Group on Chinese Soil Taxonomy, 2001), with (in 0-20 cm) a pH (HZO) of 7.69, organic matter of 25.3 g kg-', total N of 1.52 g kg-', total P of 2.75 g kg-', total K of 22.9 g kg-', available P (Olsen P) of 48.0 mg kg-', and available K of 135 mg kg-'. The soil bulk density was 1.40 g ~ m - ~ . In this experiment, 4 treatments were included: a control (without chemical N fertilizer) (CK), a conventional nitrogen application rate of 600 kg N ha-' as urea (USOO), a reduced N application rate of 300 kg N ha-' as urea (U300), and a polymer-coated urea at a rate of 180 kg N ha-' (PCU180). Treatments were laid out in a randomized complete block design with three blocks, and the area of each plot was 25 m2 (5.0 m x 5.0 m). In addition, before transplanting seedlings 30 t pig manure ha-' with 11 g kg-l nitrogen content, 150 kg P205 ha-' as calcium monophosphate, and 150 kg K2O ha-' as potassium chloride were applied t o each plot. The manure, P, and K fertilizers as well as the urea (except for polymer-coated urea) were broadcasted on the soil surface and then plowed and harrowed. Polymer-coated urea (manufactured by the Institute of Plant Nutrition and Resources, Beijing Academy of Agricultural and Forestry Sciences) was applied as a band below the seedling in a single basal application as suggested by Shoji e t al. (2001) and Cheng et al. (2002). For the U300 and U600 treatments, urea was applied 3 times including one basal application with 25% of the total applied N and two topdressings with 25% on the 26th day and 50% on the 50th day after transplanting. For N topdressing, urea was broadcasted and immediately followed by irrigation of about 150 m3 ha-l with the same amounts of water being applied to the CK and PCU180 treatments. On September 4 following basal dressing, Chinese cabbage seedlings were transplanted with a density of 40 cm x 50 cm. The crop was irrigated daily during the first 4 days after transplanting and harvested on December 6, 2003.
392
B. CAO
et al.
Measurements and data analyses To measure the release of polymer-coated urea under field conditions five grams of polymer-coated urea was enclosed in a total of 18 plastic, about 1 mm mesh, net bags and buried during transplanting at a 10 cm soil depth. Three bags were retrieved on days 3, 7, 19, 30, 41, and 5 2 after transplanting. The remaining urea N in the bag was measured by the colorimetric method (Yamasoe, 1976), and then released urea N was calculated by subtracting the remaining urea N from total N. Denitrification losses were measured using the intact soil core-acetylene (C2H2) inhibition technique (Ryden et al., 1987). In the presence of C2H2, the reduction of N 2 0 to N2 gas was inhibited, so the denitrification loss was calculated from N20-N production. In the absence of C2H2, the N 2 0 production alone was used as an estimate of NzO emission. The soil core sampler (32 mm diameter and 150 mm deep) and the gas-tight PVC incubator (150 mm diameter by 150 mm deep) were the same as described by Cai et al. (2002). Duplicate sets of 8 soil cores were taken from each block and placed into incubators for all the treatments. The 8 soil cores were randomly taken in the CK, U300, and U600 treatments, while in the PCU180 treatment 4 soil cores were sampled close to the fertilizer band and the other 4 soil cores were taken from the middle of two rows. Each incubator lid was fitted with a rubber stopper for C2H2 amendment and gas sampling. After the lid was closed, about 500 mL of air was withdrawn from the incubator followed by addition of 180 mL of purified C2Hz (about 10% (v/v) CzH2 in the headspace). Thereafter, air was added to adjust to normal pressure. To maintain the same temperature and avoid complications due to diurnal temperature fluctuations, the incubators were kept for 24 h in a hole at the same depth adjacent to the experimental plots and covered with a thin layer of soil. After 24 h, a 20-mL gas sample was taken and transferred to an 18-mL gas-tight glass bottle. A subsample was analyzed for N 2 0 using an Agilent 4890D gas chromatograph equipped with a Poropak-Q packed column and an electron capture detector (ECD). The Poropak-Q was connected in series through a computer-controlled 6-valve system to backflush any volatile fluoride and chloride compounds. The flow rate was 30 cm3 min-l. Column and detector temperatures were 55 and 330 "C, respectively. After gas sampling, the soil samples were taken from the incubators without C2H2 for mineral N and soil water content analyses. Field moisture soil samples were extracted by shaking with 2 mol L-' KC1 solution (1:5 soil-solution ratio) for 1 h followed by filtration. The extracts were analyzed for NH,f-N and NO,-N using steam-distillation procedures. Gravimetric soil water content (oven-dried at 105 "C) was measured and water-filled pore space (WFPS) was calculated (Granli and Berckman, 1994). All measurements commenced 1 day after basal dressing and lasted for 93 days, which was just before harvest. Samples were taken around every 2-3 days after each N application and then at longer intervals. There were a total of 13 sampling times with 3 replicates at each sampling time. N2O loss during intervals between 2 sampling times was calculated as the average of the 2 measurements. In addition, the soil temperature at a depth of 7.5 cm was measured. Denitrification losses and N 2 0 emission fluxes for the four treatments measured throughout the Chinese cabbage growing season were compared. Also differences in means of NH,f-N and NO,-N for the four treatments were compared. A correlation analysis for denitrification or N2O emission flux densities and soil temperature was utilized. Statistical significance of total denitrification losses and N 2 0 emissions from the four different treatments was determined with ANOVA and mean separation using least significant difference (LSD) with P 5 0.05. RESULTS AND DISCUSSION
Mineral nitrogen During the Chinese cabbage growing season, application of chemical N fertilizer generally increased mineral N content in the soil (Fig. 1). In the CK treatment (without chemical N fertilizer), soil min-
DENITRIFICATION AND N2O EMISSIONS
393
era1 N, the sum of NH:-N and NOT-N, was low, being less than 8 mg kg-'. For the U300 and U600 treatments, peaks of NHl-N and NO,-N occurred shortly after N application with higher peaks in the U600 treatment, except for the first topdressing on day 26 with delayed sampling due to consecutive days of rainfall after the fertilization. The highest peaks of NHi-N and NO,-N occurred after the second topdressing (50% of the total applied N on day 50). NHl-N in the soil decreased quickly from its maximum value, while NO,-N decreased relatively slowly, especially after the second N topdressing where NOT-N of the U600 treatment remained at high levels (52 mg kg-') until the end of the experiment (Fig. 1). This phenomenon could partly be explained by the weak N uptake of the crop (personal communication). 100
-e C K
h
80
7
m
+ PCU180
Y
-
60
2
40
E
-c U300
-
100 8o
x
60 v
I
z
-
40
z
20
2
t
0
20
0
0 20
100
40 60 80 Days after transplanting
0
20
0
40
60
80
100
Days after transplanting
Fig. 1 Mineral nitrogen contents (means f SD) in 0-15 cm soil during the growing season of a Chinese cabbage field: NHZ-N (a) and NO,-N (b). The arrows at day 26 and day 50 indicate time of topdressing of urea at a conventional nitrogen application rate of 600 kg N hav1 (USOO), urea a t a reduced N application rate of 300 kg N hap1 (U300), and polymer-coated urea at 180 kg N ha-' (PCU180) with a control without chemical N fertilizer (CK).
Additionally, during the first 10 days after transplanting mineral N content of the PCU180 treatment was comparable to that of CK (Fig. 1). By the 20th day after transplanting, however, NH,f-N and NO;N in the PCU180 treatment increased to 10.3 mg kg-' and 30.1 mg kg-', respectively, which was the highest among the four treatments. The high level lasted for around 20 days and then decreased. The mineral N pattern of the PCU180 treatment was in accordance with the pattern of release rate of the polymer-coated urea (Fig. 2). 4 r I
-c'n X
3 -
4C K
3
--c U300
2
-x-
PCU180
27
+-a
g.c
sz zo, ' E Z 1
ill% -
zs
20
a,
n
3-
0
0
I
0
15
30
45
Days after transplanting Fig. 2
U600
60
0 0
20 40 60 80 Days after transplanting
100
Cumulative nitrogen released (means f SD) from polymer-coated urea during the Chinese cabbage growing season.
Fig. 3 Denitrification flux from different treatments during the growing season of a Chinese cabbage field. The arrows at day 26 and day 50 indicate time of topdressing of urea at a conventional nitrogen application rate of 600 kg N ha-' (USOO), urea at a reduced N application rate of 300 kg N ha-' (U300), and polymer-coated urea at 180 kg N hap1 (PCU180) with a control without chemical N fertilizer (CK).
Denitrification loss and
N2 0
emission
Denitrification and NzO fluxes during the Chinese cabbage growing season are shown in Figs. 3 and
B. CAO et at.
394
4, respectively. In general, denitrification and N 2 0 fluxes in the CK treatment (with pig manure, but without chemical N fertilizer) were lower than those of the other three treatments with chemical N fertilizer additions (PCU180, U300 and U600). Except for the PCU180 treatment, maximum denitrification and N2O fluxes were observed on the 3rd day after transplanting (basal dressing).
-t
CK
-m-
U300 PCU180
-A-
n
E 10 0
0
20
40
60
80
Days after transplanting
100
-
80
+Temperature n
'
~
~
~
~
3 6 11 2 2 3 6 4 2 4 9 5 4 5 7 6 3 7 3 8 4 9 3
Days after transplanting
Fig. 4 NzO emission flux from different treatments during the growing season of a Chinese cabbage field. The arrows at day 26 and day 50 indicate time of topdressing of urea at a conventional nitrogen application rate of 600 kg N ha-' (USOO), urea at a reduced N application rate of 300 kg N ha-l (U300), and polymer-coated urea a t 180 kg N hap1 (PCU180) with a control without chemical N fertilizer (CK). Fig. 5 Soil temperature ("C) and water content (% water-filled pore space (WFPS)) during the growing season in a Chinese cabbage field.
The maximum denitrification and N 2 0 emission flux densities in CK were 1.68 and 0.08 kg N ha-' d-' , respectively. However, application of urea greatly promoted both denitrification and NzO production with the maximum denitrification rate and N 2 0 flux of the U300 treatment reaching 3.14 and 0.51 kg N ha-' d-', respectively, and the U600 treatment being 3.63 and 1.05 kg N ha-' d-l, correspondingly. Other researchers have also found that a combination of manure with chemical N fertilizer, in comparison to pig slurry alone, significantly increased denitrification and N 2 0 rates shortly after application (Arcara et al., 1999; Yang et al., 2003). For the U300 and U600 treatments, denitrification and N2O emission peaks were also observed after N fertilization except for N2O emission of the U300 treatment after the first urea topdressing (Figs. 3 and 4). Consecutive days of rainfall instantly after the first topdressing for the U300 and U600 treatments made the field too muddy to take soil core samples; consequently possible peaks of mineral N, denitrification and NzO emissions were missed (Figs. 1, 3 and 4). Denitrification and N 2 0 emission peaks for the three chemical N fertilizer treatments (PCU180, U300, and U600) were in accordance with peaks of NH,f-N and NOT-N (Figs. 1, 3 and 4). Figs. 3 and 4 also showed that during the period of 20 to 40 days after transplanting in the polymer-coated urea treatment (PCU180) denitrification rates were higher than those of the other three treatments and N2O fluxes were higher than the CK and U300 treatments. This was because of the higher soil mineral N during this period as shown by the N H l - N and NO,-N levels after transplanting (Fig. 1). Soil moisture of 0-15 cm ranged from 55.4% to 63.3% WFPS during the Chinese cabbage growing season (Fig. 5), which was favorable for denitrification and N 2 0 production (Klemedtsson et aL, 1988). However, soil temperature decreased greatly from about 32 "C at transplanting to about 5 "C at harvest (Fig. 5), which markedly influenced denitrification and N 2 0 emission. The time course of denitrification (Fig. 3) and N 2 0 emissions (Fig. 4) was similar to that of the temperature (Fig. 5) with the highest rates shortly after transplanting and decreasing to very low levels before harvest. 92%-95% of the denitrification losses and 65%-85% of N 2 0 emissions in the 4 treatments occurred before the second topdressing event (data not shown). A significant ( P 5 0.01) positive correlation was shown between denitrification ( T = 0.872) or N 2 0
~
m
DENITRIFICATION AND N2O EMISSIONS
395
emission ( r = 0.781) flux densities and soil temperature for the CK treatment with a stable NO,-N content during Chinese cabbage growing season (Fig. l b ) . The correlation was not shown for the other N fertilized treatments with variable NO,-N contents, which greatly affect the flux densities. Furthermore, when soil temperature dropped below 10 "C after 70 days (Fig.5), denitrification and NzO fluxes for the 4 treatments were very low despite high NO,-N in the U300 and U600 treatments (Fig. lb). This finding indicated that soil temperature was a primary regulator of nitrification-denitrification processes. Temperature markedly affects microorganism activity including that of nitrifiers and denitrifiers. When soil temperature is below 10 "C, denitrification and N2O emissions are barely detectable even though other conditions are favorable (Cho et al., 1975; Aulakh et al., 2001). Table I shows that chemical N fertilization significantly ( P 5 0.05) enhanced total denitrification losses and, except for the PCU180 treatment, N2O emissions. Total NzO emissions derived from chemical N fertilizer ranged from 1.09%-1.63% of applied N, which was similar to the value of 1.25% i 1% frequently used to estimate N 2 0 emissions from N fertilization (Bouwman, 1994). Total denitrification losses derived from chemical N fertilizer ranged from 4.33% to 8.55% of N applied, which was in the range of other reports of direct denitrification loss obtained from vegetable fields (Ryden and Lund, 1980; Bertelsen and Jensen, 1992), but higher than the results of upland cereal crops in China with similar incubation procedures (Zhang et al., 2001, Zhang et al., 2004; Ding et al., 2001; Zou et al., 2002). TABLE I Total denitrification losses and N20 emissions from different treatments during the growing season in a Chinese cabbage field Treatmenta)
Denitrification loss Amount
CK PCU180 U300 U600
Difference
__ kg N ha-' __ 19.8 ab) 35.2 b 15.4 40.1 b 20.3 45.8 b 26.0
N20 emission Percent of applied N
Amount
%
- k g N ha-'
8.55 6.76 4.33
1.77 a 4.71 ab 5.03 b 11.10 c
Difference
2.94 3.26 9.30
__
Percent of applied N
% 1.63 1.09 1.55
~
a)CK--control (without chemical N fertilizer); U6OO-urea at 600 kg N ha-l, a conventional nitrogen application rate; U300-urea at 300 kg N ha-l, a reduced N application rate; and PCU180-polymer-coated urea at 180 kg N ha-'. b)Values within each column followed by the same letter do not differ significantly ( P 5 0.05) using an LSD test.
Compared with other reports which identified the positive effects of controlled-release fertilizers on reduction of denitrification and NzO emissions (Shoji and Kanno, 1994; Shoji et al., 2001; Cheng et al., 2002; Zheng et al., 2004; Minami, 2005), polymer-coated urea compared to urea did not show any effect on reducing denitrification losses or N20 emissions in terms of percentage of applied N in this experiment (Table I). The possible reason was an oversupply of N from the polymer-coated urea resulting in high soil mineral N in the first half of the growing season (Fig. 1),and consequently high denitrification losses and N20 emissions occurred (Figs. 3 and 4). Generally, if the release dynamics of a controlled-release N fertilizer do not match the pattern of N uptake by the plant, the effectiveness of the fertilizer will be reduced and N loss will be increased due to an over-supply N during the period of plant growth or "tailing" effect after harvest (Shaviv, 2001). This was particularly important for upland crops because extreme water and temperature conditions frequently occurred, which markedly influenced the release rate and release period of these controlled-release fertilizers (Takahashi, 1998). ACKNOWLEDGEMENTS We would like t o express many thanks to Dr. Marco Roeckle, Technical University Carolo-Wilhelmina, Braunschweig, Germany, for his comments.
396
B. CAO et al.
REFERENCES Arcara, P. G., Gamba, C., Bidini, D. and Marchetti, R. 1999. The effect of urea and pig slurry fertilization on denitrification, direct nitrous oxide emission, volatile fatty acids, water-soluble carbon and anthrone-reactive carbon in maize-cropped soil from the Po plain (Modena, Italy). Biol. Fertil. Soils. 2 9 (3): 270-276. Aulakh, M. S., Khera, T . S. and Doran, J. W. 2001. Denitrification, N 2 0 and C02 fluxes in rice-wheat cropping system as affected by crop residues, fertilizer N and legume green manure. Biol. Fertil. Soils. 34: 375-389. Bertelsen, F. and Jensen, E. S. 1992. Gaseous nitrogen losses from field plots grown with pea or spring barley estimated by 15N mass balance and acetylene inhibition techniques. Plant Soil. 142: 287-295. Bouwman, A. F. 1994. Method to Estimated Direct Nitrous Oxide Emissions from Agricultural Soils. Report 773004004. National Institute of Public Health and Environmental Protection, Bilthoven. Cai, G. X., Chen, D. L., White, R. E., Fan, X. H., Pacholski, A., Zhu, Z. L. and Ding, H. 2002. Gaseous nitrogen losses from urea applied to maize on a calcareous fluveaquic soil in the North China Plain. Aust. J . Soil Res. 40: 737-748. Cheng, W., Nakajima, Y . , Sudo, S., Akiyama, H. and Tsuruta, H. 2002. N20 and NO emissions from a field of Chinese cabbage as influenced by band application of urea or controlled-release fertilizers. Nutrient Cycling in Agroecosystems. 63: 231-238. Cho, C. M., Sakdinan, L. and Chang, C. 1975. Denitrification intensity and capacity of three irrigated Alberta soils. Soil Sci. SOC. Am. J . 43: 945-950. Cooperative Research Group on Chinese Soil Taxonomy. 2001. Chinese Soil Taxonomy. Science Press, Beijing. 203pp. Delgado, J . A. and Mosier, A. R. 1996. Mitigation alternatives to decrease nitrous oxides emissions and urea-nitrogen loss and their effect on methane flux. J . Enwiron. Qual. 25: 1105-1 111. Ding, H., Cai, G. X., Wang, Y. S. and Chen, D. L. 2001. Nitrification-denitrification losses of nitrogen fertilizer and N 2 0 emission from maize-chao soil system in North China Plain. Scientia Agricultura Sinica (in Chinese). 34(4): 416-421. Eichner, M. J . 1990. Nitrous oxide emissions from fertilized soils: Summary of available data. J . Enwiron. Qzlal. 19: 2 72-2 80. Granli, T . and B@ckman,0. C. 1994. Nitrous oxide from agriculture. Norwegian Journal of Agricultural Sciences. (Supplementl2): 7-128. Kaiser, E. A., Kohrs, K., Kucke, M., Schnug, E., Munch, J. C. and Heinemeyer, 0. 1998. Nitrous oxide release from cultivated soils: Influence of different N-fertilizer type. Biol. F e d . Soils. 28: 36-43. Klemedtsson, L., Svensson, B. H. and Rosswall, T. 1988. Relationships between soil moisture content and nitrous oxide production during nitrification and denitrification. Biol. Fertil. Soils. 6: 106-111. Kosuge, S., Higashi, T. and Saigusa, M. 2001. Effect of controlled availability fertilizers on tomato cultivation by single basal application. Jpn. J. Soil Sci. Plant Nutr. (in Japanese). 72(5): 621-625. Li, X. L., Zhang, F. S. and Mi, G. H. 2000. Fertilizing for Sustainable Production of High Quality Vegetables (in Chinese). China Agricultural University Press, Beijing. 443pp. Li, J. L., Chen, X. P., Li, X. L. and Zhang, F. S. 2003. Effect of N fertilization on yield, nitrate content and N apparent losses of Chinese Cabbage. Acta Pedologica Sinica (in Chinese). 40(2): 261-266. Minami, K . 2005. N cycle, N flow trends in Japan, and strategies'for reducing NzO emission and NO, pollution. Pedosphere. 15(2): 164-172. Mosier, A. and Kroeze, C. 2000. Potential impact on the global atmospheric NzO budget of the increased nitrogen input required to meet future global food demands. Chemosphere: Global Change Sci. 2: 465-473. Neeteson, J. J. and Carton, 0. T. 2001. The environmental impact of nitrogen in field vegetable production. Acta Hort. 563: 21-28. Ryden, J. C. and Lund, L. J. 1980. Nature and extent of directly measured denitrification loss from some irrigated vegetable crop production units. Soil Sci. SOC.Am. J . 40: 505-511. Ryden, J. C . , Skinner, J. H. and Nixon, D. J. 1987. Soil core incubation system for the field measurement of denitrification using acetylene-inhibition. Soil Biol. Biochem. 19: 753-757 Shaviv, A. 2001. Advances in controlled-release fertilizers. Advances in Agronomy. 71: 1-49. Shoji, S. 1999. Meister Controlled Release Fertilizers-Properties and Utilization. Konno Printing Co., Ltd., Sendai. 160pp. Shoji, S. and Kanno, H. 1994. Use of polyolefin-coated fertilizers for increasing fertilizer efficiency and reducing nitrate leaching and nitrous oxide emissions. Fed. Res. 39: 147-152. Shoji, S., Delgado, J., Mosier, A. and Miura, Y . 2001. Use of controlled release fertilizers and nitrification inhibitors to increase nitrogen use efficiency and to conserve air and water quality. Commun. Soil Sci. Plant Anal. 32(7&8): 1051-1 070. Su, C. G., Yin, B., Zhu, Z. L. and Shen, Q. R. 2005. Gaseous loss of nitrogen from fields and wet deposition of atmospheric nitrogen and their environmental effects. Soils (in Chinese). 37(2): 113-120. Sun, Q., Ding, F. R., Li, P., Lu, H. X., Hu, X. and Liu, Z. J. 2003. Influence of nitrogen on nitrate accumulation in cabbage and N fertilizer application rate. Soils (in Chinese). 35(3): 255-258. Takahashi, M. 1998. Innovation of fertilizer application by using controlled-release fertilizers. 5. Application of fertilizer in vegetable planting (2). J p n . J . Soil Sci. Plant Nutr. (in Japanese). 69(3): 303-309.
DENITRIFICATION AND N 2 0 EMISSIONS
397
Tei, F., Benincasa, P. and Guiduci, M. 1999. Nitrogen fertilization of lettuce, processing tomato and sweet pepper: Yield, nitrogen uptake and the risk of nitrate leaching. Acta Hort. 506: 61-67. Watanabe, T., Ishikawa, T. and Minami, K. 1999. Mitigation of nitrous oxide emission by controlled availability fertilizer and nitrification inhibitor. Jpn. J. .Soil Sci. Plant Nutr. (in Japanese). 70(6): 747-753. Xiong, Z. Q., Xing, G. X., Tsuruta, H., Shi, S. L., Shen, G. Y. and Du, L. J. 2003. Nitrous oxide emissions from paddy soils as affected by incorporation of leguminous green manure and fertilization during double-cropping rice-growing season. Acta Pedologica Sznica (in Chinese). 40(5): 704-710. Yamasoe, B. 1976. Fertilizer Analysis Method (in Japanese). Yokanto Co., Ltd., Tokyo. pp. 60-67. Yang, X. M., Drury, C. F., Reynolds, W. D., Tan, C. S. and Mckenney, D. J. 2003. Interactive effects of composts and liquid pig manure with added nitrate on soil carbon dioxide and nitrous oxide emissions from soil under aerobic and anaerobic conditions. Can. J . Soil Sci. 83(4): 343-352. Zhang, Y. M., Chen, D. L., Zhang, J. B., Edis, R., Hu, C. S. and Zhu, A. N. 2004. Ammonia volatilization and denitrification losses from an irrigated maize-wheat rotation field in the North China Plain. Pedosphere. 14(4): 533-540. Zhang, Y. M., Dong, W. X., Zeng, J. H. and Chen, D. L. 2001. Dynamics of denitrification and N20 flux in maize field. Chinese Journal of Eco-Agriculture (in Chinese). 9(4): 70-72. Zheng, S. X., Liu, D. L., Nie, J., Dai, P. A. and Xiao, J. 2004. Fate and recovery efficiency of controlled release nitrogen fertilizer in flooding paddy soil. Plant Nutrition and Fertilizer Science (in Chinese), lO(2): 137-142. Zou, G. Y., Zhang, F. S. and Li, X. H. 2002. Study on nitrification-denitrificationof soil nitrogen in summer maize season. AgriculturaZ Research in the Arid Areas (in Chinese). 20(1): 30-34.
Denitrification Losses and N2O Emissions from Nitrogen Fertilizer Applied to a Vegetable Field*' CAO Bing',233, He Fa-Yun', Xu Qiu-Ming3, Yin Bin' and CAI Gui-Xin't*2 'State Key laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 810008 (China). Email: caobingObaafs.net.cn Graduate School of the Chinese Academy of Sciences, Beijing 100039 (China) 31nstitute of Plant Nutrition and Resources, Bezjing Academy of Agricultural and Forestry Sciences, Beijing 100089 (China) (Received December 12, 2005; revised February 17, 2006)
ABSTRACT A field experiment was conducted on Chinese cabbage (Brassica campestris L. ssp. pekinensis (Lour.) Olsson) in a Nanjing suburb in 2003. The experiment included 4 treatments in a randomized complete block design with 3 replicates: zero chemical fertilizer N (CK); urea at rates of 300 kg N ha-' (U300) and 600 kg N ha-' (USOO), both as basal and two topdressings; and polymer-coated urea at a rate of 180 kg N hap1 (PCU180) as a basal application. The acetylene inhibition technique was used to measure denitrification (N2 N20) from intact soil cores and N 2 0 emissions in the absence of acetylene. Results showed that compared to CK total denitrification losses were significantly greater ( P 5 0.05) in the PCU180, U300, and U600 treatments, while NzO emissions in the U300 and U600 treatments were significantly higher ( P 5 0.05) than CK. In the U300 and U600 treatments peaks of denitrification and NzO emission were usually observed after N application. In the polymer-coated urea treatment (PCU180) during the period 20 to 40 days after transplanting, higher denitrification rates and N z 0 fluxes occurred. Compared with urea, polymer-coated urea did not show any effect on reducing denitrification losses and NzO emissions in terms of percentage of applied N. As temperature gradually decreased from transplanting to harvest, denitrification rates and N z 0 emissions tended to decrease. A significant ( P 5 0.01) positive correlation occurred between denitrification ( r = 0.872) or NzO emission ( r = 0.781) flux densities and soil temperature in the CK treatment with a stable nitrate content during the whole growing season.
+
Key Words:
denitrification loss, N z 0 emission, polymer-coated urea, urea, vegetable field
Nitrogen fertilization is crucial for achieving high yields in field vegetables (Li et al., 2000; Sun et al., 2003). Unfortunately, because they cause severe environmental problems, such as nitrate leaching, nitrous oxide (N2 0) emissions, and ammonia volatilization, many current intensive systems of vegetable production are not sustainable (Neeteson and Carton, 2001; Li et al., 2003). For example, in an irrigated vegetable field 14%-52% of the N input was found to be lost through denitrification (Ryden and Lund, 1980). Also, Tei et al. (1999) reported that significant quantities of miheral nitrogen were left in the soil after vegetable harvest, leading to potential risk of N leaching. Nevertheless, in order to obtain high yields, growers usually apply large amounts of N fertilizer. A survey in a Beijing suburb showed that farmers' N application rates for vegetables were over twice recommended rate, and the average residual soil mineral nitrogen content within 1 m depth was 412 kg N ha-', which was susceptible to nitrate leaching and denitrification (Li et al., 2000). Another survey in Shandong Province showed that in comparison with normal vegetable fields, N application rates were much higher and nitrogen loss was more serious in protected vegetable fields (Li et al., 2000). In the soil-plant system nitrification and denitrification are two important nitrogen transformation processes, both of which can produce NzO. Nitrous oxide is not .only one of the greenhouse gases contributing to global warming, but it also directly destroys the stratospheric ozone layer. Many factors *'Project supported by the National Natural Science Foundation of China (No. 40171048) and the Science and Technique Key Project of the Tenth Five-Year Plan of China (No. 2002BA516A03). *2Corresponding author. Email: [email protected].
DENITRIFICATION AND N20 EMISSIONS
39 1
affect denitrification loss and N2O emission, such as temperature, soil moisture, available C and N, as well as rate and type of N fertilizer (Eichner, 1990; Granli and Bockman, 1994; Su et al., 2005). About 70% of all anthropogenic N 2 0 emissions are from agriculture activity (Delgado and Mosier, 1996) with chemical nitrogen fertilization being considered the dominant source for N 2 0 emissions from agricultural soils. The intensity of the processes causing N20 emissions from cultivated soils is closely linked to fertilization rates (Mosier and Kroeze, 2000; Kaiser et aZ., 1998). To date, some research in China has been conducted on denitrification and N 2 0 emissions from cereal fields (Ding et al., 2001; Zhang et al., 2001; Zhang et al., 2004; Zou et al., 2002; Xiong et al., 2003), but little has been done with vegetable fields. One possible way to improve nitrogen use efficiency and to reduce environmental hazards is the use of controlled-release fertilizers (Shoji, 1999; Shaviv, 2001). The effectiveness of a fertilizer mainly depends on the extent t o which N supply matches plant demand (Shaviv, 2001). Controlled-release fertilizers have advantages, such as saving labor (only a single basal application within the whole plant growth period is needed), improving N use efficiency thereby allowing for a reduction of fertilizer application rate, decreasing NO, leaching as well as NzO and NO emissions, and maintaining high crop yields with good quality (Shoji and Kanno, 1994; Watanabe et al., 1999; Kosuge et al., 2001; Shoji et al., 2001; Cheng et al., 2002; Zheng et al., 2004). Recently, there has been an increase in studies on the effects of controlled-release fertilizers on crop growth and environmental problems in upland fields (Kosuge et al., 2001). The present study aimed to measure differences in denitrification losses and NzO emissions as well as mineral nitrogen (NHi-N and NOT-N) among a control, urea, and polymer-coated urea applied to a Chinese cabbage (Brassica campestris L. ssp. pekinensis (Lour.) Olsson) field. MATERIALS AND METHODS
Field experiment The experiment was carried out on a vegetable field of the Dongyang Scientific and Technical Station in the eastern suburb of Nanjing, Jiangsu Province, China, in 2003. The soil was an Agric Ferri-udic Argosol (Cooperative Research Group on Chinese Soil Taxonomy, 2001), with (in 0-20 cm) a pH (HZO) of 7.69, organic matter of 25.3 g kg-', total N of 1.52 g kg-', total P of 2.75 g kg-', total K of 22.9 g kg-', available P (Olsen P) of 48.0 mg kg-', and available K of 135 mg kg-'. The soil bulk density was 1.40 g ~ m - ~ . In this experiment, 4 treatments were included: a control (without chemical N fertilizer) (CK), a conventional nitrogen application rate of 600 kg N ha-' as urea (USOO), a reduced N application rate of 300 kg N ha-' as urea (U300), and a polymer-coated urea at a rate of 180 kg N ha-' (PCU180). Treatments were laid out in a randomized complete block design with three blocks, and the area of each plot was 25 m2 (5.0 m x 5.0 m). In addition, before transplanting seedlings 30 t pig manure ha-' with 11 g kg-l nitrogen content, 150 kg P205 ha-' as calcium monophosphate, and 150 kg K2O ha-' as potassium chloride were applied t o each plot. The manure, P, and K fertilizers as well as the urea (except for polymer-coated urea) were broadcasted on the soil surface and then plowed and harrowed. Polymer-coated urea (manufactured by the Institute of Plant Nutrition and Resources, Beijing Academy of Agricultural and Forestry Sciences) was applied as a band below the seedling in a single basal application as suggested by Shoji e t al. (2001) and Cheng et al. (2002). For the U300 and U600 treatments, urea was applied 3 times including one basal application with 25% of the total applied N and two topdressings with 25% on the 26th day and 50% on the 50th day after transplanting. For N topdressing, urea was broadcasted and immediately followed by irrigation of about 150 m3 ha-l with the same amounts of water being applied to the CK and PCU180 treatments. On September 4 following basal dressing, Chinese cabbage seedlings were transplanted with a density of 40 cm x 50 cm. The crop was irrigated daily during the first 4 days after transplanting and harvested on December 6, 2003.
392
B. CAO
et al.
Measurements and data analyses To measure the release of polymer-coated urea under field conditions five grams of polymer-coated urea was enclosed in a total of 18 plastic, about 1 mm mesh, net bags and buried during transplanting at a 10 cm soil depth. Three bags were retrieved on days 3, 7, 19, 30, 41, and 5 2 after transplanting. The remaining urea N in the bag was measured by the colorimetric method (Yamasoe, 1976), and then released urea N was calculated by subtracting the remaining urea N from total N. Denitrification losses were measured using the intact soil core-acetylene (C2H2) inhibition technique (Ryden et al., 1987). In the presence of C2H2, the reduction of N 2 0 to N2 gas was inhibited, so the denitrification loss was calculated from N20-N production. In the absence of C2H2, the N 2 0 production alone was used as an estimate of NzO emission. The soil core sampler (32 mm diameter and 150 mm deep) and the gas-tight PVC incubator (150 mm diameter by 150 mm deep) were the same as described by Cai et al. (2002). Duplicate sets of 8 soil cores were taken from each block and placed into incubators for all the treatments. The 8 soil cores were randomly taken in the CK, U300, and U600 treatments, while in the PCU180 treatment 4 soil cores were sampled close to the fertilizer band and the other 4 soil cores were taken from the middle of two rows. Each incubator lid was fitted with a rubber stopper for C2H2 amendment and gas sampling. After the lid was closed, about 500 mL of air was withdrawn from the incubator followed by addition of 180 mL of purified C2Hz (about 10% (v/v) CzH2 in the headspace). Thereafter, air was added to adjust to normal pressure. To maintain the same temperature and avoid complications due to diurnal temperature fluctuations, the incubators were kept for 24 h in a hole at the same depth adjacent to the experimental plots and covered with a thin layer of soil. After 24 h, a 20-mL gas sample was taken and transferred to an 18-mL gas-tight glass bottle. A subsample was analyzed for N 2 0 using an Agilent 4890D gas chromatograph equipped with a Poropak-Q packed column and an electron capture detector (ECD). The Poropak-Q was connected in series through a computer-controlled 6-valve system to backflush any volatile fluoride and chloride compounds. The flow rate was 30 cm3 min-l. Column and detector temperatures were 55 and 330 "C, respectively. After gas sampling, the soil samples were taken from the incubators without C2H2 for mineral N and soil water content analyses. Field moisture soil samples were extracted by shaking with 2 mol L-' KC1 solution (1:5 soil-solution ratio) for 1 h followed by filtration. The extracts were analyzed for NH,f-N and NO,-N using steam-distillation procedures. Gravimetric soil water content (oven-dried at 105 "C) was measured and water-filled pore space (WFPS) was calculated (Granli and Berckman, 1994). All measurements commenced 1 day after basal dressing and lasted for 93 days, which was just before harvest. Samples were taken around every 2-3 days after each N application and then at longer intervals. There were a total of 13 sampling times with 3 replicates at each sampling time. N2O loss during intervals between 2 sampling times was calculated as the average of the 2 measurements. In addition, the soil temperature at a depth of 7.5 cm was measured. Denitrification losses and N 2 0 emission fluxes for the four treatments measured throughout the Chinese cabbage growing season were compared. Also differences in means of NH,f-N and NO,-N for the four treatments were compared. A correlation analysis for denitrification or N2O emission flux densities and soil temperature was utilized. Statistical significance of total denitrification losses and N 2 0 emissions from the four different treatments was determined with ANOVA and mean separation using least significant difference (LSD) with P 5 0.05. RESULTS AND DISCUSSION
Mineral nitrogen During the Chinese cabbage growing season, application of chemical N fertilizer generally increased mineral N content in the soil (Fig. 1). In the CK treatment (without chemical N fertilizer), soil min-
DENITRIFICATION AND N2O EMISSIONS
393
era1 N, the sum of NH:-N and NOT-N, was low, being less than 8 mg kg-'. For the U300 and U600 treatments, peaks of NHl-N and NO,-N occurred shortly after N application with higher peaks in the U600 treatment, except for the first topdressing on day 26 with delayed sampling due to consecutive days of rainfall after the fertilization. The highest peaks of NHi-N and NO,-N occurred after the second topdressing (50% of the total applied N on day 50). NHl-N in the soil decreased quickly from its maximum value, while NO,-N decreased relatively slowly, especially after the second N topdressing where NOT-N of the U600 treatment remained at high levels (52 mg kg-') until the end of the experiment (Fig. 1). This phenomenon could partly be explained by the weak N uptake of the crop (personal communication). 100
-e C K
h
80
7
m
+ PCU180
Y
-
60
2
40
E
-c U300
-
100 8o
x
60 v
I
z
-
40
z
20
2
t
0
20
0
0 20
100
40 60 80 Days after transplanting
0
20
0
40
60
80
100
Days after transplanting
Fig. 1 Mineral nitrogen contents (means f SD) in 0-15 cm soil during the growing season of a Chinese cabbage field: NHZ-N (a) and NO,-N (b). The arrows at day 26 and day 50 indicate time of topdressing of urea at a conventional nitrogen application rate of 600 kg N hav1 (USOO), urea a t a reduced N application rate of 300 kg N hap1 (U300), and polymer-coated urea at 180 kg N ha-' (PCU180) with a control without chemical N fertilizer (CK).
Additionally, during the first 10 days after transplanting mineral N content of the PCU180 treatment was comparable to that of CK (Fig. 1). By the 20th day after transplanting, however, NH,f-N and NO;N in the PCU180 treatment increased to 10.3 mg kg-' and 30.1 mg kg-', respectively, which was the highest among the four treatments. The high level lasted for around 20 days and then decreased. The mineral N pattern of the PCU180 treatment was in accordance with the pattern of release rate of the polymer-coated urea (Fig. 2). 4 r I
-c'n X
3 -
4C K
3
--c U300
2
-x-
PCU180
27
+-a
g.c
sz zo, ' E Z 1
ill% -
zs
20
a,
n
3-
0
0
I
0
15
30
45
Days after transplanting Fig. 2
U600
60
0 0
20 40 60 80 Days after transplanting
100
Cumulative nitrogen released (means f SD) from polymer-coated urea during the Chinese cabbage growing season.
Fig. 3 Denitrification flux from different treatments during the growing season of a Chinese cabbage field. The arrows at day 26 and day 50 indicate time of topdressing of urea at a conventional nitrogen application rate of 600 kg N ha-' (USOO), urea at a reduced N application rate of 300 kg N ha-' (U300), and polymer-coated urea at 180 kg N hap1 (PCU180) with a control without chemical N fertilizer (CK).
Denitrification loss and
N2 0
emission
Denitrification and NzO fluxes during the Chinese cabbage growing season are shown in Figs. 3 and
B. CAO et at.
394
4, respectively. In general, denitrification and N 2 0 fluxes in the CK treatment (with pig manure, but without chemical N fertilizer) were lower than those of the other three treatments with chemical N fertilizer additions (PCU180, U300 and U600). Except for the PCU180 treatment, maximum denitrification and N2O fluxes were observed on the 3rd day after transplanting (basal dressing).
-t
CK
-m-
U300 PCU180
-A-
n
E 10 0
0
20
40
60
80
Days after transplanting
100
-
80
+Temperature n
'
~
~
~
~
3 6 11 2 2 3 6 4 2 4 9 5 4 5 7 6 3 7 3 8 4 9 3
Days after transplanting
Fig. 4 NzO emission flux from different treatments during the growing season of a Chinese cabbage field. The arrows at day 26 and day 50 indicate time of topdressing of urea at a conventional nitrogen application rate of 600 kg N ha-' (USOO), urea at a reduced N application rate of 300 kg N ha-l (U300), and polymer-coated urea a t 180 kg N hap1 (PCU180) with a control without chemical N fertilizer (CK). Fig. 5 Soil temperature ("C) and water content (% water-filled pore space (WFPS)) during the growing season in a Chinese cabbage field.
The maximum denitrification and N 2 0 emission flux densities in CK were 1.68 and 0.08 kg N ha-' d-' , respectively. However, application of urea greatly promoted both denitrification and NzO production with the maximum denitrification rate and N 2 0 flux of the U300 treatment reaching 3.14 and 0.51 kg N ha-' d-', respectively, and the U600 treatment being 3.63 and 1.05 kg N ha-' d-l, correspondingly. Other researchers have also found that a combination of manure with chemical N fertilizer, in comparison to pig slurry alone, significantly increased denitrification and N 2 0 rates shortly after application (Arcara et al., 1999; Yang et al., 2003). For the U300 and U600 treatments, denitrification and N2O emission peaks were also observed after N fertilization except for N2O emission of the U300 treatment after the first urea topdressing (Figs. 3 and 4). Consecutive days of rainfall instantly after the first topdressing for the U300 and U600 treatments made the field too muddy to take soil core samples; consequently possible peaks of mineral N, denitrification and NzO emissions were missed (Figs. 1, 3 and 4). Denitrification and N 2 0 emission peaks for the three chemical N fertilizer treatments (PCU180, U300, and U600) were in accordance with peaks of NH,f-N and NOT-N (Figs. 1, 3 and 4). Figs. 3 and 4 also showed that during the period of 20 to 40 days after transplanting in the polymer-coated urea treatment (PCU180) denitrification rates were higher than those of the other three treatments and N2O fluxes were higher than the CK and U300 treatments. This was because of the higher soil mineral N during this period as shown by the N H l - N and NO,-N levels after transplanting (Fig. 1). Soil moisture of 0-15 cm ranged from 55.4% to 63.3% WFPS during the Chinese cabbage growing season (Fig. 5), which was favorable for denitrification and N 2 0 production (Klemedtsson et aL, 1988). However, soil temperature decreased greatly from about 32 "C at transplanting to about 5 "C at harvest (Fig. 5), which markedly influenced denitrification and N 2 0 emission. The time course of denitrification (Fig. 3) and N 2 0 emissions (Fig. 4) was similar to that of the temperature (Fig. 5) with the highest rates shortly after transplanting and decreasing to very low levels before harvest. 92%-95% of the denitrification losses and 65%-85% of N 2 0 emissions in the 4 treatments occurred before the second topdressing event (data not shown). A significant ( P 5 0.01) positive correlation was shown between denitrification ( T = 0.872) or N 2 0
~
m
DENITRIFICATION AND N2O EMISSIONS
395
emission ( r = 0.781) flux densities and soil temperature for the CK treatment with a stable NO,-N content during Chinese cabbage growing season (Fig. l b ) . The correlation was not shown for the other N fertilized treatments with variable NO,-N contents, which greatly affect the flux densities. Furthermore, when soil temperature dropped below 10 "C after 70 days (Fig.5), denitrification and NzO fluxes for the 4 treatments were very low despite high NO,-N in the U300 and U600 treatments (Fig. lb). This finding indicated that soil temperature was a primary regulator of nitrification-denitrification processes. Temperature markedly affects microorganism activity including that of nitrifiers and denitrifiers. When soil temperature is below 10 "C, denitrification and N2O emissions are barely detectable even though other conditions are favorable (Cho et al., 1975; Aulakh et al., 2001). Table I shows that chemical N fertilization significantly ( P 5 0.05) enhanced total denitrification losses and, except for the PCU180 treatment, N2O emissions. Total NzO emissions derived from chemical N fertilizer ranged from 1.09%-1.63% of applied N, which was similar to the value of 1.25% i 1% frequently used to estimate N 2 0 emissions from N fertilization (Bouwman, 1994). Total denitrification losses derived from chemical N fertilizer ranged from 4.33% to 8.55% of N applied, which was in the range of other reports of direct denitrification loss obtained from vegetable fields (Ryden and Lund, 1980; Bertelsen and Jensen, 1992), but higher than the results of upland cereal crops in China with similar incubation procedures (Zhang et al., 2001, Zhang et al., 2004; Ding et al., 2001; Zou et al., 2002). TABLE I Total denitrification losses and N20 emissions from different treatments during the growing season in a Chinese cabbage field Treatmenta)
Denitrification loss Amount
CK PCU180 U300 U600
Difference
__ kg N ha-' __ 19.8 ab) 35.2 b 15.4 40.1 b 20.3 45.8 b 26.0
N20 emission Percent of applied N
Amount
%
- k g N ha-'
8.55 6.76 4.33
1.77 a 4.71 ab 5.03 b 11.10 c
Difference
2.94 3.26 9.30
__
Percent of applied N
% 1.63 1.09 1.55
~
a)CK--control (without chemical N fertilizer); U6OO-urea at 600 kg N ha-l, a conventional nitrogen application rate; U300-urea at 300 kg N ha-l, a reduced N application rate; and PCU180-polymer-coated urea at 180 kg N ha-'. b)Values within each column followed by the same letter do not differ significantly ( P 5 0.05) using an LSD test.
Compared with other reports which identified the positive effects of controlled-release fertilizers on reduction of denitrification and NzO emissions (Shoji and Kanno, 1994; Shoji et al., 2001; Cheng et al., 2002; Zheng et al., 2004; Minami, 2005), polymer-coated urea compared to urea did not show any effect on reducing denitrification losses or N20 emissions in terms of percentage of applied N in this experiment (Table I). The possible reason was an oversupply of N from the polymer-coated urea resulting in high soil mineral N in the first half of the growing season (Fig. 1),and consequently high denitrification losses and N20 emissions occurred (Figs. 3 and 4). Generally, if the release dynamics of a controlled-release N fertilizer do not match the pattern of N uptake by the plant, the effectiveness of the fertilizer will be reduced and N loss will be increased due to an over-supply N during the period of plant growth or "tailing" effect after harvest (Shaviv, 2001). This was particularly important for upland crops because extreme water and temperature conditions frequently occurred, which markedly influenced the release rate and release period of these controlled-release fertilizers (Takahashi, 1998). ACKNOWLEDGEMENTS We would like t o express many thanks to Dr. Marco Roeckle, Technical University Carolo-Wilhelmina, Braunschweig, Germany, for his comments.
396
B. CAO et al.
REFERENCES Arcara, P. G., Gamba, C., Bidini, D. and Marchetti, R. 1999. The effect of urea and pig slurry fertilization on denitrification, direct nitrous oxide emission, volatile fatty acids, water-soluble carbon and anthrone-reactive carbon in maize-cropped soil from the Po plain (Modena, Italy). Biol. Fertil. Soils. 2 9 (3): 270-276. Aulakh, M. S., Khera, T . S. and Doran, J. W. 2001. Denitrification, N 2 0 and C02 fluxes in rice-wheat cropping system as affected by crop residues, fertilizer N and legume green manure. Biol. Fertil. Soils. 34: 375-389. Bertelsen, F. and Jensen, E. S. 1992. Gaseous nitrogen losses from field plots grown with pea or spring barley estimated by 15N mass balance and acetylene inhibition techniques. Plant Soil. 142: 287-295. Bouwman, A. F. 1994. Method to Estimated Direct Nitrous Oxide Emissions from Agricultural Soils. Report 773004004. National Institute of Public Health and Environmental Protection, Bilthoven. Cai, G. X., Chen, D. L., White, R. E., Fan, X. H., Pacholski, A., Zhu, Z. L. and Ding, H. 2002. Gaseous nitrogen losses from urea applied to maize on a calcareous fluveaquic soil in the North China Plain. Aust. J . Soil Res. 40: 737-748. Cheng, W., Nakajima, Y . , Sudo, S., Akiyama, H. and Tsuruta, H. 2002. N20 and NO emissions from a field of Chinese cabbage as influenced by band application of urea or controlled-release fertilizers. Nutrient Cycling in Agroecosystems. 63: 231-238. Cho, C. M., Sakdinan, L. and Chang, C. 1975. Denitrification intensity and capacity of three irrigated Alberta soils. Soil Sci. SOC. Am. J . 43: 945-950. Cooperative Research Group on Chinese Soil Taxonomy. 2001. Chinese Soil Taxonomy. Science Press, Beijing. 203pp. Delgado, J . A. and Mosier, A. R. 1996. Mitigation alternatives to decrease nitrous oxides emissions and urea-nitrogen loss and their effect on methane flux. J . Enwiron. Qual. 25: 1105-1 111. Ding, H., Cai, G. X., Wang, Y. S. and Chen, D. L. 2001. Nitrification-denitrification losses of nitrogen fertilizer and N 2 0 emission from maize-chao soil system in North China Plain. Scientia Agricultura Sinica (in Chinese). 34(4): 416-421. Eichner, M. J . 1990. Nitrous oxide emissions from fertilized soils: Summary of available data. J . Enwiron. Qzlal. 19: 2 72-2 80. Granli, T . and B@ckman,0. C. 1994. Nitrous oxide from agriculture. Norwegian Journal of Agricultural Sciences. (Supplementl2): 7-128. Kaiser, E. A., Kohrs, K., Kucke, M., Schnug, E., Munch, J. C. and Heinemeyer, 0. 1998. Nitrous oxide release from cultivated soils: Influence of different N-fertilizer type. Biol. F e d . Soils. 28: 36-43. Klemedtsson, L., Svensson, B. H. and Rosswall, T. 1988. Relationships between soil moisture content and nitrous oxide production during nitrification and denitrification. Biol. Fertil. Soils. 6: 106-111. Kosuge, S., Higashi, T. and Saigusa, M. 2001. Effect of controlled availability fertilizers on tomato cultivation by single basal application. Jpn. J. Soil Sci. Plant Nutr. (in Japanese). 72(5): 621-625. Li, X. L., Zhang, F. S. and Mi, G. H. 2000. Fertilizing for Sustainable Production of High Quality Vegetables (in Chinese). China Agricultural University Press, Beijing. 443pp. Li, J. L., Chen, X. P., Li, X. L. and Zhang, F. S. 2003. Effect of N fertilization on yield, nitrate content and N apparent losses of Chinese Cabbage. Acta Pedologica Sinica (in Chinese). 40(2): 261-266. Minami, K . 2005. N cycle, N flow trends in Japan, and strategies'for reducing NzO emission and NO, pollution. Pedosphere. 15(2): 164-172. Mosier, A. and Kroeze, C. 2000. Potential impact on the global atmospheric NzO budget of the increased nitrogen input required to meet future global food demands. Chemosphere: Global Change Sci. 2: 465-473. Neeteson, J. J. and Carton, 0. T. 2001. The environmental impact of nitrogen in field vegetable production. Acta Hort. 563: 21-28. Ryden, J. C. and Lund, L. J. 1980. Nature and extent of directly measured denitrification loss from some irrigated vegetable crop production units. Soil Sci. SOC.Am. J . 40: 505-511. Ryden, J. C . , Skinner, J. H. and Nixon, D. J. 1987. Soil core incubation system for the field measurement of denitrification using acetylene-inhibition. Soil Biol. Biochem. 19: 753-757 Shaviv, A. 2001. Advances in controlled-release fertilizers. Advances in Agronomy. 71: 1-49. Shoji, S. 1999. Meister Controlled Release Fertilizers-Properties and Utilization. Konno Printing Co., Ltd., Sendai. 160pp. Shoji, S. and Kanno, H. 1994. Use of polyolefin-coated fertilizers for increasing fertilizer efficiency and reducing nitrate leaching and nitrous oxide emissions. Fed. Res. 39: 147-152. Shoji, S., Delgado, J., Mosier, A. and Miura, Y . 2001. Use of controlled release fertilizers and nitrification inhibitors to increase nitrogen use efficiency and to conserve air and water quality. Commun. Soil Sci. Plant Anal. 32(7&8): 1051-1 070. Su, C. G., Yin, B., Zhu, Z. L. and Shen, Q. R. 2005. Gaseous loss of nitrogen from fields and wet deposition of atmospheric nitrogen and their environmental effects. Soils (in Chinese). 37(2): 113-120. Sun, Q., Ding, F. R., Li, P., Lu, H. X., Hu, X. and Liu, Z. J. 2003. Influence of nitrogen on nitrate accumulation in cabbage and N fertilizer application rate. Soils (in Chinese). 35(3): 255-258. Takahashi, M. 1998. Innovation of fertilizer application by using controlled-release fertilizers. 5. Application of fertilizer in vegetable planting (2). J p n . J . Soil Sci. Plant Nutr. (in Japanese). 69(3): 303-309.
DENITRIFICATION AND N 2 0 EMISSIONS
397
Tei, F., Benincasa, P. and Guiduci, M. 1999. Nitrogen fertilization of lettuce, processing tomato and sweet pepper: Yield, nitrogen uptake and the risk of nitrate leaching. Acta Hort. 506: 61-67. Watanabe, T., Ishikawa, T. and Minami, K. 1999. Mitigation of nitrous oxide emission by controlled availability fertilizer and nitrification inhibitor. Jpn. J. .Soil Sci. Plant Nutr. (in Japanese). 70(6): 747-753. Xiong, Z. Q., Xing, G. X., Tsuruta, H., Shi, S. L., Shen, G. Y. and Du, L. J. 2003. Nitrous oxide emissions from paddy soils as affected by incorporation of leguminous green manure and fertilization during double-cropping rice-growing season. Acta Pedologica Sznica (in Chinese). 40(5): 704-710. Yamasoe, B. 1976. Fertilizer Analysis Method (in Japanese). Yokanto Co., Ltd., Tokyo. pp. 60-67. Yang, X. M., Drury, C. F., Reynolds, W. D., Tan, C. S. and Mckenney, D. J. 2003. Interactive effects of composts and liquid pig manure with added nitrate on soil carbon dioxide and nitrous oxide emissions from soil under aerobic and anaerobic conditions. Can. J . Soil Sci. 83(4): 343-352. Zhang, Y. M., Chen, D. L., Zhang, J. B., Edis, R., Hu, C. S. and Zhu, A. N. 2004. Ammonia volatilization and denitrification losses from an irrigated maize-wheat rotation field in the North China Plain. Pedosphere. 14(4): 533-540. Zhang, Y. M., Dong, W. X., Zeng, J. H. and Chen, D. L. 2001. Dynamics of denitrification and N20 flux in maize field. Chinese Journal of Eco-Agriculture (in Chinese). 9(4): 70-72. Zheng, S. X., Liu, D. L., Nie, J., Dai, P. A. and Xiao, J. 2004. Fate and recovery efficiency of controlled release nitrogen fertilizer in flooding paddy soil. Plant Nutrition and Fertilizer Science (in Chinese), lO(2): 137-142. Zou, G. Y., Zhang, F. S. and Li, X. H. 2002. Study on nitrification-denitrificationof soil nitrogen in summer maize season. AgriculturaZ Research in the Arid Areas (in Chinese). 20(1): 30-34.