Dynamics of upward and downward N2O and CO2 fluxes in ploughed or no-tilled soils in relation to water-filled pore space, compaction and crop presence

Sharp peaks in nitrous oxide (N2O) fluxes under no-tillage in wet conditions appear to be related to near surface soil and crop cover conditions. Here we explored some of the factors influencing tillage effects on short-term variations in gas flux so that we could learn about the mechanisms involved. Field investigations revealed that a cumulative emission of 13 kg N2O–N ha−1 over a 12-week period was possible under no-tillage for spring barley. We investigated how reducing crop cover and changing the structural arrangement of the water-filled pore space (WFPS) by short-term laboratory compaction influenced N2O and carbon dioxide (CO2) fluxes in upward and downward directions in core samples from tilled and untilled soil. Increasing the downward flux of N2O within a soil profile by changing soil or moisture conditions may increase the likelihood of its further reduction to N2 or dissolution. We took undisturbed cores from 3 to 8 cm depth, equilibrated them to −1 or −6 kPa matric potential, incubated them and measured N2O and CO2 fluxes from the upper and lower surfaces in a purpose-designed apparatus before and after compaction in an uniaxial tester. We also measured WFPS, air permeability, bulk density and air-filled porosity before and after compaction. Spring barley was tested in 1999 and winter barley in 2000. Fluxes of N2O were from 1.5 to 35 times higher from no-tilled than ploughed even where the soil was of similar bulk density. Reduction of the crop cover increased CO2 flux and could reduce N2O flux. The effects of structural changes induced by laboratory compaction on the fluxes of N2O and CO2 were not influenced greatly by the tillage and crop cover treatments. Fluxes from the upper surfaces of cores (corresponding to 3 cm soil depth, upwards direction) could be up to ∼100 times greater (N2O) or ∼8 times (CO2) than from the lower surfaces (8 cm depth, downwards direction). These differences between surfaces were greatest when N2O fluxes were very high in no-tilled soil (4.2 mg N2O–N m−2 h−1) as occurred when WFPS exceeded 80% or became blocked with water, an effect that was increased by our compaction treatment. In general N2O fluxes increased with WFPS. The production and emission of N2O were strongly influenced by the soil physical environment, the magnitude of the water-filled pore space and continuity of the air-filled pore space in particular, produced in no-till versus plough cultivation.

[1]  B. Soane,et al.  THE CHARACTERIZATION OF SOME SCOTTISH ARABLE TOPSOILS BY AGRICULTURAL AND ENGINEERING METHODS , 1972 .

[2]  E. Hunter,et al.  Soil compactibility in relation to physical and organic properties at 156 sites in UK , 2000 .

[3]  J. Meisinger,et al.  Influence of Sample Size on Measurement of Soil Denitrification1 , 1987 .

[4]  R. Kachanoski,et al.  Field soil properties influencing the variability of denitrification gas fluxes , 1988 .

[5]  J. Doran,et al.  Effect of water-filled pore space on carbon dioxide and nitrous oxide production in tilled and nontilled soils [Maize; Illinois; Kentucky; Minnesota; Nebraska] , 1984 .

[6]  M. Busse,et al.  Compaction Alters Physical but Not Biological Indices of Soil Health , 2005 .

[7]  J. W. Dickson,et al.  Contributions of vehicle weight and ground pressure to soil compaction , 1990 .

[8]  J. K. Henshall,et al.  Soil structural quality, compaction and land management , 1997 .

[9]  Bruce C. Ball,et al.  Field N2O, CO2 and CH4 fluxes in relation to tillage, compaction and soil quality in Scotland , 1999 .

[10]  R. Q. Cannell,et al.  Factors influencing the variation of some properties of soils in relation to their suitability for direct drilling , 1984 .

[11]  B. Ball,et al.  Effects of uniaxial compaction on aeration and structure of ploughed or direct drilled soils , 1994 .

[12]  Keith A. Smith,et al.  Exchange of greenhouse gases between soil and atmosphere: interactions of soil physical factors and biological processes , 2003 .

[13]  J. K. Henshall,et al.  The effects of cultivation method and timing, previous sward and fertilizer level on subsequent crop yields and nitrate leaching following cultivation of long-term grazed grass and grass-clover swards , 2002, The Journal of Agricultural Science.

[14]  B. Ball,et al.  Crop performance and soil conditions on imperfectly drained loams after 20–25 years of conventional tillage or direct drilling , 1994 .

[15]  Nanthi Bolan,et al.  Transformation of nitrogen and nitrous oxide emission from grassland soils as affected by compaction , 2007 .

[16]  H. Di,et al.  Gross nitrogen mineralisation rates in pastural soils and their relationships with organic nitrogen fractions, microbial biomass and protease activity under glasshouse conditions , 2005, Biology and Fertility of Soils.

[17]  T. Clough,et al.  N2O and N2 gas fluxes, soil gas pressures, and ebullition events following irrigation of 15NO3–-labelled subsoils , 2003 .

[18]  K. Dobbie,et al.  The effects of temperature, water‐filled pore space and land use on N2O emissions from an imperfectly drained gleysol , 2001 .

[19]  Klaus Butterbach-Bahl,et al.  Carbon Sequestration in Arable Soils is Likely to Increase Nitrous Oxide Emissions, Offsetting Reductions in Climate Radiative Forcing , 2005 .

[20]  J. R. Burford,et al.  A LABORATORY METHOD TO MEASURE GAS DIFFUSION AND FLOW IN SOIL AND OTHER POROUS MATERIALS , 1981 .

[21]  Yoshitaka Uchida,et al.  Effects of aggregate size, soil compaction, and bovine urine on N2O emissions from a pasture soil , 2008 .

[22]  B. Ball,et al.  Long term monitoring of soil gas fluxes with closed chambers using automated and manual systems , 1999 .

[23]  G. Horgan,et al.  Spatial Variability of Nitrous Oxide Fluxes and Controlling Soil and Topographic Properties , 1997 .

[24]  R. Merckx,et al.  A system for studying the dynamics of gaseous emissions in response to changes in soil matric potential , 2004 .

[25]  Johan Six,et al.  The potential to mitigate global warming with no‐tillage management is only realized when practised in the long term , 2004 .

[26]  David S. Reay,et al.  Nitrous oxide emission from agricultural drainage waters , 2003 .

[27]  S. O. Petersen,et al.  Nitrous oxide evolution from structurally intact soil as influenced by tillage and soil water content , 2008 .

[28]  Kari Tanderup,et al.  Spatial and temporal effects of direct drilling on soil structure in the seedling environment , 2003 .

[29]  Jean Charles Munch,et al.  Emission of N2O, N2 and CO2 from soil fertilized with nitrate: effect of compaction, soil moisture and rewetting , 2006 .

[30]  H. Di,et al.  A field study of gross rates of N mineralization and nitrification and their relationships to microbial biomass and enzyme activities in soils treated with dairy effluent and ammonium fertilizer , 1999 .