See more from this Session: Conservation Practices to Mitigate the Effects of Climate Change: II
Wednesday, November 3, 2010
Long Beach Convention Center, Exhibit Hall BC, Lower Level
Agricultural soils could be sources or sinks of atmospheric C, according to soil management. Effects of tillage, crop residue, and macroaggregate disruption on soil C-CO2 efflux were evaluated on a subtropical Hapludox in Southern Brazil. Long-term (25 years) conventional tillage (CT) and no-till (NT) plots under intensive crop rotation were selected for this study. SOC stocks at the 0-0.30 m soil layer were 66.2 and 73.2 Mg C ha-1 for CT and NT, respectively. The treatments were: (T1) bare soil; (T2) soil + crop residues; (T3) disrupted bare soil (1 m2 sub-plot (0-0.15 m depth) disrupted with a shovel to crush all visible (~> 2 mm) soil aggregates). Crop residues (black-oat) levels were similar on CT and NT plots. Soil C-CO2 efflux was assessed using a LI-COR LI-8100 analyzer and a 20 cm survey chamber with six replications at the 9, 13, and 17 h, during 15 days (Dec/04-Dec/18/2009). Tillage operations were performed at the 1st (disk plow) and 5th (disk tandem) evaluation days. Soybean was seeded on the 11th day. C-CO2 efflux was highly affected by environmental conditions (rainfall, temperature). Average C-CO2 efflux from CT and NT soils (T1) were 21.5 and 19.0 kg C ha-1 day-1, respectively, 13.1% higher on CT even with 9.5% lower SOC stocks, showing that NT was more C conservative than CT. Aggregate disruption (T3) increased by 0.4 and 3.2% the average C-CO2 efflux under CT and NT, respectively, reflecting the larger POC stocks and intra-macroaggregate C stabilization under NT. Presence of crop residues (T2) increased 42.6 and 49.6% the C-CO2 efflux under CT and NT, respectively. Crop residues decomposition had larger impact on soil C-CO2 efflux than CT on this subtropical clayey Oxisol, contrasting to Reicosky and Lindstrom (1993) which reported high C-CO2 efflux after tillage on a temperate clay loam Mollisol.