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. 2017 Jul 21;7(17):6702-6715.
doi: 10.1002/ece3.3211. eCollection 2017 Sep.

Impacts of natural factors and farming practices on greenhouse gas emissions in the North China Plain: A meta-analysis

Cong Xu  1 , Xiao Han  1 , Roland Bol  2 , Pete Smith  3 , Wenliang Wu  1 , Fanqiao Meng  1
Affiliations

Impacts of natural factors and farming practices on greenhouse gas emissions in the North China Plain: A meta-analysis

Cong Xu et al. Ecol Evol. .

Abstract

Requirements for mitigation of the continued increase in greenhouse gas (GHG) emissions are much needed for the North China Plain (NCP). We conducted a meta-analysis of 76 published studies of 24 sites in the NCP to examine the effects of natural conditions and farming practices on GHG emissions in that region. We found that N2O was the main component of the area-scaled total GHG balance, and the CH 4 contribution was <5%. Precipitation, temperature, soil pH, and texture had no significant impacts on annual GHG emissions, because of limited variation of these factors in the NCP. The N2O emissions increased exponentially with mineral fertilizer N application rate, with y = 0.2389e0.0058x for wheat season and y = 0.365e0.0071x for maize season. Emission factors were estimated at 0.37% for wheat and 0.90% for maize at conventional fertilizer N application rates. The agronomic optimal N rates (241 and 185 kg N ha-1 for wheat and maize, respectively) exhibited great potential for reducing N2O emissions, by 0.39 (29%) and 1.71 (56%) kg N2O-N ha-1 season-1 for the wheat and maize seasons, respectively. Mixed application of organic manure with reduced mineral fertilizer N could reduce annual N2O emissions by 16% relative to mineral N application alone while maintaining a high crop yield. Compared with conventional tillage, no-tillage significantly reduced N2O emissions by ~30% in the wheat season, whereas it increased those emissions by ~10% in the maize season. This may have resulted from the lower soil temperature in winter and increased soil moisture in summer under no-tillage practice. Straw incorporation significantly increased annual N2O emissions, by 26% relative to straw removal. Our analysis indicates that these farming practices could be further tested to mitigate GHG emission and maintain high crop yields in the NCP.

Keywords: farming practice; fertilizer; meta‐analysis; methane; natural factor; nitrous oxide.

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Figures

Figure 1
Figure 1
Area‐scaled GHG balance of N2O, CH 4, and N2O+CH 4 under conventional fertilization for (a) wheat season, (b) maize season, and (c) annual period, which are categorized into different levels/types of soil pH, soil texture, and all factors. Figures in parentheses indicate number of observations. All error bars represent 95% confidence intervals
Figure 2
Figure 2
N2O emissions versus cumulative precipitation for (a) wheat season, (b) maize season, and (c) annual period, and N2O emissions versus mean temperature for (d) wheat season, (e) maize season, and (f) annual period. ** represents .01 significance level
Figure 3
Figure 3
Effect of mineral N application rate on N2O emission, CH 4 uptake, and yield relative to no N fertilizer application for (a–c) wheat season, (d–f) maize season, and (g–i) annual period. Horizontal error bars represent standard errors which reflect distribution of N application rate for each N level. Error bars in vertical directions represent 95% confidence intervals of the percentage changes. Figures in parentheses indicate the number of observations
Figure 4
Figure 4
N2O emission and emission factor (EF) versus N application rate for (a) wheat season, (b) maize season, and (c) annual period, and yield versus N application rate for (d) wheat season, (e) maize season, and (f) annual period. EF curves were generated from regression models of N2O emission with N application rate. ** represents .01 significance level.
Figure 5
Figure 5
Effect of no‐tillage on N2O emission, CH 4 uptake, yield, and total GHG balance (area‐scaled and yield‐scaled) for (a) wheat season, (b) maize season, and (c) annual period relative to conventional tillage. Data are expressed as mean percentage changes with 95% confidence intervals (represented by error bars). Figures in parentheses indicate number of observations
Figure 6
Figure 6
Effect of straw incorporation on N2O emission, CH 4 uptake, yield, and total GHG balance (area‐scaled and yield‐scaled) for (a) wheat season, (b) maize season, and (c) annual period relative to straw removal. Effect sizes for N2O emission were separated into no N fertilization and N fertilization. Data are expressed as mean percentage changes with 95% confidence intervals (represented by error bars). Figures in parentheses indicate number of observations
Figure 7
Figure 7
Effect of organic manure and slow‐release fertilizer (SRF) on (a) annual N2O emission, (b) yield, and (c) yield‐scaled N2O emission relative to mineral fertilizer application alone. M + O and RM + O represent full‐dose and reduced mineral N application rates combined with organic manure, respectively; O represents only organic manure applied. Data are expressed as mean percentage changes with 95% confidence intervals (represented by error bars). Yield‐scaled N2O emission represents N2O emission per unit crop yield (Mg). Figures in parentheses indicate number of observations
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