This study evaluated the effects of conservation agriculture and conventional tillage practices on aggregate stability and soil organic carbon distribution in different aggregate fractions. Specifically, it compared zero tillage with and without crop residue retention to conventional tillage with and without residue retention over multiple cropping cycles of maize and wheat. The study found that zero tillage systems with residue retention led to greater total soil organic carbon levels, especially in small and large macroaggregates, compared to conventional tillage systems. Maintaining crop residues on the soil surface under no-till was the most effective practice for maximizing carbon retention in the soil.

1. CONSERVATION AGRICULTURE, AGGREGATE STABILITY AND THE ORGANIC CARBON DISTRIBUTION IN SOIL AGGREGATES Mariela Fuentes, Luc Dendooven, Fernando De León, Jorge Etchevers, Claudia Hidalgo, Bram Govaerts

2. Carbon dynamics *Soil quality *Mitigation of climate change Conservation agriculture vs conventional

3. Aggregates

4. Evaluated aggregate size distribution, and carbon distribution in three aggregate fractions during a cropping cycle of a soil cropped with maize and wheat in Central Mexico.

5. EXPERIMENTAL STATION OF “EL BATÁN” CIMMYT Conventional tillage Zero tillage with without with without residues residues residues residues rotation maize-wheat,wheat-maize monoculture (maize and wheat) ZTM+r / -r ZTR+r / -r CTM+r / -r CTR+r /-r *The experiment was set up in 1991 *Subtropical highlands of central Mexico *Haplic Phaeozem 25% sand 37% silt and 38% clay

6. Samples undisturbed 0-5 and 5-10 cm soil layers micro-aggregates (< 0.25 mm) small macro-aggregates (0.25 to 1 mm) large macro-aggregates (1 to 8 mm) C autoanalyzer (TOC-5050A Total Organic Carbon, Shimadzu©)

7. MAIZE 0 to 5 cm 5 to 10 cm MWD 0.29 WHEAT MWD 0.57 MWD 0.7

8. MAIZE WHEAT 0 to 5 cm 5 to 10 cm

9. WHEAT MAIZE 0 to 5 cm layer 5 to 10 cm layer

10. Large macro-aggregates small macro-aggregates microaggregates Aggregates size distribution and their SOC contribution CONSERVATION AGRICULTURE CONVENTIONAL AGRICULTURE 0 to 5 cm layer Total SOC= 22 g kg-1 5 to 10 cm layer Total SOC= 15 g kg-1 0 to 5 cm layer Total SOC= 13 g kg-1 0 to 5 cm layer Total SOC= 13 g kg-1

11. CONCLUSION *The most attractive system to maximize C retention was zero tillage with residue (rotation or monoculture) *The retention of C depends mainly the small and large macro-aggregates

12. We know more about the movement of the celestial bodies than about the soil underfoot Da vinci Thank you very much