Elsevier

Geoderma

Volume 420, 15 August 2022, 115896
Geoderma

Determining the hot spots and hot moments of soil N2O emissions and mineral N leaching in a mixed landscape under subtropical monsoon climatic conditions

https://doi.org/10.1016/j.geoderma.2022.115896Get rights and content

Highlights

  • The hot spots of N2O emissions and N leaching were distributed in the tea garden.

  • Temperature, precipitation and fertilization triggered the hot moments of N losses.

  • Land-use type was the primary factor for the hot spots formation of N losses.

  • Topography and soil properties also affected the hot spots formation of N losses.

Abstract

Identification of hot spots and hot moments (HSHMs) in regard to soil nitrogen (N) losses has received public attention. Soil nitrous oxide (N2O) emissions and mineral N leaching under varied annual precipitation were simulated with the DayCent model in a mixed landscape (tea garden, bamboo forest and coniferous and broad-leaved mixed forests). Their HSHMs were further quantified using the 3rd quartile value of all data as the baseline. Results showed that the hot moments of soil N2O emissions were the dry year, summer, and months with high air temperature (July to September) and months after fertilization (April or May) at inter-annual, seasonal and monthly time scales, respectively. The hot moments of mineral N leaching at these time scales were the normal year or the wet year, spring or rainy seasons after drought, and rainy months after fertilization or drought, respectively. The main factors controlling the formation of hot moments on N losses were temperature, precipitation and fertilization. In addition, the hot spots of N2O emissions and mineral N leaching in the mixed landscape were both distributed in the tea garden (TG). When the entire study area was assumed to be under the same land-use type (i.e., TG), the hot spots of these two kinds of N losses were mainly distributed in the areas with rock fragment content < 0.16 cm3 cm−3, field capacity > 0.24 cm3 cm−3, bulk density > 1.29 g cm−3, soil carbon (C)/N ratio < 13.26, and slope < 12°. These results indicated that fertilizer management, climate factors, soil properties and topography need to be comprehensively considered to alleviate the formation of HSHMs of N losses in mixed landscape mountainous areas.

Introduction

Soil nitrous oxide (N2O) emissions and mineral nitrogen (N) leaching act as two main pathways of soil N losses (Fowler et al., 2013). Soil N2O emissions, which are mainly driven by microbial processes (e.g., nitrification and denitrification), could cause global warming and ozone depletion (Erisman et al., 2013, Ussiri and Lal, 2013). Excessive mineral N leaches into the ground and surface water, which could decrease the quality of water bodies and potentially promote the eutrophication (Sinha et al., 2017). Disproportionately high N2O emissions or mineral N leaching occur as localized areas (hot spots) relative to the surrounding matrix or during short periods (hot moments) relative to longer intervening time periods (Bernhardt et al., 2017), which have been observed at the field and watershed scales (Kurunc et al., 2011, Weitzman et al., 2021). Therefore, it is necessary to reveal the mechanisms of HSHMs on these two reactive N loss pathways to provide effective mitigation strategies (Krichels and Yang, 2019, Palta et al., 2014).

The hot moments of soil N2O emissions and mineral N leaching are influenced by multiple factors, e.g., climate factors, vegetation growth, and management practices (Molodovskaya et al., 2012, Wagner-Riddle et al., 2020, Zhu et al., 2012). For example, abundant precipitation increases water input, which may form a short-term anaerobic state, inhibit nitrification, promote denitrification, and even induce water flows that leach N (Blaen et al., 2017). Warming may promote soil respiration and microbial activity, strengthening microbial processes (Dai et al., 2020). As plants grow, plant uptake of N changes the availability of soil N for microbial or leaching processes (de Vries and Bardgett, 2012). Plant evapotranspiration rates affect soil water content (SWC), controlling the denitrification rate (Krichels and Yang, 2019). Land management practices, especially fertilization, aggravate mineral N input (Eagle et al., 2017). Meanwhile, tillage, irrigation or cover cropping influence the availability of organic carbon (C), N, oxygen and water, regulating soil N losses (Quemada et al., 2013, Thapa et al., 2018, Yangjin et al., 2021). However, controlling factors of hot moments are controversial among regions or land-use types. For instance, hot moments of N2O emissions have been observed during heavy precipitation under warm conditions in soybean field (Krichels and Yang, 2019), or during summer precipitation and spring thaw in corn field, enhanced by fertilization (Molodovskaya et al., 2012). Hot moments of N leaching in forestland or cropland have been during the non-growing season (Zhu et al. 2012). Influencing factors of hot moments of N losses are complex, so further research is needed to reveal them in mixed landscape areas.

The hot spots of soil N2O emissions and mineral N leaching are influenced by soil properties and vary with topography and land-use type (Kurunc et al., 2011, Parn et al., 2018, Wagner-Riddle et al., 2020). For instance, rock fragment content (RFC) changes the hydraulic conductivity and volume of fine-soil matrix, regulating soil environment and solute transportation (Hlaváčiková et al., 2015). Low relative gas diffusion rates in high bulk density (BD) soils diminish gas diffusion, which may generate anaerobic conditions (Balaine et al., 2013). The SWC controls the gas diffusion rate and microbial activity and changes redox conditions and thus N availability (Parn et al., 2018). Texture affects soil pore space and water-holding capacity, regulating subsurface flows and rates of microbial processes (Palta et al., 2014). Soil C/N ratio and organic matter content provide the C and N substrates for microbial processes and change the cation exchange capacity and soil structure (Figueiredo et al., 2016, Gundersen et al., 2012). Topographic factors, e.g., slope and elevation, influence soil hydrology and spatial distribution of soil properties (Lai et al., 2018a, Pennock et al., 2010). Land-use type regulates soil properties by plant attributes (e.g., plant N uptake and evapotranspiration) and affects N input with management practices (Abalos et al., 2016, Palmer et al., 2014). However, controlling factors of hot spots vary with the sampling period. For example, hot spots of N2O emissions have been located in areas of low slope and elevation after fertilization (Turner et al., 2016), while topographic depressions have not triggered them during the soybean-growing season (Krichels and Yang, 2019). Hot spots of N leaching in farmland during May to June have coincided with low water-holding capacity and heavy irrigation (Kurunc et al., 2011). Therefore, factors affecting hot spots of N losses have to be further identified at longer time scales (e.g., annual).

Tea plant (Camellia sinensis (L.) O. Kuntze) has rapidly expanded to 66 kha yr−1 by destroying forestlands (Han et al., 2021), aggravating the possibility of soil N2O emissions and eutrophication of water bodies (Chen et al., 2019a, Wang et al., 2020). Therefore, this paper used the DayCent model to simulate N2O emissions and mineral N leaching under different precipitation years in a mixed landscape. The objective of this study was to identify hot moments and hot spots of these two N losses and reveal their main controlling factors. We hypothesized that their hot moments were controlled by climate factors and land management (e.g., fertilization), while hot spots were primarily affected by land-use type, assisted by soil properties and topography.

Section snippets

Study site

Qing Hill (31°20.72′-31°23.33′N, 119°2.42′-119°4.48′E) has an area of 747.33 ha, and is located in the northwestern hilly region of Taihu Lake Basin, China (Fig. 1). It has a subtropical monsoon climate with the mean annual air temperature and precipitation of 15.9℃ and 1157 mm over 60 years, respectively. The primary land-use types are TG, bamboo forest or BF (Phyllostachys edulis (Carr.) H. de Lehaie), and coniferous and broad-leaved mixed forests (MFs). The MFs contain Masson pine (Pinus

Environmental conditions and model performances

The climate factors varied significantly (P < 0.05) among years, and the representatively spatial factors were significantly (P < 0.05) associated with N2O emissions and mineral N leaching (Figs. S1 and 2). Compared with the NY, the precipitation amount during the DY decreased in summer and fall, while that during the WY increased in spring and fall. The DY had higher mean annual air temperature (17.79℃) than the NY and WY. The representatively spatial factors included soil BD (ranging from

Controlling factors of hot moments

Temperature rather than precipitation was closely associated with soil N2O emissions, which was a positive relationship (Figs. S2 ∼ S3, Table 2). Hot moments of N2O emissions appeared in months or seasons with high air temperatures, which were similar to other ecosystems, e.g., tea fields and Masson pine forests (Chen et al., 2019a), grasslands and cornfields (Li et al., 2015), and cropland with alfalfa and corn (Molodovskaya et al., 2012). This may be attributed to the fact that high

Conclusions

Based on the DayCent simulation, the HSHMs of soil N2O emissions and mineral N leaching were identified using the quantification method in hilly mountain areas. Hot moments of N2O emissions at inter-annual, seasonal, and monthly time scales included the DY, the summer, and the months with high temperature (July to September) and months after fertilization (April or May), respectively. Hot moments of mineral N leaching across these time scales, were the NY or WY, spring or rainy season after

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This study was financially supported by the National Natural Science Foundation of China (42125103 and 42171077), the China Postdoctoral Science Foundation (2021M692145), and the Youth Innovation Promotion Association, Chinese Academy of Sciences (2020317 and 2019313).

References (58)

  • M.J. Li et al.

    Evaluation of N2O and CO2 hot moments in managed grassland and cornfield, southern Hokkaido, Japan

    Catena

    (2015)
  • S.D. Logsdon et al.

    Soil nutrient variability and groundwater nitrate-N in agricultural fields

    Sci. Total Environ.

    (2018)
  • S. Molina-Herrera et al.

    A modeling study on mitigation of N2O emissions and NO3 leaching at different agricultural sites across Europe using LandscapeDNDC

    Sci. Total Environ.

    (2016)
  • R.H. Patil et al.

    Effect of soil warming and rainfall patterns on soil N cycling in Northern Europe

    Agric. Ecosyst. Environ.

    (2010)
  • D. Pennock et al.

    Landscape controls on N2O and CH4 emissions from freshwater mineral soil wetlands of the Canadian Prairie Pothole region

    Geoderma

    (2010)
  • A. Perego et al.

    Nitrate leaching under maize cropping systems in Po Valley (Italy)

    Agric. Ecosyst. Environ.

    (2012)
  • M. Quemada et al.

    Meta-analysis of strategies to control nitrate leaching in irrigated agricultural systems and their effects on crop yield

    Agric. Ecosyst. Environ.

    (2013)
  • M.G. Schaap et al.

    ROSETTA: a computer program for estimating soil hydraulic parameters with hierarchical pedotransfer functions

    J. Hydrol.

    (2001)
  • F. Sekucia et al.

    Land-use impact on porosity and water retention of soils rich in rock fragments

    Catena

    (2020)
  • P.A. Turner et al.

    A geostatistical approach to identify and mitigate agricultural nitrous oxide emission hotspots

    Sci. Total Environ.

    (2016)
  • C. Wagner-Riddle et al.

    Mitigation of nitrous oxide emissions in the context of nitrogen loss reduction from agroecosystems: managing hot spots and hot moments

    Curr. Opin. Environ. Sustain.

    (2020)
  • D.Z. Yangjin et al.

    A meta-analysis of management practices for simultaneously mitigating N2O and NO emissions from agricultural soils

    Soil Tillage Res.

    (2021)
  • Q. Zhu et al.

    Soil moisture response to rainfall at different topographic positions along a mixed land-use hillslope

    Catena

    (2014)
  • Q. Zhu et al.

    Hot moments and hot spots of nutrient losses from a mixed land use watershed

    J. Hydrol.

    (2012)
  • T.B. Zhu et al.

    Tea plantation destroys soil retention of NO3- and increases N2O emissions in subtropical China

    Soil Biol. Biochem.

    (2014)
  • D. Abalos et al.

    Micrometeorological measurements over 3 years reveal differences in N2O emissions between annual and perennial crops

    Glob. Change Biol.

    (2016)
  • N. Balaine et al.

    Changes in relative gas diffusivity explain soil nitrous oxide flux dynamics

    Soil Sci. Soc. Am. J.

    (2013)
  • E.S. Bernhardt et al.

    Control points in ecosystems: moving beyond the hot spot hot moment concept

    Ecosystems

    (2017)
  • P.J. Blaen et al.

    High-frequency monitoring of catchment nutrient exports reveals highly variable storm event responses and dynamic source zone activation

    J. Geophys. Res.-Biogeosci.

    (2017)
  • Cited by (0)

    View full text