Can deep tillage enhance carbon sequestration in soils? A meta-analysis towards GHG mitigation and sustainable agricultural management
Introduction
The atmospheric concentration of CO2 is closely coupled with global warming and is increasing at an alarming rate of 4 Pg C per year [1,2]. The overall global soil carbon stock is approximately 2500 Pg, which is about four times the biotic carbon (560 Pg) and about three times the atmospheric one (760 Pg) [3]. Therefore, managing soil carbon proposes an opportunity to offset global CO2 emission [4].
The soil organic carbon (SOC) is estimated to be 615 Pg in the surface layer (measuring to a depth of 0.2 m) and 2344 Pg to a depth of 3 m. Subsoil stores more than 50% of the world's SOC and most of it presents low SOC content [5,6]. SOC turnover in subsoil is limited on account of unfavorable conditions for decomposers, restricted input of fresh organic matter, and low accessibility of decomposers to available SOC [7]. The incorporation of substances rich in SOC into subsoil with a high proportion of undersaturated mineral surface area may help sequester SOC by facilitating the stabilization of buried SOC and limiting SOC decomposition. Nevertheless, subsoil is still poorly understood and neglected constituent of terrestrial carbon pool. For instance, among the 360 studies surveyed focusing on the responses of soil organic matter (SOM) to land management, 90% of them investigated soil depth ≤ 30 cm [8]. The insufficient understanding of deep soil processes may, in turn, lead to misinterpretation of ecological evolution and the underlying processes [9].
SOC is governed by a collection of environmental and management factors and the regulating processes are highly complex. For instance, climatic factors, especially precipitation and temperature, are the most important determinants of SOC contents, due to their impacts on the quantity and quality of residue inputs and the rates of SOM mineralization and litter decomposition [10]. In the context of climate change, for instance, both field measurements and models with respect to climate change predict an incremental trend of drought intensity and frequency [11,12]. Plant development is being confronted with new challenges such as forthcoming supply shortages of water and nutrients. Therefore, it is necessary to provide new access to nutrient and water resources for crops and other plants. The subsoil below the topsoil, which is usually tilled, stores a large amount of nutrients and retains water even under water-restricted circumstance. In fact, it is capable of storing nearly 50% of total nitrogen stocks and 25–70% of total phosphorus stocks [13]. Nevertheless, various factors affect subsoil nutrient availability to plants.
Soil compaction restricts plant root development, impeding the acquisition of resources available in the subsoil, and thereby posing threats to plant productivity and ecological function of the soil [14]. Soil compaction may be caused by (1) large agricultural vehicles used for agricultural production, (2) usage of tillage equipment for many years at the same depth, (3) naturally occurring layers due to soil properties that tend to bind soil particles and eliminate porosity [15], and (4) long-term no tillage (NT) practices [16]. NT farming is widely used in many countries and is one of the most frequently studied agronomic practices for reinforcing carbon sequestration in croplands [[17], [18], [19]]. However, such options have proven to be limited in terms of their ability to mitigate climate change [20,21]. Accumulated SOC as a result of NT has been substantiated to be constrained to easily decomposable component and primarily to the topsoil, which is largely outweighed by subsoil carbon loss [22] and is easily lost by conventional cultivation. Furthermore, long-term NT farming introduces some challenges over years of use, such as herbicide resistance of weeds, proliferation of pests, excessive accumulation of nutrients in the surface soil layer, and soil compaction due to lack of soil mobilization [16]. In this respect, occasional tillage may assist addressing these challenges.
Tillage management, such as cropping intensity, or frequency, also affects SOC storage by disturbing soil and altering the amount of time that the soil is sustaining a crop [23]. DT is a tillage operation performed below the normal tillage depth to break up the plough pan, ameliorate the physical or chemical properties of a soil, alleviate high soil strength, promote deep root development, and facilitate the availability of subsoil resources (Fig. 1). Integrating subsoil in management decisions may provide a means by which for plants to mitigate the adverse effects of soil compaction and climate change, thus sequestrating more carbon. DT has been developed into various types, such as deep ploughing, subsoiling, and deep ripping [24]. The purpose of subsoiling is to loosen soil structure, thereby decreasing subsoil strength without disturbing soil horizons. Subsoiling may also refer to deep ripping or deep chiseling [24]. Deep ploughing, in contrast, disturbs soil horizons, inverses soil profile, and displaces the topsoil, burying it in the deep soil profile [25]. DT has been applied in countries such as Australia [26], China [27,28], Canada [29], Netherlands [30], United States [31], Italy [32], India [33], and Germany [25].
In recent years, several researchers have reported that long-term DT acts as a terrestrial carbon sink in the context of rising concerns over atmospheric CO2 emission. For instance, Schiedung et al. [34] reported that SOC stocks in the depth of 0–150 cm increased by 69% over 20 years after deep flipping in the pasture in New Zealand. Alcantara et al. [35] demonstrated that deep-ploughed soil comprised mean 42% more SOC than the reference soil after 45 years. However, some studies have revealed that tillage may accelerate the fragmentation of soil aggregates which is a major protection for SOC, thus increasing the possibility of organic matter mineralization and acting as a carbon source for atmospheric carbon pool [36]. Meanwhile, the extent to which DT as a regular tillage practice contributes to SOC sequestration under different environmental and management conditions is not well understood and merits further exploration. In this context, the objectives of this project are to (1) obtain a quantitative review of published DT impacts on SOC stock; and (2) identify the role of environmental variables and management practices in constraining SOC stock response to DT.
Section snippets
Data sources
A detailed review of the literature published in peer-reviewed journals for all years up to December 2019 was conducted. Publications were searched from Web of Science using the search terms shown in Table 1.
The following criteria were fulfilled: (1) article compared the SOC content or stocks of ordinary-tilled plot (control treatment, CT) with adjacent deep tillage plot (DT) based on field study; (2) DT and CT received similar agronomic treatments apart from tillage depth, and only studies
General dataset information
After the screening process, a total of 43 publications (from 1987 to 2019) covering 43 field experimental sites and representing 430 observations were selected (Table S1). The distribution of field experimental sites is shown in Fig. 2. Overall, the effect size of SOC under DT was found to exhibit a normal distribution (Fig. 3). The fail-safe number for publication bias analysis is 45,508, indicating that most of the results considered in this study were robust (Table S2).
The database was
The effects of DT on SOC
Soil carbon are mainly from: (1) accumulation of SOC due to the humification of plant residues and (2) root-borne substances and root exudates released into the rhizosphere during plant growth and root sloughing [52]. DT can be an effective tool for treating soil with physical barriers in order to loosen soil structure, alleviate high soil strength, and promote deep root development. In soils, the transformation of organic residues into recalcitrant substances is crucial to carbon
Conclusions
The effects of DT practice on SOC were assessed using meta-analysis in this study. In general, DT significantly enhanced SOC compared to CT. Specifically, deep ploughing was found to benefit subsoil carbon sequestration (20–50 cm), although it may depress surface SOC content. The SOC change rate at the subsoil (30–50 cm) was significantly negative relative to the SOC of topsoil (0–10 cm) under deep ploughing. It was found that, subsoiling, in contrast, did not carry this risk. The enhancement
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 research was supported by the Natural Sciences and Engineering Research Council of Canada. The authors are thankful for the comments and suggestions from Jonathan Tomalty, the editor and the anonymous reviewers.
References (153)
- et al.
The effect of introducing a winter forage rotation on CO2 fluxes at a temperate grassland
Agric Ecosyst Environ
(2012) - et al.
Global heat stress on health, wildfires, and agricultural crops under different levels of climate warming
Environ Int
(2019) - et al.
Nutrient acquisition from arable subsoils in temperate climates: a review
Soil Biol Biochem
(2013) - et al.
No-tillage and soil physical environment
Geoderma
(2018) - et al.
Greenhouse gas emissions and crop yield in no-tillage systems: a meta-analysis
Agric Ecosyst Environ
(2018) - et al.
Soil macroaggregate turnover and microaggregate formation: a mechanism for C sequestration under no-tillage agriculture
Soil Biol Biochem
(2000) - et al.
The effect of no-till on organic C storage in Chinese soils should not be overemphasized: a meta-analysis
Agric Ecosyst Environ
(2017) - et al.
The effect of deep tillage on crop yield – what do we really know?
Soil Tillage Res
(2017) Effects of deep ripping, direct drilling, gypsum and lime on soils, wheat growth and yield
Soil Tillage Res
(1986)- et al.
Subsoiling and ridge tillage alleviate the high temperature stress in spring maize in the North China Plain
J Integr Agric
(2013)
Experiences with deep tillage in The Netherlands
Soil Tillage Res
Tillage choices affect biochemical properties in the soil profile
Soil Tillage Res
Tillage affects soil aggregation parameters linked with wind erosion
Geoderma
Effects of different tillage practices on the carbon footprint of wheat and maize production in the Loess Plateau of China
J Clean Prod
Effects of different sub-soiling frequencies incorporated into no-tillage systems on soil properties and crop yield in dryland wheat-maize rotation system
Field Crop Res
Global synthesis of drought effects on cereal, legume, tuber and root crops production: a review
Agric Water Manag
Ranking yields of energy crops: a meta-analysis using direct and indirect comparisons
Renew Sustain Energy Rev
Influences of nitrogen fertilization and climate regime on the above-ground biomass yields of miscanthus and switchgrass: a meta-analysis
Renew Sustain Energy Rev
Roots contribute more to refractory soil organic matter than above-ground crop residues, as revealed by a long-term field experiment
Agric Ecosyst Environ
Soil wet aggregate distribution and pore size distribution under different tillage systems after 16 years in the Loess Plateau of China
Catena
Deep soil water extraction by apple sequesters organic carbon via root biomass rather than altering soil organic carbon content
Sci Total Environ
Impact of soil movement on carbon sequestration in agricultural ecosystems
Environ Pollut
Effects of organic matter on the physical and the physicochemical properties of an illitic soil
Appl Clay Sci
Restoration of eroded soil with conservation tillage
Soil Technol
Soil aggregation, aggregate stability, organic carbon and nitrogen in different soil aggregate fractions under forest and shrub vegetation on the Loess Plateau, China
Catena
Change of soil physical properties under long-term natural vegetation restoration in the Loess Plateau of China
J Arid Environ
Subsoiling improves soil physical and microbial properties, and increases yield of winter wheat in the Huang-Huai-Hai Plain of China
Soil Tillage Res
Long-term effects of tillage, cover crops, and nitrogen fertilization on organic carbon and nitrogen concentrations in sandy loam soils in Georgia, USA
Soil Tillage Res
Artificial macropores attract crop roots and enhance plant productivity on compacted soils
Sci Total Environ
Vulnerability of subsoils in Europe to compaction: a preliminary analysis
Soil Tillage Res
Organic geochemical studies of soils from the Rothamsted Classical Experiments—IV. Preliminary results from a study of the effect of soil pH on organic matter decay
Org Geochem
pH regulation of carbon and nitrogen dynamics in two agricultural soils
Soil Biol Biochem
Effect of annual variation in soil pH on available soil nutrients in pear orchards
Acta Ecol Sin
The carbon cycle and atmospheric carbon dioxide
Fine resolution carbon dioxide emission gridded data and their application for China
J Environ Inform
Carbon sequestration
Phil. Trans. R. Soc. B
Climate-smart soils
Nature
The vertical distribution of soil organic carbon and its relation to climate and vegetation
Ecol Appl
Stability of organic carbon in deep soil layers controlled by fresh carbon supply
Nature
One physical system: tansley's ecosystem as Earth's critical zone, Tansley review
New Phytol
Understanding deep roots and their functions in ecosystems: an advocacy for more unconventional research
Ann Bot
Soil carbon and nitrogen changes following afforestation of marginal cropland across a precipitation gradient in Loess Plateau of China
PloS One
Drought under global warming: a review
Wiley Interdiscip Rev Clim Change
Soil compaction effects on soil health and cropproductivity: an overview
Environ Sci Pollut Res
A review and suggestions for reducing cost of this conservation tillage operation
Appl Eng Agric
Methane and nitrous oxide emissions under no-till farming in China: a meta-analysis
Global Change Biol
Limited potential of no-till agriculture for climate change mitigation
Nat Clim Change
Impact of tillage intensity on carbon and nitrogen pools in surface and sub-surface soils of three long-term field experiments
Eur J Soil Sci
How does tillage intensity affect soil organic carbon? A systematic review
Environ Evid
The ‘invisible’ subsoil: an exploratory view of societal acceptance of subsoil management in Germany
Sustainability
Cited by (63)
Soil nitrogen availability mediates the positive effects of intercropping on soil organic carbon at global scales
2024, Soil and Tillage ResearchRoot-derived carbon stocks in formerly deep-ploughed soils – A biomarker-based approach
2024, Organic GeochemistryMicrobial carbon capture - evolving trends, interconnections, and recent spotlights of the past three decades
2024, Chemical Engineering JournalCarbon trade-off and energy budgeting under conventional and conservation tillage in a rice-wheat double cropping system
2024, Journal of Environmental ManagementAn insight into the benefits of substituting polypropylene with biodegradable polylactic acid face masks for combating environmental emissions
2023, Science of the Total Environment