Changes in soil organic carbon contents and nitrous oxide emissions after introduction of no-till in Pampean agroecosystems.
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.
Steinbach
Haydée S
HS
Facultad de Agronomía-Universidad de Buenos Aires. Av. San Martín 4453 (C1417DSE) Buenos Aires, Argentina. steinbac@agro.uba.ar
Alvarez
Roberto
R
D001118:Argentina; D002244:Carbon / Q000032:analysis*; D018556:Crops, Agricultural; D017753:Ecosystem; D009609:Nitrous Oxide / Q000032:analysis*; D009930:Organic Chemicals / Q000032:analysis*; D012987:Soil / Q000032:analysis*
D009930:Organic Chemicals; D012987:Soil; D002244:Carbon; D009609:Nitrous Oxide