1. Prez Nieto J, Valds Velarde E, Reyes YurameM, and Rodrguez Lara JChapingo University. State of Mxico, Mxico.Corresponding author: jperezn14@hotmail.com

2. Conservation agriculture can mitigate global warmingbyCO2N2O Organic carbon Moderatingand nitrogengreenhouse sequestrationgas emissionCTS involve retaining the residues of previous crops on soil.Its effects on soil organic carbon and nitrogen sequestration had been knownin the world, however in Mxico, there is limited information about the long-term (10 years) effects. 3. Objective and hypothesis Objective: to evaluate the effect of three tillage systems on soil organic carbon (SOC) and soil total nitrogen (STN) sequestration and properties associated in MOLLISOL in the Central Valley of Mexico.Hypothesis: No tillage (NT) and Minimum tillage (MT) systems would increaseorganic carbon and nitrogen concentrations at the soil surface compared withthe effects of Conventional tillage (CT), influencing carbon/nitrogen ratio.Hypothesis: additionally, this would reflect in higher SOC and STN under NTand MT than CT, and improve others physical and chemical characteristics ofthe soil. 4. Material and MethodsA field experiment was conducted in a Mollisol (Soil Taxonomy) from 1999 to 2008 at Agricultural Experimental Station of Chapingo University. In Central Valley of Mexico. 19o 29 N, 98 o 53 W, 2240m altitude. 5. Characteristics of treatmentsTreatments Cover with Soil tillagePlanting Weedresiduescontrol(%)No Tillage> 30UndisturbedNo-tillChemical(NT) seederMinimum > 30 Chisel plowingNo-tillChemicalTillage (MT) seederConventional< 15 MouldboardNo-tillMechanicTillage (CT) plowing,seeder and disking andChemical field cultivator Rotation cropping system:P. vulgaris or Z. mays in spring and summer cycle.T. aestivum or A. sativa in autumn and winter cycle. 6. Treatments evaluated Minimum tillage(MT) No tillage (NT)Conventionaltillage (CT) Corn (Z. Mays) was planted in spring and summer cycle 2008 in three treatments evaluated.NT and MT include more than 30% of cover with residuesof previous crops. 7. Soil sampleTreatments were arranged in a Latin-square designs with three replications in a plot of 46x46m.Undisturbed soil core samples were collected from five random places in a central square of 20mx20m.Soil samples were collected with a hand probe (5.7cm inside diameter x 3.0cm high).Data were collected in September 2008.Soil samples were collected at 0-3cm, 15-18cm and 30-33cm of soil depth. 8. Variables evaluatedVariableMeasureMethodBulk densityMg m-3 Dividing mass soil sample by volume of probeOrganic carbon (C)%Dry combustion using a Perkin Elmerconcentration2400 Series IINitrogen total (N)%Dry combustion using a Perkin Elmerconcentration2400 Series IISoil organic carbon (SOC)Mg C ha-1 Multiplying organic C by bulk density and depth (11cm)Soil total nitrogen (STN)Mg N ha-1 Multiplying N by bulk density and depth (11cm)Carbon/Nitrogen (C/N)Ratio of organic C (%) and N (%)Volumetric water content(%)Multiplying gravimetric water by bulk density by 100Data were analyzed by GLM and Tukey procedures of SAS. Statistical significance was evaluated at P0.05. 9. Results and Discussion 1.6 NTMT CTBulk density (Mg m-3) 1.4aaba c 1.2 1.00-315-1830-33Soil depth (cm)Plow pan Soil bulk density was not significantly influenced (P0. 05) by soil tillage treatments at 0-3cm and 15-18cm soil depth.Greater bulk density in CT at 30- 33cm, probably due to plow pan But it was significantly greater in CTresulting from more tillage than NT and MT at 30-33cm soiloperations. depth. 10. Results and Discussion 40 a NTMT CTSOC (Mg C ha-1) 30 b a 20 ca b bRetained residues of the previous crops 10 increases SOC at the soil surface.0 Larger SOC at 22-33cm in CT is probably0-1111 2222-33associated with higher bulk density Soil layer (cm)observed, as well as the mix of profile soil byplow tillage.SOC was significantly influenced (P0. 05)by soil tillage treatments.Long-term linear estimated C sequestrationSOC was significantly greater in NT thanrates were 4 Mg C ha-1 year-1 greater in NTMT and CT at 0-11 cm layer. The oppositethan CT.occurred at 22-33cm.Corresponding long-term C sequestrationAt 11-22cm soil layer it was not influenced under MT compared with CT was 2 Mg C ha-1by treatments.year-1 greater. 11. Results and Discussion5 NTMT CT4 aSTN (Mg N ha-1)b3 ac a2abb10 0-11 11 22 22-33The difference between levels ofSoil layer (cm)STN fixed under NT and MT compared with CT rangedSimilarly to SOC, STN varied between 0.72 and 1.44 Mg N ha-1.significantly with treatments at thesurface soil layer and at 22-33cm. Linear estimated N sequestrationRetained residues of the previousby conservation tillage systemscrops on the soil increases Nover the 10 years was from 72 tocycling and soil N content.144 Kg N ha-1 year-1. 12. Results and Discussion 25a15Volumetric water content (%)NTMT CT 20 ab12 a aCarbon/nitrogen ratio a baa 159b bb610NTMT CT3500 0-315-1830-330-315-18 30-33 Soil depth (cm)Soil depth (cm) Other characteristics like volumetricThe C/N ratio of the soil also was water content also was influenced byinfluenced by soil tillage treatments at soil tillage treatments at the surfacethe surface soil layer after ten years.soil layer after ten years.It was significantly greater in NT thanIt was significantly greater in NT andMT and CT at 0-11 cm layer. At the other MT than CT at 0-11 and 15-18 cm soillayers it was significantly the same.depth. At 30-33cm it was significantly the same. 13. In summaryThank you for your attention