Article pubs.acs.org/JAFC
Use of Nitrogen Isotope To Determine Fertilizer- and Soil-Derived Ammonia Volatilization in a Rice/Wheat Rotation System Xu Zhao,† Xiaoyuan Yan,† Yingxin Xie,§ Shenqiang Wang,*,† Guangxi Xing,*,† and Zhaoliang Zhu† †
State Key Laboratory of Soil and Sustainable Agriculture, Changshu National Agro-Ecosystem Observation and Research Station, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China § National Engineering Research Center for Wheat, State Key Laboratory of Wheat and Maize Crop Science, Collaborative Innovation Center of Henan Grain Crops, Henan Agricultural University, Zhengzhou 450002, China ABSTRACT: The nitrogen (N) isotope method reveals that application of fertilizer N can increase crop uptake or denitrification and leaching losses of native soil N via the “added N interaction”. However, there is currently little evidence of the impact of added N on soil N losses through NH3 volatilization using 15N methodologies. In the present study, a three-year rice/ wheat rotated experiment with 30% 15N-labeled urea applied in the first rice season and unlabeled urea added in the following five crop seasons was performed to investigate volatilization of NH3 from fertilizer and soil N. We found 9.28% of NH3 loss from 15 N urea and 2.88−7.70% declines in 15N-NH3 abundance occurred during the first rice season, whereas 0.11% of NH3 loss from 15 N urea and 0.02−0.21% enrichments in 15N-NH3 abundance happened in the subsequent seasons. The contributions of fertilizer- and soil-derived N to NH3 volatilization from a rice/wheat rotation were 75.8−88.4 and 11.6−24.2%, respectively. These distinct variations in 15N-NH3 and substantial soil-derived NH3 suggest that added N clearly interacts with the soil source contributing to NH3 volatilization. KEYWORDS: NH3 volatilization, 15N-labeled urea, 15N-NH3 abundance, 15N variation, soil-derived NH3
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atmospheric pollution.13−15 Intensive efforts have been made to understand the mechanisms of NH3 emission and its controlling factors,12,16 assessment of NH3 volatilization and environmental consequence,17,18 and development of strategies for reducing NH3 loss19 at different scales. The conventional difference method (i.e., NH3 emission in N-treated plots minus that in no N controls divided by total added N) is often used to qualify the volatilization of NH3 after fertilizer application.20 However, this method may have an unintended side effect on assessment of fertilizer and soil native N loss via NH3 volatilization, likely due to the added N interaction as discussed above. Because the added N interaction is generally more obvious following addition of NH4+ than other forms of N, the N interaction may affect NH3 volatilization of both fertilizerand soil-derived N.7 Currently, very little field 15N evidence is available to support the implications of occurrence of the added N interaction on the NH3 volatilization process. Moreover, to our knowledge no attempt has been made to use the 15N methodology to directly determine the fertilizer contributions to NH3 volatilization. Although previous field studies21−23 have sometimes included the 15N isotope as part of their assessment of NH3 volatilization loss using the 15N balance (i.e., calculated as a difference between the added amount and the recovered amount of 15N in plants and soils), the direct measurement of 15 N in volatilized NH3 and discrimination of fertilizer- and soilderived NH3 in fields treated with 15N-labeled fertilizer is rare.
INTRODUCTION The 15N isotope can be used to directly investigate the fate of fertilizer nitrogen (N) applied to crops and can distinguish soiland fertilizer-derived N.1 This approach revealed that uptake of soil native N by crops is increased when fertilizer is applied, and less fertilizer N was recovered compared with the conventional difference method (calculated from the difference in N uptake by plants between the plot receiving N and the no N addition control).2−4 This phenomenon is due to the “added N interaction” 5−7 (sometimes also appropriately called a “priming” effect),8,9 and it can increase the mobility of soil N reserves and conserved fertilizer N through pool substitution, displacement reactions, or immobilization, especially when ammonium (NH4+)-based fertilizers are added.7 Besides being absorbed by crop plants, once mobilized by added N interaction, soil N is more likely to be lost from the soil plant system. Indeed, increased soil-derived N loss through denitrification and NO3− leaching after addition of NH4+ has been reported in previous studies using the 15N tracing methods.10,11 Such losses of soil N due to the added N interaction cannot be simply accounted for by the conventional difference method (i.e., the difference in N loss between plots receiving N and controls not receiving N), which may inappropriately ascribe this native soil N loss to fertilizer N loss, despite the fact that this increased soil-derived N loss is still fertilizer-induced and the net effect of added N interaction on measured cumulative N loss may be very small due to the common occurrence of pool substitution.7 Volatilization of ammonia (NH3) is one of the main ways in which N is lost following application of NH4+-based fertilizers to agricultural fields,12 which not only results in low fertilizer efficiency but also causes soil acidification, eutrophication, and © 2016 American Chemical Society
Received: Revised: Accepted: Published: 3017
December March 19, March 29, March 29,
15, 2015 2016 2016 2016 DOI: 10.1021/acs.jafc.5b05898 J. Agric. Food Chem. 2016, 64, 3017−3024
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Journal of Agricultural and Food Chemistry
Figure 1. Schematic view of a continuous air flow enclosure system for measuring NH3 volatilization.
In this study, therefore, we investigated the abundance of 15N in NH3 and determined the relative contributions of soil and fertilizer N in NH3 volatilization in a paddy soil under conventional N fertilization for three consecutive rice/wheat rotation years. In particular, the duration of residual effects of 15 N applied in the first crop season on NH3 volatilization was also examined over five subsequent crop seasons to address the long-term contributions of the fertilizer N.
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For urea application, 40% was basally applied, 30% was top-dressed at the tillering stage, and another 30% was top-dressed at the ear differentiation stage during each crop season. Super phosphate (60 kg P2O5 ha−1) and potassium chloride (120 kg K2O ha−1) were applied basally in rice and wheat seasons. Only basal fertilizers were incorporated into the plowed layer, and all other fertilizers were applied to the surface. Both rice and wheat were transplanted at a density of 100 plants m−2. Midseason aeration was performed for ∼1 week to improve rice root growth, and a final drainage step was included for maturing and harvesting of rice. Drainage was achieved by allowing flooded water to naturally percolate downward through the soil, and surface drainage was not performed. Flooded water was maintained at a depth of 5 cm in all plots during the rice season except during the midseason aeration and final drainage. There was no irrigation performed during wheat growth, and rainwater was the only source of soil moisture. Measurements of Volatilized NH3 and 15N abundance. NH3 was measured using a modified continuous air flow enclosure method (Figure 1)26 and twice each day (at 8:00−10:00 a.m.and at 2:00−4:00 p.m.) after each urea application for at least a week, until NH3 was no longer detected.27 The diameter of the volatilization chamber was 200 mm; its volume could be adjusted by changing the depth to which it was inserted into the soil or water of each plot. The rate of air flow was set at 15−20 times that of the chamber volume per minute using a pump. For each measurement, the NH3 captured from the air was continuously pumped through an adsorbent solution containing 2% H3BO3 mixed with an indicator composed of methyl red, bromocresol green, and ethanol for 2 h. This adsorbent solution was titrated with a predetermined acid solution to determine the amount of trapped NH3. The total NH3 volatilization flux was calculated as the sum of the daily volatilization rates over the period. After titration, the solutions were mixed to form a composite sample for the analysis of the 15N abundance in NH3 volatized after each urea application. Briefly, the solution was redistilled in steam using 10 mol L−1 NaOH, and the NH3 was recollected into 0.1 mol L−1 of H2SO4 solution.28 The solution was concentrated to a volume of 10 mL in an 80 °C water bath, transferred to a pyriform bottle, and then dried at 80 °C in an oven.29 15N abundance values were determined by an isotope ratio mass spectrometer (MAT-251, USA), with an analytic error of ±0.02%. After harvesting, three soil cores (1 cm diameter, 15 cm depth) were removed from each microplot and mixed to obtain a homogeneous composite sample for the analysis of N content and 15 N abundance, which were determined using the Kjeldahl method and MAT-251.25
MATERIALS AND METHODS
Site Description. The experiment was carried out for six consecutive rice/wheat crop rotation seasons between 2004 and 2006 on three replicate field microplots (1.14 m in diameter) at the Changshu National Agro-Ecosystem Observation and Research Station, Chinese Academy of Sciences (31°32′45″ N, 120°41′57″ E). The site is in the Taihu Lake region of China and has a typical humid subtropical monsoon climate with an average annual temperature of 15.5 °C and an average annual precipitation of 1038 mm. The paddy soil used was classified as Hydragric Anthrosols.24 The pH (water) of the top 15 cm of soil was 6.05, and the soil contained 16.1 g kg−1 organic carbon and 1.31 g kg−1 total N, and showed a 15.0 cmol kg−1 cation exchange capacity (CEC). The top 15 cm soil layer in the field consists of 20.9% sand, 53.5% silt, and 25.6% clay by volume. The natural 15N abundance of the soil N was 0.364%. Soil pH was measured in a 1:2.5 (v/v) soil-to-water ratio using a pH meter. Soil organic carbon was determined by the wet digestion method, soil N content was measured using the Kjeldahl method, and soil CEC was measured using the ammonium acetate method, following soil agrochemical analytical procedures.25 Experimental Design. The microplots were cultivated under a conventional summer flooded rice/winter upland wheat yearly rotation and were surrounded by paddy fields subjected to normal water and fertilization management practices. Observation was formally started at the beginning of the rice-growing season in 2004 (the first rice season). Briefly, 30.0% 15N-labeled urea was applied at a rate of 300 kg N ha−1 to each plot, and unlabeled urea (with a natural 15N abundance of 0.366%) was applied in the subsequent five growing seasons at rates of 250 (the second, fourth, and sixth wheat seasons) and 300 kg N ha−1 (the third and fifth rice seasons), respectively. This allowed us to determine the contribution made to NH3 volatilization from fertilizer N and soil N in each crop season and to investigate the residual effects of 15N applied during the first season on NH3 volatilization in the subsequent five seasons. 3018
DOI: 10.1021/acs.jafc.5b05898 J. Agric. Food Chem. 2016, 64, 3017−3024
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Journal of Agricultural and Food Chemistry
Figure 2. 15N abundances in volatilized NH3 following each N application into a rice/winter rotated paddy field treated with 30% 15N-labeled urea in the first rice season and with unlabeled urea during the following five seasons. For urea application, 30% was basally applied (BA), 40% was topdressed at the tillering stage (TD1), and another 30% was top-dressed at the panicle initiation stage of each crop (TD2). Data are means of triplicate experiments ± standard deviation.
Figure 3. Examination of natural 15N abundance in volatilized NH3 from a summer rice/winter wheat rotation system in paddy soil treated with unlabeled urea over three rotation years. Measurements were made in two Hydragric Anthrosols13 paddy soils following three conventional urea applications. Volatilized NH3 was collected using a continuous air flow enclosure following each N application and subjected to 15N analysis. The line and square within the box represent the median and mean values of all data (n = 33); the bottom and top edges represent the 10th and 90th percentiles, respectively; and the bottom and top bars represent minimum and maximum values, respectively. All figures were drawn with OriginPro 8.5 software (OriginLab, USA), and statistical analysis was conducted with SAS (SAS Institute Inc., USA). Data are presented as means of triplicate experiments or three yearly replicates. Lower case letters indicate statistical significance at p < 0.05.
rice season, despite the addition of 30.0% 15N-labeled urea (Figure 2). Because background air NH3 was removed before atmospheric air was pulled into the chamber in the current continuous air flow enclosure (Figure 1), this indicates that the signal from 15NH3 derived from added labeled N might be diluted significantly by NH3 derived from native soil N. By comparison, volatilized NH3 consistently contained a relatively higher proportion of 15N ranging from 0.382 to 0.578% during the following five crop seasons, despite the application of unlabeled urea containing only 0.366% 15N. Moreover, these
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RESULTS AND DISCUSSION Variations in 15N Abundance of Volatilized NH3. Volatilized NH3 after each urea application exhibited a consistently lower 15N abundance of 22.3−27.1% in the first 3019
DOI: 10.1021/acs.jafc.5b05898 J. Agric. Food Chem. 2016, 64, 3017−3024
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Journal of Agricultural and Food Chemistry values were always greater than the normal 15N abundances of NH3 emitted from untreated control paddy soils (from 0.357 to 0.371% with an average of 0.364%; n = 33; Figure 3). Clearly, these results suggest that NH3 derived from added unlabeled urea in the subsequent five seasons is enriched with 15NH3 derived from the residual 15N applied during the first season. The greater 15N abundance of soil N following each crop harvest in the study plots (0.702−0.833%; Table 1) than the
application of NH4+-based fertilizer is generally thought to be predominantly derived from fertilizer source, because the increased NH4+ concentration can enhance the equilibrium vapor pressure of NH3 in the solution, promote reactions toward the right, and thus increase NH3 volatilization of fertilizer N.12 However, the interaction between fertilizer N and soil N is excluded from these equilibria. The distinct 15N dilution or enrichment phenomena in volatilized NH3 from rice−wheat rotated paddy soil provide strong evidence of the participation of soil N in the NH3 volatilization process (Figure 2). It may therefore be necessary to modify these to include the added N interaction driven by pool substitution through immobilization and displacement reactions (see Figure 4, eq 2). These modified equilibria could better highlight both the fertilizer- and soil-source contributions to NH3 volatilization in cropland soils and better illustrate the complex biological, chemical, and physical factors underpinning NH3 volatilization.31 Contributions of Fertilizer- and Soil-Derived N to NH3 Volatilization. Accumulated NH3 volatilization was 19.5−35.2 kg N ha−1 for the three rice seasons and 2.02−6.61 kg N ha−1 for the three wheat seasons (Figure 5A). This annual and seasonal variation was likely due to varying climatic conditions and/or paddy field rotations.12 NH3 volatilization across the three rice/wheat rotations averaged 34.1 and 3.63 kg N ha−1 for the rice and wheat season, respectively (Figure 5B). This is comparable to field measurements made previously in this region.4,20,27,32−35 The greater NH3 volatilization in the rice seasons than in the wheat seasons is consistent with previous studies,4,27,35 due to the fact that flooded conditions, strong sunlight, and high temperatures in the summer rice seasons generally facilitate NH3 emission.12 On the basis of mass balance using the calculated NH3 volatilization, 15N abundance of volatilized NH3, fertilizer N, and soil N in each crop season, we could distinguish soilderived and fertilizer-derived NH3 and assess their relative contributions to accumulated NH3 volatilization during each crop season (Table 2). Of the 1.76−23.9 and 0.19−3.53 kg N ha−1 of NH3 volatilization following each N application during the three rice and wheat seasons, fertilizer-derived NH3 accounted for 50.0−93.4 and 78.1−94.9%, whereas the remaining 6.57−50.0 and 5.10−21.9% were derived from soil N, respectively (Figure 5A). The average proportion of fertilizer-derived NH3 of the cumulative NH3 volatilization occurring over the three replicate years was calculated to be only 75.8% for rice seasons and 88.4% for wheat seasons, whereas the remaining 24.2 and 11.6% of NH3 was derived from soil N, respectively (Figure 5B). By comparison, we also calculated these proportions of fertilizer-derived and soil-
Table 1. Changes in 15N Abundance of Soil Total N Following Each Crop Harvest in a Rice/Wheat Rotated Paddy Field Treated with 30% 15N-Labeled Urea in the First Rice Season and with Unlabeled Urea during the Following Five Seasonsa 15
crop season first rice second wheat third rice fourth wheat fifth rice sixth wheat a
N application 30% 15N-labeled urea application at 300 kg N ha−1 unlabeled urea applications at 300 and 250 kg N ha−1 for rice and wheat, respectively; 15N natural abundance of 0.366%
N abundance of soil total N (%)
0.833 ± 0.093 0.792 0.787 0.788 0.715 0.702
± ± ± ± ±
0.039 0.115 0.016 0.078 0.011
Data are means of triplicate experiments ± standard deviation.
natural 15N abundance of the original soil N (0.364%) also supports this notion. Such distinct variations in 15N-NH3 during the six crop seasons in fact indicate that soil N participates in the NH3 volatilization process as well as fertilizer N. These 15N dilution or enrichment effects on volatilized NH3 during the study period may be explained by interchange of fertilizer N with soil N, whereby NH4+-N generated from the hydrolysis of added urea may partially exchange with native soil ammonium derived from microbial metabolism or recalcitrant or bound NH4+-N,5−7,30 which thereafter participates in NH3 volatilization. This phenomenon was similar to that observed in most experiments with 15N-labeled fertilizers, where the interaction between fertilizer N and soil N was commonly detected, and was responsible for the discrepancy in estimation of fertilizer N use efficiency between the isotope recovery and the conventional difference methods.2−4 It is commonly accepted that NH3 volatilization from cropland is mainly composed of a series of physical and chemical reactions mainly governed by NH4+/NH3 equilibria between solid, liquid, and gaseous phases at the soil/water/ atmosphere interface (see Figure 4, eq 1).12 On the basis of this equation, volatilized NH3 from cropland following the
Figure 4. Influence of the added N interaction on NH3 volatilization following application of NH4+-based fertilizer. 3020
DOI: 10.1021/acs.jafc.5b05898 J. Agric. Food Chem. 2016, 64, 3017−3024
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Figure 5. (A) Cumulative NH3 volatilization from paddy soils and the proportion of fertilizer- and soil-derived NH3 during six consecutive rice/ wheat seasons determined by 15N method. Data are means of triplicate experiments + standard deviation. BA, TD1, and TD2 represent basal application and first and second top-dressings of urea at a ratio of 3:4:3 during each crop season. (B) Annually averaged NH3 volatilization and contribution of fertilizer and soil N to volatilized NH3 determined by 15N method. Data are means + standard deviation of three annual replicates. Lower case letters indicate significant differences between rice and wheat seasons (p < 0.05).
Table 2. Details of the 15N Isotope Method for Distinguishing between Soil- and Fertilizer-Derived NH3 Volatilized from Paddy Soil over Six Consecutive Rice/Wheat Seasons proportion of fertilizer- and soil-derived NH3 first rice season (15N-labeled urea)
measurements/definitions cumulative volatilized NH3 amount of fertilizer-derived NH3 (kg N ha−1), Y1 (kg N ha−1), Y 15 N abundance in volatilized NH3 (%), A contribution of fertilizer N to volatilized NH3 (%), C1 15 N abundance in fertilizer N (%),a A1 amount of soil-derived NH3 (kg N ha−1), Y2 15 N abundance in soil N (%),b A2 contribution of soil N to volatilized NH3 (%), C2
subsequent seasons (nonlabeled urea)
Y1 = Y(A − A2)/(A1 − A2)c
Y1 = Y − Y2
C1 = Y1/Y × 100
C1 = 100 − C2
Y2 = Y − Y1 C2 = 100 − C1
Y2 = Y(A − A1)/(A2 − A1)c C2 = Y2/Y × 100
30% 15N-labeled urea was applied during the first rice season. Subsequent crop seasons were treated with nonlabeled urea containing 15N at the naturally occurring abundance of 0.366%. b0.364% for the first rice season. The percentage of 15N in soil N was measured before each subsequent crop planting. cDeduced according to the follow two equations: (1) Y = Y1 + Y2; (2) Y × A = Y1 × A1 + Y2 × A2. a
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DOI: 10.1021/acs.jafc.5b05898 J. Agric. Food Chem. 2016, 64, 3017−3024
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Journal of Agricultural and Food Chemistry derived NH3 using the difference method and the reported average background emission levels of NH3 in this paddy soil from the same region as in this study (Table 3). There was little
and with two previous analyses on increased soil-derived N loss through denitrification and NO3− leaching after addition of NH4+ using the 15N tracing methods.10,11 Such a phenomenon is impossible to be accounted for by the conventional difference method, whereby a fixed value of soil background NH3 volatilization (i.e., the control with no chemical N application) was generally used for calculation,20 and may conceal the actual contributions of fertilizer- and soil-derived N to NH3 volatilization. For example, in a rice paddy of southwestern China with 4.83 kg N ha −1 of soil background NH 3 volatilization, Chen et al.37 reported 22.4−66.4 kg N ha−1 of NH3 volatilized following the application of urea-N at rates of 135−260 kg N ha−1. Using these data in the previous study, the proportion of soil-derived NH3 estimated by the conventional difference method shows a declining trend from 21.6 to 7.28% with increased N rate from 135 to 260 kg N ha−1. These estimated proportions are highly unreliable because all of the calculations are based on the assumption that the amount of soil-derived NH3 remains unchanged regardless of the rate of fertilizer N applied to the soil and the added N interaction.7,9 To distinguish contributions of fertilizer- and soil-derived N to NH3 volatilization, our results suggest that the conventional difference method is an inadequate approach, likely due to the fact that it inappropriately ascribes the increased soil-derived NH3 to fertilizer-derived NH3 and may result in underestimations of soil contributions to NH3 volatilization.7 Estimation of NH 3 emission from agricultural soils commonly utilized emission factors expressed as the percentage of volatilized NH3-N from applied fertilizer N.16,17,38−41 Most of these emission factors are often measured by the traditional nonisotopic methods that do not consider the interaction of fertilizer N and soil N and are therefore, strictly defined, fertilizer-induced rather than fertilizer-derived. In the present study, it should be admitted that certain errors in estimation of proportions of fertilizer- and soil-derived NH3 in rice/wheat rotation system may remain, probably due to the lack of measurements for soil 15N after each N application (Table 1)
Table 3. Relative Contributions of Fertilizer- and SoilDerived NH3 to NH3 Volatilization Estimated Using the Conventional Difference Method crop season rice season wheat season
total NH3 volatilizationa (kg N ha−1)
background NH3 volatilizationb (kg N ha−1)
fertilizerderived (%)
soil-derived (%)
34.1 ± 14.0
0.50
98.3 ± 0.79
1.68 ± 0.79
3.63 ± 2.58
0.39
85.8 ± 7.23
14.2 ± 7.23
a
Average values across three rice/wheat rotations in the current study. According to the average background emission levels of NH3 reported by Zhao et al.4 in the same rice/wheat paddy soil from the same region as in this study. b
difference in proportions of fertilizer- and soil-derived NH3 in the wheat season from the two calculation methods. This is likely due to the very low NH3 emissions following fertilizer application impeded by the relatively lower temperatures in the winter wheat season and the high clay content of the study soil.36 However, we found fertilizer-derived NH3 calculated by the 15N method was far lower in the rice season than that estimated by the difference method, whereas soil-derived NH3 was correspondingly higher when using the 15N method (Table 3). This in fact emphasizes the substantial contribution that soil N makes to volatilization of NH3 in addition to that made by fertilizer N, in particular in the flooded rice season. Clearly, this high proportion (11.6−24.2%) of soil-derived NH3 identified by the 15N isotope method is ascribed to the added N interaction occurring in the current rice−wheat rotated paddy soil. This phenomenon is in agreement with well-document experiments with 15N-labeled fertilizers where increased uptake of soil unlabeled native N by crops was frequently reported2−4
Figure 6. Percentage of volatilized 15N-NH3 following application of 15N-urea over six consecutive rice/wheat seasons. Data are means of triplicate experiments ± standard deviation. 3022
DOI: 10.1021/acs.jafc.5b05898 J. Agric. Food Chem. 2016, 64, 3017−3024
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Journal of Agricultural and Food Chemistry
Promotion Association, Chinese Academy of Sciences (Member 2015249).
and great variations in NH3 volatilization over the three rice and wheat rotations (Figure 5A). Nevertheless, the reliability of distinct variations in 15N-NH3 abundance could be warranted (Figure 2), indicating the impact of the occurrence of added N interaction on fertilizer and soil contributions to NH3 volatilization. Despite having little effect on measured cumulative NH3 volatilization induced by N application, separation of the relative contributions of soil-derived and fertilizer-derived N to NH3 volatilization by 15N isotope analysis on volatilized NH3 may facilitate a more accurate expression and scientific understanding of the environmental consequences of fertilizer N application in different soil types under various crop rotations and climates. The rice seasons produced a lower percentage of fertilizerderived NH3 from cumulative NH3 volatilization than the wheat seasons, but generated more soil-derived NH3 (Figure 5). The added N interaction therefore appeared to be more significant in the rice season, which may be due to increased NH4+ that persists longer in the flooded anaerobic conditions associated with the rice season. Added NH4+-N may be more likely to combine with or substitute for soil native NH4+-N in these conditions,42 whereas added NH4+ is rapidly oxidized to NO3− under the aerobic conditions of the upland wheat season. Azam also reported the added N interaction was generally lower with NO3−-N than with NH4+-N.7 This result suggests that the magnitude of effects from the added N interaction on fertilizer and soil contributions to NH3 volatilization may also vary among different soil environments. Long-Term Residual Effect of Fertilizer 15N to NH3 Volatilization. Although the residual labeled N from the first rice season interchanged with unlabeled N application and could be lost via NH3 volatilization in the subsequent crop seasons (Figure 2), the calculated volatilized NH3 from added 15 N was only 0.11% in total from the following five seasons, which was far lower than the 9.28% 15N-NH3 loss for the first rice season (Figure 6). This is similar to the results from the crop 15N analysis, which showed that almost 30% of the added 15 N was taken up by the first rice, whereas only 6% of the added 15 N was available for crop uptake over the subsequent five seasons (unpublished data). The high proportion of 15N-NH3 loss in the first rice season is mainly due to the distinct flooding practice and climate conditions as mentioned above. The less 15 N-NH3 loss in the subsequent five seasons is likely due to conversion of most residual 15N to more stable organic N compounds or fixed as clay minerals that are not easily lost from the soil,1,2 despite the high residual fertilizer 15N in the soil (Table 1). Our results demonstrate that N fertilizer applied to a flooded paddy is predominantly lost in the first rice season with negligible contribution to NH3 volatilization in subsequent crop seasons.
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Notes
The authors declare no competing financial interest.
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REFERENCES
(1) Stevenson, F. J.; Cole, M. A. Cycles of Soil Carbon, Nitrogen, Phosphorus, Sulfur, Micronutrients, 2nd ed.; Wiley: New York, 1999. (2) Harmsen, K.; Moraghan, J. T. A comparison of the isotope recovery and difference methods for determining nitrogen fertilizer efficiency. Plant Soil 1988, 105, 55−67. (3) Hamid, A.; Ahmad, M. Priming effects of 15N-labelled ammonium nitrate on uptake of soil N by wheat (Triticum aestivum L.) under field conditions. Biol. Fertil. Soils 1993, 15, 279−300. (4) Zhao, X.; Xie, Y. X.; Xiong, Z. Q.; Yan, X. Y.; Xing, G. X.; Zhu, Z. L. Nitrogen fate and environmental consequence in paddy soil under rice-wheat rotation in the Taihu Lake region, China. Plant Soil 2009, 319, 225−234. (5) Jenkinson, D. S.; Fox, R. H.; Rayner, J. H. Interactions between fertilizer nitrogen and soil nitrogen-the so-called ‘priming’ effect. J. Soil Sci. 1985, 36, 425−444. (6) Hart, P. B. S.; Rayner, J. H.; Jenkinson, D. S. Influence of pool substitution on the interpretation of fertilizer experiments with 15N. J. Soil Sci. 1986, 37, 389−403. (7) Azam, F. Added nitrogen interaction in the soil-plant system − a review. J. Agron. 2002, 1, 54−59. (8) Jansson, S. L. Tracer studies on nitrogen transformations in soil with special attention to mineralisation-immoilisation relationships. Ann. R. Agric. Coll. Swed. 1958, 24, 101−361. (9) Kuzyakov, Y.; Friedel, J. L.; Stahr, K. Review of mechanisms and quantification of priming effects. Soil Biol. Biochem. 2000, 32, 1485− 1498. (10) Baraclough, D.; Geens, E. L.; Maggs, J. M. Fate of fertilizer nitrogen applied to grassland. II. Nitrogen-15 leaching results. J. Soil Sci. 1984, 35, 191−199. (11) Azam, F.; Muller, C.; Weiske, A.; Benckiser, G.; Otto, J. C. G. Nitrification and denitrification as sources of atmospheric N2O-role of oxidizable C and applied N. Biol. Fertil. Soils 2002, 35, 54−61. (12) Cai, G. X. In Nitrogen in Soils of China, 1st ed.; Zhu, Z. L., Wen, Q. X., Freney, J. R., Eds.; Kluwer Academic Publishers: Dordrecht, The Netherlands, 1997; pp 193−213. (13) Goulding, K. W. T.; Bailey, N. J.; Bradbury, N. J.; Hargreaves, P.; Howe, M.; Murphy, D. V.; Poulton, P. R.; Willison, T. W. Nitrogen deposition and its contribution to nitrogen cycling and associated soil processes. New Phytol. 1998, 139, 49−58. (14) Bouwman, A. F.; VanVuuren, D. P.; Derwent, R. G.; Posch, M. A global analysis of acidification and eutrophication of terrestrial ecosystems. Water, Air, Soil Pollut. 2002, 141, 349−382. (15) Ye, X. N.; Ma, Z.; Zhang, J. C.; Du, H. H.; Chen, J. M.; Chen, H. Important role of ammonia on haze formation in Shanghai. Environ. Res. Lett. 2011, 6, 024019. (16) Bouwmeester, R. J. B.; Vlek, P. L. G.; Stumpe, J. M. Effect of environmental factors on ammonia volatilization from a urea-fertilized soil. Soil Sci. Soc. Am. J. 1985, 49, 376−381. (17) Bouwman, A. F.; Boumans, L. J. M.; Batjes, N. H. Estimation of global NH3 volatilization loss from synthetic fertilizers and animal manure applied to arable lands and grasslands. Global Biogeochem. Cycles 2002, 16, 1024. (18) Fangmeier, A.; Hadwiger-Fangmeier, A.; Van der Eerden, L.; Jäger, H. J. Effects of atmospheric ammonia on vegetation − a review. Environ. Pollut. 1994, 86, 43−82. (19) Sommer, S. G.; Hutchings, N. Techniques and strategies for the reduction of ammonia emission from agriculture. Water, Air, Soil Pollut. 1995, 85, 237−248. (20) Cao, Y.; Tian, Y.; Yin, B.; Zhu, Z. Assessment of ammonia volatilization from paddy fields under crop management practices aimed to increase grain yield and N efficiency. Field Crops Res. 2013, 147, 23−31.
AUTHOR INFORMATION
Corresponding Authors
*(S.W.) Phone: 86-25-86881012. Fax: 86-25-86881028. E-mail:
[email protected]. *(G.X.) Phone: 86-25-86881019. Fax: 86-25-86881028. E-mail:
[email protected]. Funding
This study was financially supported by the National Natural Science Foundation of China (Grant 30390080), the Special Fund for Environmental Protection in the Public Interest (201309035), and the Foundation of Youth Innovation 3023
DOI: 10.1021/acs.jafc.5b05898 J. Agric. Food Chem. 2016, 64, 3017−3024
Article
Journal of Agricultural and Food Chemistry
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DOI: 10.1021/acs.jafc.5b05898 J. Agric. Food Chem. 2016, 64, 3017−3024
