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Changes in Soil Organic Carbon Contents and Nitrous Oxide Emissions after Introduction of No-Till in Pampean Agroecosystems

Facultad de Agronomía-Universidad de Buenos Aires. Av. San Martín 4453 (C1417DSE) Buenos Aires, Argentina

View larger version (16K): [in a new window]   Fig. 1. Map of the Pampean Region with four main provinces delimited and location of field experiments.

View larger version (15K): [in a new window]   Fig. 2. Differences in soil organic C between tillage systems (SOC) from experiments conducted in the Argentine Pampa Region related to experiment duration. (a) SOC calculated for fixed depth, (b) SOC calculated on an equivalent mass basis. SOC = NT – PT (solid circles) denotes SOC differences between no-till and plow till. SOC = NT – RT (open circles) denotes SOC differences between no-till and reduced till (chisel and disk till).

View larger version (20K): [in a new window]   Fig. 3. Relationship between changes in SOC (SOC = SOC no-till – SOC tilled treatments) estimated on equivalent mass basis and changes in SOC (SOC) C estimated for fixed depths, from experiments conducted in the Argentine Pampa Region. SOC NT – PT (solid circles) denotes SOC differences between no-till and plow till. SOC NT – RT (open circles) denotes SOC differences between no-till and reduced till (chisel and disk till).

View larger version (12K): [in a new window]   Fig. 4. Annualized soil organic C differences related to experiments duration from experiments conducted in the Argentine Pampa Region. (a) SOC calculated for fixed depth, (b) SOC calculated on an equivalent mass basis. SOC NT – PT (solid circles) denotes SOC differences between no-till and plow till. SOC NT – RT (open circles) denotes SOC differences between no-till and reduced till (chisel and disk till).

View larger version (17K): [in a new window]   Fig. 5. Relationships of soil organic C (SOC) between no-till and plow or reduced till, from experiments conducted in the Argentine Pampa Region, calculated for fixed depth (a) and on an equivalent mass basis (b). PT (solid circles) denotes plow till, and RT (open circles) denotes reduced till (chisel and disk till).

View larger version (18K): [in a new window]   Fig. 6. Relative change in soil organic C (SOC) of no-till to SOC in plow till from experiments conducted in the Argentine Pampa Region. Data were estimated using equations fitted in Fig. 5. NT, no-till; PT, plow till.

View larger version (21K): [in a new window]   Fig. 7. (a) Map of the Argentinean Pampean Region with areas delimited by different soil organic C contents in the 0- to 20-cm depth (Mg ha–1) calculated from soil survey performed before no-till introduction. (b) Potential relative change in soil organic C by adoption of no-till (%) calculated on an equivalent mass basis using equations from Fig. 5.

View larger version (14K): [in a new window]   Fig. 8. (a) Relationship between N denitrified between no-till and plow till and (b) relationship between N denitrified and N rate from experiments conducted in the Argentine Pampa Region.

View larger version (11K): [in a new window]   Fig. 9. Carbon mitigation potential under no-till in the Argentine Pampa Region. Estimations were performed assuming a C sequestration of 460 kg C ha–1 yr–1 under no-till between Years 4 to 9 from installation, a C saving of 31 kg C ha–1 yr–1 due to lower fuel consumption and an increase of 1 kg C soil kg–1 N fertilizer applied, with rates of 20 kg N ha–1 greater for corn and wheat under the wheat/soybean–corn–soybean rotation. An increase of 1 kg N–N2O emitted by denitrification under no-till was also assumed.