1. UCD School of Biology and Environmental Science
Presented by
Anurag Saha
Student No:
UCD School of Biology and Environmental Science

2. No-tillage (NT): A system for planting crops without ploughing, using herbicides to control weeds and resulting in reduced soil erosion and the preservation of soil nutrients.
Greenhouse Gases (GHGs): Atmospheric gases that contribute to the greenhouse effect by absorbing infrared radiation produced by solar warming of the Earth's surface. They include carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and water vapour.
Global Warming Potential (GWP): It is the relative measure of how much heat a greenhouse gas traps in the atmosphere.
Carbon sequestration: A natural or artificial process by which carbon dioxide is removed from the atmosphere and held in solid or liquid form.

3. OVERVIEW
Globally, agricultural sector has the potential to reduce GHGs by PgC equivalents per year (Cole et al., 1997).
No-tillage (NT) farming has been promoted to create a 'win-win' situation by reducing soil erosion and enhancing agricultural sustainability by mitigating Greenhouse gas (GHG) emissions (Paustian et al., 1997; Schlesinger, 1999).
NT management has been promoted as a practise capable of offsetting GHG emissions because of its ability to sequester carbon in soils.
The overall impact of NT adoption reduces the net global warming potential (GWP) determined by fluxes of the three major biogenic GHGs, i.e., CO2, N2O and CH4.
(contd….)

4. OVERVIEW
Available data of soil-derived GHG emission were compared between conventional tilled (CT) and NT systems for humid and dry temperate climates.
The newly converted NT systems showed a increasing effect to GWP with relation to CT practices in both the climatic conditions.
Only longer-term adoption (>10 years) significantly reduces GWP in humid climates.
By considering over a period of 20 years, the mean cumulative GWP is reduced even in dry areas, but with a degree of uncertainty.
Emissions of N2O drive much of the trend in net GWP.
Improved nitrogen management is essential to realize the full benefit from carbon storage in the soil for global warming mitigation.

6. To assess the potential global warming mitigation with the adoption of NT in temperate regions.
By compiling the available data reporting the differences in fluxes of soil-derived C, N2O and CH4 between CT and NT systems.
The analysis will provide a broader assessment of the role of NT for GHG mitigation purposes.

8. METHODS & MATERIALS Literature review
Studies which had direct comparisons between NT and CT in order to isolate the effect of tillage from other management change may accompany NT adoption.
Only included if there was constancy in edaphic and topographic characteristics.
Dataset used:
254 data points for soil Carbon.
44 data points for N20.
5 data points for CH4 fluxes.
Divided the dataset into humid and dry climate subsets based on Holdridge Life Zones classification (Holdridge et al., 1971) where;
PE : mean AP :: > 1 (dry climates)
PE : mean AP :: < 1 (humid climates).

9. Holdridge Life Zones classification
Figure 1: Location of agricultural experiment sites included in the analysis.

10. METHODS & MATERIALS Statistical Analyses
Differences in soil organic storage between NT and CT systems were analyzed in a linear mixed-effect model, with fixed effects for depth, climate (wet or dry) and years since the management change (Ogle et al., 2003).
Individual depth increments were not aggregate in the model.
To accommodate the data from different increment ranges, the effect of depth on soil organic carbon is used as a quadratic function.
Possibly allows the management impacts to be greatest at the surface and diminish with depth.
The soil organic carbon was measured on a particular depth increment;
(U = upper endpoint of increment in cm.) (L = lower endpoint of increment in cm.)
Assumption: the integrated average of the quadratic function over the increment.

11. (Statistical analyses…using S-PLUS 2000 software)
Two regressional equations were formed;
x1 = (L2 – U2) / (2 x [L – U])
x2 = (L3 – U3) / (3 x [L – U]) … (1).
Estimating the difference in soil organic storage for the specific year;
ΔSOC = Xt / t … (2).
(t is the year of interest and Xt is the cumulative value, by the linear mixed-effect model).
The uncertainty in an estimate for a single year was assessed using;
Var(ΔSOC) = 1 / t2 x (Var[Xt]) … (3).
(where, Var(Xt) is the estimated variance for the cumulative change in year t)
For obtaining a cumulative estimate at t years (i.e. 20 yrs.);
ΔN2O = X1 + X2 + ··· + Xi … (4).
(Xi is the annual difference in N2O flux between CT and NT systems, and t is the total number of years for the cumulative estimate)
Uncertainty was estimated as; Var(Y) = x’Vx … (5).
(where, x is the summed covariate vector for the regression coefficients of the linear mixed-effect model, and V is the estimated variance-covariance matrix for the coefficients.
To estimate the cumulative impact of management change; ΔCH4 = Xt … (6).
Corresponding uncertainty was estimated as; Var(ΔCH4) = t2Var(X) … (7).
Difference in CH4 fluxes had been evaluated in four studies.

12. (GLOBAL WARMING POTENTIAL CALCULATIONS)
The IPCC factors (IPCC, 2001) were used to calculate the GWP in CO2-equivalents ha-1 yr-1 over a 100-year time period.
To estimated the differences in SOC, N2O and CH4, the following equations were used;
ΔGWP(CO2) = ΔSOC x 44/12 x (-1) … (8).
ΔGWP(N2O) = ΔN2O x … (9).
ΔGWP(CH4) = ΔCH4 x … (10).
Further, the total GHG balance or net GWP is calculated as;
ΔGWP = ΔGWP(CO2) + ΔGWP(N2O) + ΔGWP(CH4) … (11).
By combining the uncertainties for the total GWP calculation, the individual variances were converted into CO2 equivalents and summed those values using the equation;
Var(ΔGWP ) = Var[(ΔGWP(CO2)] + Var[ΔGWP(N2O)] + Var[ΔGWP(CH4)] … (12).
The square root of the sum is the estimated standard deviation
This computation of uncertainty implicitly assumes that the three components of total GWP are uncorrelated. If there were non-negligible correlations, the estimated variance could increase or decrease depending on the signs and magnitudes of correlations.

13. RESULTS AND DISCUSSION

14. SE = standard error and GWP units are CO2 equivalents
(kg ha-1 yr-1). Soil-derived estimates are based on output of linear mixed-effect modelling of all currently available data.
Ancillary greenhouse gas (GHG) changes are due to changes in agricultural input (e.g., fuel); adopted from West and Marland (2002). Negative numbers indicate a reduction in global warming potential or a mitigation of global warming.
Source:
© 2004 Blackwell Publishing Ltd, Global Change Biology, 10, 155–160

15. CONCLUSION
Highly significant that the overall effect of N2O emissions on the net balance of GHG fluxes under NT fundamentally changes the GWPs over time.
The current uncertainty of these GHG gases estimates the net balance as quite large.
Current promotion of NT agriculture to reduce GHG emissions need certain additional consideration to benefit carbon sequestration.
Before encouraging any NT practice, it is advisable to seek for scientific assessment and understanding for both short and long term changes upon any land management.
It becomes quite crucial to further investigate the long-term as well as the immediate effects of various N-management strategies.
Such as precision farming, nitrification inhibitors, and type plus method of N fertilizer application, for purposes of long-term reduction of N2O-fluxes under NT conditions.
By increasing the utility of N fertilizer, the long-term N2O reduction would represent a very desirable and more definite ‘win-win’ situation.

16. Left: Share of arable land on which conventional tillage is applied.
Right: Share of arable land on which no-tillage is applied.
EU-27, IS, NO, CH, ME and HR, 2010, NUTS2

18. REFERENCES
Cole CV, Duxbury J, Freney J et al. (1997) Global estimates of potential mitigation of greenhouse gas emissions by agriculture. Nutrient Cycling in Agroecosystems, 49, 221–228.
Paustian K, Andren O, Janzen HH et al. (1997) Agricultural soils as a sink to mitigate CO2 emissions. Soil Use and Management, 13, 230–244.
Schlesinger WH (1999) Carbon sequestration in soils. Science, 284, 2095.
Holdridge LR, Grenke WC, Hatheway WH et al. (1971) Forest Environments in Tropical Life Zones. Pergamon Press, Oxford.
Ogle SM, Eve MD, Breidt FJ et al. (2003) Management impacts on soil organic carbon storage in US agroecosystems: literature review and synthesis. Global Change Biology, in press.

19. The original journal can be found at: http://onlinelibrary. wiley