Reduced CO2 emissions using conservation agriculture

In terms of CO2 emissions, CA results in a reduction of C emissions and may also help sequester C in the soil. Minimal soil disturbance results in less exposure of the soil organic matter to oxidation and lower CO2 emissions to the atmosphere compared to tilled soils. As mentioned previously there are also significant savings in diesel use and thus lower CO2 emissions. This can be significant as shown from data collected in the rice-wheat systems of South Asia (Erenstein et al., 2008). The data from their 2003/04 survey of farmers adopting zero tillage in Haryana (India) and Punjab (Pakistan) indicated an average saving of 35 l of diesel for land preparation, or 98 kg C/ha. Farmers averaged one pass of the tractor with zero tillage for seeding versus eight passes for tilled soils. The soil physical properties left after rice cultivation are poor and it takes multiple passes of a tined cultivator to get what farmers feel is a suitable tilth for planting wheat. One litre of diesel contains 0.74 kg C and emits 2.67 kg CO2 (Environmental Protection Agency, 2009). More data on fossil fuel reduction through zero tillage can be found in Ortiz-Monasterio et al. (Chapter 9, this volume).

There are numerous reports that show that zero tillage, and especially zero tillage with crop residue retention, can result in increased soil C in the surface layers. In order to better understand the influence of different management practices, with special emphasis on tillage, crop rotation and residue management, on C sequestration, Govaerts et al. (2009a) did an extensive literature review. Some of the already existing reviews on the influence of agriculture and management on C sequestration made by West and Post (2002), Jarecki and Lal (2003), VandenBygaart et al. (2003) and Blanco-Canqui and Lal (2008) were used as a basis and completed through a further literature search. In seven of the 78 cases chosen, the soil C stock was lower in zero tillage compared to conventional tillage, in 40 cases it was higher and in 31 cases there was no significant difference. Another review of 67 long-term experiments that included 276 paired treatments indicated that a change from conventional tillage to no till can sequester 57 ± 14 g C/m2/year (West and Post, 2002). As results do not always point in the same direction, more research is needed, especially in the tropical areas where good quantitative information is lacking. Traditionally, farmers have removed these residues for other uses such as feeding animals, buried them through tillage or in high production areas have mostly burnt them in the field. The latter releases a large quantity of GHGs and pollutes the air. More details on CA and its effect on C sequestration can be found in Ortiz-Monasterio et al. (Chapter 9, this volume).

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