Short-term influence of tillage on CO2 fluxes from a semi-arid soil on the Canadian Prairies

doi:10.1016/S0167-1987(98)00188-3

Soil and Tillage Research

Volume 50, Issue 1, 15 February 1999, Pages 21-32

https://doi.org/10.1016/S0167-1987(98)00188-3 Get rights and content

Abstract

The flux of CO₂ from soil determines the extent to which carbon (C) deposited as plant litter is retained in the soil. Retention of soil C is beneficial for soil physical, chemical and biological properties, and is essential if soils are to be used as a repository of C to mitigate atmospheric CO₂ increases. Although tillage is assumed to have a major influence on soil C retention, the extent to which tillage enhances the transfer of soil C to the atmosphere is uncertain. We assessed the short-term (50 h) influence of tillage on CO₂ fluxes from Chernozemic soils under a two-year wheat (Triticum aestivum L.)-summerfallow rotation in a semi-arid region of the Canadian Prairie. The tillage effect and its persistence were assessed by using a portable CO₂ analyzer to record several temporal series of CO₂ fluxes, along undisturbed and tilled transects, at successive time intervals (from −0.5 to 50 h) after a single pass with a heavy-duty cultivator. Immediately after tillage, CO₂ fluxes along the tilled transects increased from 2 to 4-fold above pre-tillage fluxes, but the increases were short-lived and fluxes along undisturbed and tilled transects were again similar within 24 h of cultivation. Total amounts of CO₂ released by a tillage operation were quantified by:

1.
linear interpolations among successive fluxes along tilled and undisturbed transects, and
2.
by fitting a model to successive differences between fluxes along the transects.

Both methods estimated the amounts of tillage-susceptible CO₂ to be in the range of 3.6–7.2 kg C ha⁻¹. The tillage-induced flush of CO₂ was attributed mainly to enhanced transport of CO₂ already in the soil, but enhanced production of CO₂ by heterotrophic soil organisms also may have contributed to the flush. Regardless of the sources of CO₂ released by single tillage operations, amounts of tillage-susceptible soil C were minor; even 10 passes with a cultivator would account for less than 5% of annual soil CO₂ emissions or crop residue production in these cropping systems. Our study suggested that the short-term influence of tillage on the transfer of soil C to atmospheric CO₂ is small under semi-arid conditions like those in southern Alberta, Canada.

Introduction

The flux of CO₂ from soils to the atmosphere (soil respiration) determines the extent to which plant C added to the soil is retained or released to the atmosphere. Retention of soil C is important, because soil organic matter is a nutrient reservoir for plants, a binding agent for soil structure, and a major carbon pool which may serve as a repository of C to mitigate atmospheric CO₂ increases. Soil CO₂ fluxes are strongly dependent on plant and soil microbial growth as influenced by temperature and moisture. They may also be sensitive to management, including selection of crop species, tillage, and addition of fertilizers and manure. Information on the influence of management on soil CO₂ fluxes is required to identify practices that maintain soil productivity and retard the conversion of soil C to atmospheric CO₂.

Tillage practices may have a measurable influence on soil C storage after 5–40 years (Campbell et al., 1995; Larney et al., 1997), and conservation tillage has been proposed as a means to increase sequestration of soil C (Kern and Johnson, 1993). Apart from the increased susceptibility of tilled soils to erosion (lateral redistribution of soil C), the mechanisms of tillage-induced decreases in soil organic matter are uncertain. While measurement of change in soil C storage over extended periods indicates the long-term influence of tillage, short-term estimates of CO₂ fluxes may provide more information on the mechanisms involved. Tillage-induced changes in soil C storage (if any) may reflect both the immediate (within 7 d) influence of tillage operations on CO₂ fluxes, and the longer-term influence of tillage on the decomposition environment (e.g., moisture, temperature, residue surface area, and microbial accessibility).

Seasonal monitoring of CO₂ fluxes from soils under contrasting tillage regimes suggests that similar amounts of CO₂ are emitted from no-tillage and conventionally tilled systems. Hendrix et al. (1988)reported that fluxes were slightly greater in no-tillage plots than in conventionally tilled plots in Georgia, contrary to their expectation that tillage would stimulate CO₂ efflux. Similarly, Franzluebbers et al., 1995a, Franzluebbers et al., 1995breported that annual soil CO₂ fluxes from various cropping systems in Texas were not significantly different or up to 23% greater in no-tillage compared to conventionally disked systems. Since fluxes were measured 5 years after tillage treatments were imposed in the Georgia study and 9 years after in the Texas studies, the initial response of CO₂ emissions to tillage may have been missed. Fortin et al. (1996)monitored CO₂ fluxes immediately after tillage treatments were imposed on barley in Ontario, and observed that mean fluxes during the first growing season were lower under no-tillage compared to conventional tillage, but during the following year mean fluxes under the contrasting tillage systems were similar.

Soil CO₂ evolution must decrease if C sequestration is to be enhanced without increasing C inputs. The lack of appreciable tillage-induced differences in seasonal CO₂ efflux suggests that tillage effects may be relatively minor or obscured by variability, or that measurement schedules to quantify seasonal CO₂ efflux fail to capture large but fleeting fluxes associated with episodic tillage operations. Soil disturbance by tillage has been observed to increase CO₂ fluxes in the short-term (e.g., Seto, 1982), but the immediate contribution of soil disturbance to CO₂ efflux has not been adequately quantified. Seto (1982)observed that soil CO₂ fluxes increased over 4-fold after plowing, and that the high rates persisted for 3 d before returning to those observed before plowing. Reicosky and Lindstrom (1993)observed that various tillage methods increased both short-term (4.5 d) and intermediate-term (19 d) fluxes of soil CO₂, and that the increases were related to tillage intensity and surface roughness.

The objective of this study is to quantify the short-term influence of single tillage operations on fluxes of soil CO₂ from semi-arid cropland.

Section snippets

Site description

This study was conducted on loam-textured, moderately calcareous, Dark Brown Chernozemic (USDA: Typic Haploboroll; FAO: Typic Kastanozem) soils developed under mixed grass prairie on lacustrine parent materials. The soils, at Lethbridge, Canada, had been converted from native grassland in the early 1900s, and currently are cropped under a spring wheat-fallow rotation. Lethbridge is located in a semi-arid region with mean annual precipitation of 400 mm (70% as rain from April to September), pan

CO₂ fluxes within 6 h of tillage (17 and 31 May 1994 series cut short by rain)

Soil CO₂ fluxes measured during May 1994 were similar at successive points along each transect, and baseline rates before tillage were similar for both transects. By 0.5 h after tillage, fluxes along the tilled transects increased 2 to 3-fold over the baseline rates, whereas fluxes along the undisturbed transect remained unchanged (Table 2). In both series, attempts to assess the persistence of the tillage-induced fluxes of CO₂ were hampered by rain. CO₂ fluxes from semi-arid cropland in this

Rates of soil CO₂ efflux

Soil CO₂ fluxes observed in this study were somewhat lower than those typically reported by others (e.g., Singh and Gupta, 1977; Norman et al., 1992), but were within the range for non-vegetated soils in more comprehensive studies at Lethbridge (Ellert, unpublished). Fluxes along the undisturbed transects, averaged across sequential measurements within a series, ranged from 0.22 to 0.34 μmol CO₂ m⁻² s⁻¹ for pre-plant wheat plots (series recorded in May 1994, 26 May 1996 and 10 June 1996) and from

Summary and conclusion

Our experimental approach had the sensitivity required to quantify the amounts of soil CO₂ susceptible to release by a single pass with a heavy-duty cultivator on loam soil at Lethbridge. Fluxes of soil CO₂ initially were equal, then immediately after tillage, increased at least 2-fold, but fluxes along tilled and undisturbed transects became similar between 10 and 24 h after cultivation. The tillage-induced flushes of CO₂ appeared to be independent of changes in soil temperature and moisture,

Acknowledgements

We greatly appreciate the skilled technical assistance of B.G. Johnson, O.O. Akinremi and F.J. Larney provided insightful comments on the manuscript. This work was funded by Agriculture and Agri-Food Canada's and Environment Canada's joint Greenhouse Gases program.

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Short-term influence of tillage on CO2 fluxes from a semi-arid soil on the Canadian Prairies

Abstract

Introduction

Section snippets

Site description

CO2 fluxes within 6 h of tillage (17 and 31 May 1994 series cut short by rain)

Rates of soil CO2 efflux

Summary and conclusion

Acknowledgements

Soil Till. Res.

Soil Till. Res.

Soil Till. Res.

Soil Till. Res.

Soil Biol. Biochem.

Sensitivity of total, light fraction and mineralizable organic matter to management practices in a Lethbridge soil

Can. J. Soil Sci.

Annual cycles of carbon dioxide in soil air

Soil Sci. Soc. Am. J.

Carbon sequestration in a Brown Chernozem as affected by tillage and rotation

Can. J. Soil Sci.

Soil aeration as affected by slope position and vegetative cover

Soil Sci.

The inhibition by CO2 of the growth and metabolism of micro-organisms

J. Appl. Bact.

Calculation of organic matter and nutrients stored in soils under contrasting management regimes

Can. J. Soil Sci.

Soil carbon dioxide fluxes from conventional and no-tillage small-grain cropping systems

Soil Sci. Soc. Am. J.

Short-term influence of tillage on CO₂ fluxes from a semi-arid soil on the Canadian Prairies

CO₂ fluxes within 6 h of tillage (17 and 31 May 1994 series cut short by rain)

Rates of soil CO₂ efflux

The inhibition by CO₂ of the growth and metabolism of micro-organisms