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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

^* Corresponding author (steinbac{at}agro.uba.ar)

Received for publication February 10, 2005. We reviewed published results to estimate no-till effects on SOC and denitrification in the Argentine Pampas and the potential of no-till to mitigate the global warming effect. On an equivalent mass basis, 42 paired data sets were used for SOC comparisons of no-till vs. plow till (moldboard plow or disk plow), 18 paired data for comparison of no-till vs. reduced till (chisel plow or harrow disk), and 20 paired data for comparison of plow till vs. reduced till. Twenty-six denitrification data sets were used for evaluation of tillage system and fertilization effects on N₂O emission. Changes in SOC under no-till were not correlated to time since initiation of experiments. Averaged over years a 2.76 Mg ha^–1 SOC increase (P = 0.01) was observed in no-till systems compared with tilled systems, but no differences were detected between plow and reduced till. The SOC under tillage explained most of the SOC variation under no-till (R² = 0.94, P = 0.01). The model had a positive intercept and predicted a relatively higher increase of SOC in areas of low organic matter level. The conversion of the whole pampean cropping area to no-till would increase SOC by 74 Tg C, about twice the annual C emissions from fossil fuel consumption of Argentina. Emissions of N₂O were greater under no-till with a mean increase of 1 kg N ha^–1 yr^–1 in denitrification rate for humid pampean scenarios. The increased emissions of N₂O might overcome the mitigation potential of no-till due to C sequestration in about 35 yr, and therefore no-till might produce global warming.

Abbreviations: NT, no-till • PT, plow till (moldboard plow or disk plow) • RT, reduced till (chisel plow or harrow disk) • SOC, soil organic carbon • SOC, differences in soil organic carbon between tillage systems

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