Elsevier

Agriculture, Ecosystems & Environment

Volume 231, 1 September 2016, Pages 218-228
Agriculture, Ecosystems & Environment

Integrated assessment of the impact of enhanced-efficiency nitrogen fertilizer on N2O emission and crop yield

https://doi.org/10.1016/j.agee.2016.06.038Get rights and content

Highlights

  • We assessed the efficacy of EENF on N2O and yield and the key influencing factors.

  • The effectiveness of EENF were similar among crops but varied among products.

  • The efficacy of EENF highly depended on climate, soil and agronomic factors.

  • Surface broadcast and medium N rate were unfavorable for EENF to mitigate N2O.

  • Climate, soil pH and tillage showed less impacts on the efficacy of NI than S/CRF.

Abstract

Enhanced-efficiency nitrogen fertilizer (EENF) has gained considerable attention for improving nitrogen use efficiency and mitigating N2O emission in many agro-ecosystems. However, the effectiveness of EENF is highly variable under field condition. The factors influencing the efficacy of EENF are not well understood. Here, a meta-analysis was conducted to investigate the key factors affecting the efficacy of EENF in upland cropping systems. The effects of EENF were found to be similar among maize, wheat, and barley, while they varied among different EENF products. Inhibitors (IS), including nitrification inhibitors (NI), urease inhibitors (UI), and the combination of UI and NI, significantly mitigated N2O emission and increased crop yield, resulting in a greater reduction in yield-scaled N2O emission compared with slow- or control-releasing fertilizer (S/CRF). Reductions in yield-scaled N2O emission response to IS and S/CRF were both greater in arid regions than in humid regions. Soil pH and texture had less impact on the effect of IS than S/CRF. The efficacy of IS and S/CRF were not significant when N use rates were between 120 and 180 kg N ha−1. Surface broadcasting were unfavorable for mitigating N2O emissions with both IS and S/CRF. The impact of tillage on the efficacy of IS and S/CRF was affected by climate. The effectiveness of S/CRF depended more on these factors than did IS. This meta-analysis highlighted the necessity to connect EENF products with specific climatic, soil, and agronomic attributes for predicting their effectiveness.

Introduction

Synthetic nitrogen (N) fertilizer has played a key role in enhancing crop production to feed 40% of the world’s population since the Haber-Bosch process was invented in the 20th century (Crews and Peoples, 2004). Over the next 40 years, global N fertilizer for crop production is estimated to increase 1.4 fold to meet the projected food demand for 9 billion populations in 2050 (Tilman et al., 2001, Faostat, 2014). However, the increasing use of N fertilizer in crop production has been identified as a main contributor to the rising levels of atmospheric N2O, which is a long-lasting greenhouse gas that significantly contributes to stratospheric ozone depletion and global climate change (Ravishankara et al., 2009). N2O emission is positively correlated with N application rates in linear or nonlinear relationships in agro-ecosystems (Shcherbak et al., 2014). Consequently, any further increase in N fertilizer application to ensure food security might further stimulate N2O emissions (Popp et al., 2010, Van Beek et al., 2010). Therefore, it is essential to mitigate N2O emission by improving N use efficiency (NUE).

Enhanced-efficiency nitrogen fertilizer (EENF) is designed to reduce potential N loss to the environment and to improve N use efficiency (Halvorson et al., 2014). The main EENF products are slow- or control-releasing fertilizer (S/CRF) and normal N sources treated with nitrification inhibitors (NI) and/or urease inhibitors (UI; Dell et al., 2014). Many reviews (Smith et al., 1997, Oenema et al., 2001, Akiyama et al., 2010, Decock, 2014, Halvorson et al., 2014) and IPCC reports (Smith et al., 2007, Smith et al., 2014) have suggested these products as mitigation options for N2O emission from cropland soils. However, increasing evidence from field experiments showed that the performances of EENF were highly variable across studies. Some studies reported that EENF significantly mitigated N2O emissions compared with normal N fertilizer (Halvorson et al., 2010), and others no significant difference (Chu et al., 2007), or even significantly higher N2O emissions (Hu et al., 2013) with EENF. Furthermore, EENF affects both N2O emission and crop yield. The integrated effect of EENF on N2O emission and crop yield is still uncertain. Reduced N2O emission with either significantly increased (Ma et al., 2013), decreased (Asgedom et al., 2014), or unchanged (Halvorson and Del Grosso, 2013) crop yield has been observed in previous studies. These contradictory results indicate the highly complex nature of the effect of EENF on N2O emission and crop yield.

The mechanisms underlying the effects of EENF on N2O emission are mainly through limiting the substrate pools available for the microbial process of N2O production (Malla et al., 2005, Halvorson et al., 2014). For example, S/CRF can reduce the rate of N release to better match crop uptake; while NI delays the oxidation of ammonia (NH4+) to nitrite (NO2) and then nitrate (NO3); and UI prevents the transformation of urea to NH4+ (Trenkel, 2010). However, these effects on subsurface processes might be affected by climate, soil properties, or agronomical practices. Soil pH might affect the retention time and the effect of NI (Hendrickson and Keeney, 1979, Xue et al., 2012). Meanwhile, agronomical practices might indirectly affect nutrient release from EENF by changing soil properties. For instance, compared with conventional tillage, no-tillage can increase soil bulk density and moisture (De Vita et al., 2007), which in turn may weaken the effect of S/CRF on delay N release from fertilizer. Furthermore, management practices also directly affect N source competition of N2O production and plant uptake by adjusting fertilizer application rates and timings (Drury et al., 2012). Therefore, a better understanding of the impacts of these factors on the effects of EENF will provide good guidelines for the application of EENF in order to mitigate N2O emission with increased crop yield.

Considering the balance of food security and greenhouse gas mitigation, increasing numbers of studies have proposed that an integrated assessment of yield-scaled N2O emission will be particularly important for these practices such as EENF affected both N2O emission and crop yield (Van Groenigen et al., 2010, Linquist et al., 2012, Van Kessel et al., 2013). Many previous studies focused mainly on assessing the effects of EENF on either crop yield or area-scaled N2O emission (Chen et al., 2008, Akiyama et al., 2010, Linquist et al., 2013, Abalos et al., 2014, Qiao et al., 2015, Gilsanz et al., 2016, Yang et al., 2016). The integrated effects of EENF on yield-scaled N2O emission and the corresponding key influencing factors are still unclear. Therefore, a meta-analysis based on peer-reviewed studies was conducted to (i) evaluate the effects of EENF on N2O emissions and agronomic performance, compared with conventional nitrogen fertilizer; (ii) evaluate the impacts of climate (aridity), soil properties (soil pH and texture), fertilizer application strategies (application rate, timing and placement), and soil tillage on the efficacy of EENF.

Section snippets

Data collection

A literature survey of peer-reviewed papers published before March 2015 reporting the results of the effects of EENF on N2O emission was carried out using the ISI-Web of Science and Google Scholar. The literature survey mainly focused on N2O emission from upland cropping systems including maize, wheat, and barley; horticulture crops were excluded. Only studies that met the following criteria were included: (i) the measurements were conducted under field conditions; (ii) N2O flux rate must have

Difference among crops and EENF products

On average, EENF significantly reduced area- and yield-scaled N2O emissions by 25.6% and 26.4%, respectively, compared with conventional N fertilizer. The NUE was significantly enhanced 10.2% by EENF (Fig. 1). No significant difference was found in the effects of EENF on N2O emission and crop yield among the crops of maize, wheat, and barley. However, the effects varied significantly among different EENF products. The IS significantly mitigated area-scaled N2O emission by 31.5% and increased

Study limitations

The EENF has many products, such as DCD (nitrification inhibitor), NBPT (urease inhibitor) and PCF (slow release fertilizer). Their pathway controlling the N releasing and transformation were different from each other. Some previous studies (Abalos et al., 2014, Gilsanz et al., 2016, Yang et al., 2016) have evaluated the efficacy of DCD and DMPP on crop yield or N2O emission under specific soil or management conditions. Besides nitrification inhibitors, this study synthetically analyzed the

Conclusion

This meta-analysis formulated two major generalizations regarding the effects of EENF on N2O emission and crop yield. First, IS showed significant effects on the mitigation of N2O emission and enhancement of crop yield; while S/CRF only significantly reduced N2O emission, its effect on crop yield was not significant. In general, S/CRF was less effective than IS on the mitigation of yield-scaled N2O emission. Second, the effects of IS and S/CRF were highly dependent on climate, soil properties,

Acknowledgement

This work was supported by the Innovation Program of Chinese Academy of Agricultural Sciences, the Special Fund for Agro-scientific Research in the Public Interest (201503116-10), and the State Key Program of China (2016YFD0300803).

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