Elsevier

Agriculture, Ecosystems & Environment

Volume 213, 25 December 2015, Pages 241-251
Agriculture, Ecosystems & Environment

Nitrous oxide emissions from an agro-pastoral ecotone of northern China depending on land uses

https://doi.org/10.1016/j.agee.2015.08.011Get rights and content

Highlights

  • The spring–thaw N2O pulses dominated the annual emission.

  • Soil mineral N contents explained 80% of N2O flux variability during spring thaw.

  • Grazing reduced annual N2O emissions.

  • Conversion from grassland to cropland increased N2O flux.

Abstract

Overgrazing and intensive farming have led to severe land degradation in the past half century in the agro-pastoral ecotone of northern China. Currently, complete and periodical exclusions of grazing are commonly adopted for the restoration of these degraded grasslands. However, little is known about the effects of such land uses on nitrous oxide (N2O) emission in this region. Using static chamber technique, we quantified annual N2O emissions (from May 2012 to September 2013) from four land uses: summer-grazed grassland (SG), winter-grazed grassland (WG), ungrazed grassland since 1997 (UG) and oat cropland (OC). N2O emissions occurred mainly after farmyard manure fertilization and during spring thaw periods. Annual N2O fluxes from the SG, WG, UG and OC were 0.19, 0.15, 0.43 and 0.98 kg N ha−1 yr−1, respectively. The spring–thaw N2O emissions from UG and OC dominated the annual emission and accounted for 70% and 65% of the annual fluxes, respectively. In contrast, the contributions of spring thaw fluxes to total annual N2O emissions for SG and WG were only 32%. N2O fluxes during spring thaw season were positively related to soil NH4+ +  NO3 content accounting for 80% of N2O flux variability across all land uses. Land use conversion from the native grassland to cropland increased N2O flux both during growing and spring thaw seasons due to farmyard manure application. Instead, grazing has the potential to decrease annual N2O losses mainly through reducing spring–thaw N2O emissions.

Introduction

Nitrous oxide (N2O) is one of the important greenhouse gases with a global warming potential 265 times that of CO2 and an atmospheric lifetime of about 121 years (IPCC, 2013). Moreover, N2O plays a role in the destruction of ozone in the stratosphere. In viewed of atmospheric N2O concentration increase of about 0.3% per year, it can be expected that the contribution of N2O to global warming will further increase in the future (Wu et al., 2010). Soils are the dominant source of N2O worldwide, releasing an estimated 9.5 Tg N yr−1 to the atmosphere (65% of global N2O emissions), of which 3.5 Tg N yr−1 originate in agricultural soils and 1 Tg N yr−1 in temperate grasslands (Flechard et al., 2007).

Land use change is one of the major factors regulating soil N2O emission (Skiba and Smith, 2000). Crop cultivation and grazing, main land uses, could profoundly impact N2O emissions of grassland ecosystem through altering abiotic and biotic characteristics of soil (Holst et al., 2007, Mosier et al., 1997, Rafique et al., 2011, Ri et al., 2003). It has been generally recognized that conversion of grassland to croplands increases the emission of N2O due to the impacts of agricultural practices, especially organic and mineral nitrogen (N) fertilization (Mosier et al., 1997, Wang et al., 2001). However, effects of grazing on N2O emissions still remain controversial, with increases (Rafique et al., 2011, Saggar et al., 2007), decreases (Wolf et al., 2010, Xu et al., 2008), and no changes (Holst et al., 2007, Li et al., 2012) all being reported. The discrepancies between studies could be attributable to different grazing history, grassland type, climate regime and type of soil. Therefore, it is important to investigate N2O emissions under site-specific land use patterns in order to draw regionally specific conclusions.

Although N2O emissions from grasslands have been investigated worldwide, there are still high uncertainties in estimates of annual soil-atmosphere N2O exchange of grassland ecosystem because most investigations have focused on the growing season (Holst et al., 2007, Xu et al., 2008). Several studies have revealed that winter or spring–thaw N2O loss can be of major importance for the annual N2O loss in temperate ecosystems (Röver et al., 1998, Teepe et al., 2000, Wagner-Riddle et al., 2007, Wolf et al., 2010). In some cases up to 80% of the annual N2O emissions were found in the spring–thaw period (Holst et al., 2008, Wolf et al., 2010). This phenomenon has been attributed to physical release of N2O produced in unfrozen part of the soil and accumulated below the frozen soil layer (Burton and Beauchamp, 1994, Teepe et al., 2001) and/or enhanced microbial metabolism by substrate supply (Röver et al., 1998, Wolf et al., 2010). Moreover, the magnitude of spring–thaw N2O emission may differ between land uses even at similar weather (Holst et al., 2008, Wagner-Riddle and Thurtell, 1998, Wolf et al., 2010). Clearly, long-term studies of at least one year or more are necessary for reliable estimates of annual N2O release from soil.

The agro-pastoral ecotone in northern China covers 6.2 × 105 km2 from the North China Plain to the Inner Mongolia Plateau (Liu and Gao, 2008). It is a transitional land use from livestock-grazing to farming in between semi-arid temperate steppe and semi-humid cropland. This region plays an important role in livestock farming and environmental conservation. However, overgrazing and intensive farming have led to severe land degradation in the past half century in this region. Currently, improved grassland management practices, complete and periodical exclusions of grazing are commonly adopted for the restoration of these degraded grasslands. Quantifying the effects of cultivation and grazing regimes on the greenhouse gas emissions is critical for the understanding of consequences of land use conversion including that on N2O emissions. However, previous studies of N2O emissions in the semi-arid grassland in China have primarily focused on the growing season (Holst et al., 2007, Xu et al., 2008) and on grazing management (Wolf et al., 2010). Limited evaluations of annual N2O emissions and land uses including both cropland and grassland underscore the need for additional research.

In present study, we measured soil N2O emissions, temperature, soil moisture and mineral N content (NH4+ + NO3) over a 16-month period from four land uses in the agro-pastoral zone of northern China. The objectives were to: (1) investigate seasonal variations of N2O fluxes depending on land uses; (2) quantify annual N2O emissions depending on land uses and evaluate the contribution of spring–thaw N2O emissions to annual N2O losses; (3) examine the effects of soil temperature, water-filled pore space (WFPS) and mineral N content (NH4+ + NO3) on N2O fluxes from land uses.

Section snippets

Study site

The study was carried out at the National Grassland Ecosystem Observation and Research Station (41°46′N, 115°40′E, 1460 m above sea level), which lies in the typical agro-pastoral ecotone in the Guyuan county, Hebei province, Northern China. The region has a semi-arid and temperate continental monsoon climate, with a frost-free period of 80–110 days. The 30 year (1979–2009) annual mean precipitation is 380 mm with 80% falling during the growing season from May to September. The annual mean

Environmental variables

During the period studied (from May 2012 to September 2013), the mean daily air temperature ranged from −32.1 °C (6 February 2013) to 23.6 °C (23 June 2013) with a mean of 2.8 °C (Fig. 1). Total precipitation for the sampling period was 654 mm (Fig. 2, Fig. 3, Fig. 4, Fig. 5b). From October 2012 to September 2013, the annual mean air temperature (−1.7 °C) was lower than the 30-year average of 1.4 °C, while annual precipitation (415 mm) was greater than the long time average of 380 mm. Precipitation

Annual N2O emissions

The annual N2O emissions from three grassland sites ranged from 0.15 to 0.43 kg N ha−1 yr−1 (Table 2), indicating that the investigated grassland soils functioned as a source of atmospheric N2O. On average, grassland soils released about 0.25 kg N ha−1 yr−1 (arithmetic average of three sites) into the atmosphere. The annual N2O emissions observed here were within the range of emissions observed from temperate semi-arid grassland (0.01–0.73 kg N ha−1 yr−1) in Inner Mongolia (Du et al., 2006, Wang et al.,

Conclusions

We quantified annual N2O emissions depending on land uses in a semi-arid agro-pastoral ecotone of northern China. Emissions of N2O occurred mainly after farmyard manure fertilization and during spring thaw periods. The spring–thaw N2O pulses dominated the annual emission for UG and OC, whereas only one third of the annual N2O emission for SG and WG. Our results stressed the importance of spring–thaw N2O losses for the annual balance. Conversion from grassland to cropland increased N2O flux both

Acknowledgements

This study was funded by Non-profit Research Foundation for Agriculture (201103039), National Natural Science Foundation of China (40801108, 40425007), National Basic Research Program of China (973 Program) (2009CB118607), Chinese Universities Scientific Fund (2012QJ092).

References (54)

  • U. Skiba et al.

    The control of nitrous oxide emissions from agricultural and natural soils

    Chemosphere Glob. Change Sci.

    (2000)
  • K.A. Smith et al.

    Effects of temperature, water content and nitrogen fertilisation on emissions of nitrous oxide by soils

    Atmos. Environ.

    (1998)
  • R. Teepe et al.

    Nitrous oxide emissions from frozen soils under agricultural, fallow and forest land

    Soil Biol. Biochem.

    (2000)
  • R. Teepe et al.

    Nitrous oxide emissions from soil during freezing and thawing periods

    Soil Biol. Biochem.

    (2001)
  • K. Wang et al.

    Comparison between static chamber and tunable diode laser-based eddy covariance techniques for measuring nitrous oxide fluxes from a cotton field

    Agric. For. Meteorol.

    (2013)
  • Y.S. Wang et al.

    Effects of environmental factors on N2O emission from and CH4 uptake by the typical grasslands in the Inner Mongolia

    Chemosphere

    (2005)
  • G.X. Yan et al.

    Two-year simultaneous records of N2O and NO fluxes from a farmed cropland in the northern China plain with a reduced nitrogen addition rate by one-third

    Agric. Ecosyst. Environ.

    (2013)
  • J.F. Zhang et al.

    N2O emission from the semi-arid ecosystem under mineral fertilizer (urea and superphosphate) and increased precipitation in northern China

    Atmos. Environ.

    (2008)
  • F. Barker-Reid et al.

    Soil nitrous oxide emission from rainfed wheat in SE Australia

  • L. Barton et al.

    Nitrous oxide emissions from a cropped soil in a semi-arid climate

    Glob. Change Biol.

    (2008)
  • G.R. Blake et al.

    Bulk density

  • M. Burger et al.

    Microbial responses and nitrous oxide emissions during wetting and drying of organically and conventionally managed soil under tomatoes

    Biol. Fertil. Soils

    (2005)
  • D.L. Burton et al.

    Profile nitrous oxide and carbon dioxide concentrations in a soil subject to freezing

    Soil Sci. Soc. Am. J.

    (1994)
  • M.D. Corre et al.

    Estimation of annual nitrous oxide emissions from a transitional grassland–forest region in Saskatchewan, Canada

    Biogeochemistry

    (1999)
  • E.A. Davidson

    Sources of nitric oxide and nitrous oxide following wetting of dry soil

    Soil Sci. Soc. Am. J.

    (1992)
  • A. del Prado et al.

    N2O and NO emissions from different N sources and under a range of soil water contents

    Nutr. Cycl. Agroecosyst.

    (2006)
  • K.E. Dobbie et al.

    Nitrous oxide emission factors for agricultural soils in Great Britain: the impact of soil water-filled pore space and other controlling variables

    Glob. Change Biol.

    (2003)
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