02974naa a2200517 a 450000100080000000500110000800800410001910000200006024501160008026000090019652016800020565000110188565000180189665000130191465000190192765000090194665000130195565000210196865000170198965000120200665000160201865000230203465000100205765000160206765000190208365000250210265000090212765000090213665000100214565000220215565000180217765000130219565300060220865300180221465300100223265300060224265300240224865300110227265300170228370000220230070000160232270000200233870000170235870000180237577300630239316281452005-05-09       2004    bl ---       0--  u    #d1 aSISTI, C. P. J.  aChange in carbon and nitrogen stocks in soil under 13 years of conventional or zero tillage in southern Brazil.  c2004  aThe objective of this study  was to determine in a long-term experiment 13 years the effect different crop rotations R1: wheat ( Triticum aestivum) - soybeam ( Glycine max), R2: wheat - soybean-vetch ( Vicia villosa)- maize (Zea mays), and R3: wheat-soybeam-oat (Avena sativa)- soybean-vetch-maize) under zero tillage (ZT) and conventional tillage (CT) on the stocks of soil organic matter (SOM) in a clayey Oxizol soil of Passo Fundo, Rio Grande do Sul. At the end of 13 years, soil samples were taken to a depth of 100 cm, and analused for bulk density, chemicla composition and 13C natural abudance. Under a continuous sequense of wheat (winter) and soybean ( summer) the stocks of soil organic C to 100 cm deph under ZT (168 Mg há-1 ) was not significantly different (LSD at P= 0.05 of 11 Mg há-1 ) to that under CT (168 Mg há-1 ) However, in the rotations with vetch planted as a winter gree-manure crop (R2 and R3), soil C stocks were approximately 17 Mg há-1  higher under ZT than under CT. Between 46 and 8% of this difference occurred at 30-85 cm deph. The 13C abundance data indicated that under ZT the decomposition of the original native  SOM was not affected by the different composition of crops in the different rotations, but under CT the rotations R2 nad R3, which included vetch and maize, stimulated the decay of the original native  SOM  compared to the continuous wheat/soybean sequence (R1). It appears that the contribution of N² fixation by the leguminous green manure (vetch) in the cropping system was the principal factor responsiblefor the observed C accumulation in the soil under ZT, and that most accumulated C was derived from crop roots.  acarbon  agreen manures  anitrogen  aorganic matter  asoil  asoybeans  aAdubação Verde  aAvena Sativa  aCarbono  aGlycine Max  aMatéria Orgânica  aMilho  aNitrogênio  aPlantio Direto  aRotação de Cultura  aSoja  aSolo  aTrigo  aTriticum Aestivum  aVicia Villosa  aZea Mays  aC  aDirect sowing  aMaize  aN  aRotational cropping  aWheats  aZero tillage1 aSANTOS, H. P. dos1 aKOHHANN, R.1 aALVES, B. J. R.1 aURQUIAGA, S.1 aBODDEY, R. M.  tSoil & Tillage Research, Amsterdamgv. 76, p. 39-58, 2004.