Potential of carbon accumulation in no-till soils with intensive use and cover crops in southern Brazil.

The area under no-till (NT) in Brazil reached 22 million ha in 2004-2005, of which approximately 45% was located in the southern states. From the 1970s to the mid-1980s, this region was a source of carbon dioxide to the atmosphere due to decrease of soil carbon (C) stocks and high consumption of fuel by intensive tillage. Since then, NT has partially restored the soil C lost and reduced the consumption of fossil fuels. To assess the potential of C accumulation in NT soils, four long-term experiments (7-19 yr) in subtropical soils (Paleudult, Paleudalf, and Hapludox) varying in soil texture (87-760 g kg(-1) of clay) in agroecologic southern Brazil zones (central region, northwest basaltic plateau in Rio Grande Sul, and west basaltic plateau in Santa Catarina) and with different cropping systems (soybean and maize) were investigated. The lability of soil organic matter (SOM) was calculated as the ratio of total organic carbon (TOC) to particulate organic carbon (POC), and the role of physical protection on stability of SOM was evaluated. In general, TOC and POC stocks in native grass correlated closely with clay content. Conversely, there was no clear effect of soil texture on C accumulation rates in NT soils, which ranged from 0.12 to 0.59 Mg ha(-1) yr(-1). The C accumulation was higher in NT than in conventional-till (CT) soils. The legume cover crops pigeon pea [Cajanus cajan (L.) Millsp] and velvet beans (Stizolobium cinereum Piper & Tracy) in NT maize cropping systems had the highest C accumulation rates (0.38-0.59 Mg ha(-1) yr(-1)). The intensive cropping systems also were effective in increasing the C accumulation rates in NT soils (0.25-0.34 Mg ha(-1) yr(-1)) when compared to the double-crop system used by farmers. These results stress the role of N fixation in improving the tropical and subtropical cropping systems. The physical protection of SOM within soil aggregates was an important mechanism of C accumulation in the sandy clay loam Paleudult under NT. The cropping system and NT effects on C stocks were attributed to an increase in the lability of SOM, as evidenced by the higher POC to TOC ratio, which is very important to C and energy flux through the soil.

[1]  G. Blair,et al.  Soil Carbon Fractions Based on their Degree of Oxidation, and the Development of a Carbon Management Index for Agricultural Systems , 1995 .

[2]  Rattan Lal,et al.  Managing U.S. cropland to sequester carbon in soil , 1999 .

[3]  C. Bayer,et al.  Organic matter storage in a sandy clay loam Acrisol affected by tillage and cropping systems in southern Brazil. , 2000 .

[4]  A. Franzluebbers,et al.  Particulate Organic Carbon Content and Potential Mineralization as Affected by Tillage and Texture , 1997 .

[5]  C. Bayer,et al.  Changes in Soil Organic Matter Fractions under Subtropical No‐Till Cropping Systems , 2001 .

[6]  E. T. Elliott,et al.  Particulate soil organic-matter changes across a grassland cultivation sequence , 1992 .

[7]  J. Baldock,et al.  Role of the soil matrix and minerals in protecting natural organic materials against biological attack , 2000 .

[8]  I. Kögel‐Knabner,et al.  Carbon and nitrogen stocks in physical fractions of a subtropical Acrisol as influenced by long-term no-till cropping systems and N fertilisation , 2005, Plant and Soil.

[9]  A. Walkley,et al.  A CRITICAL EXAMINATION OF A RAPID METHOD FOR DETERMINING ORGANIC CARBON IN SOILS—EFFECT OF VARIATIONS IN DIGESTION CONDITIONS AND OF INORGANIC SOIL CONSTITUENTS , 1947 .

[10]  J. M. Bremner,et al.  A rapid and precise method for routine determination of organic carbon in soil , 1988 .

[11]  S. Urquiaga,et al.  Change in carbon and nitrogen stocks in soil under 13 years of conventional or zero tillage in southern Brazil , 2003 .

[12]  A. Whitmore,et al.  A model of the physical protection of organic matter in soils , 1997 .

[13]  Flávio Luiz Foletto Eltz,et al.  Potencial de culturas de cobertura em acumular carbono e nitrogênio no solo no plantio direto e a melhoria da qualidade ambiental , 2001 .

[14]  Johan Six,et al.  Aggregation and soil organic matter accumulation in cultivated and native grassland soils , 1998 .

[15]  C. Bayer,et al.  C and N stocks and the role of molecular recalcitrance and organomineral interaction in stabilizing soil organic matter in a subtropical Acrisol managed under no-tillage , 2006 .

[16]  M. R. Carter,et al.  Soil Structural Form and Stability, and Organic Matter under Cool‐Season Perennial Grasses , 1994 .

[17]  T. Shepherd,et al.  Effects of clay minerals and land use on organic matter pools , 1997 .

[18]  Johan Six,et al.  Soil macroaggregate turnover and microaggregate formation: a mechanism for C sequestration under no-tillage agriculture , 2000 .

[19]  Claire Chenu,et al.  Relationship of soil organic matter dynamics to physical protection and tillage , 2000 .

[20]  Rattan Lal,et al.  Organic matter dynamics and carbon sequestration rates for a tillage chronosequence in a Brazilian Oxisol , 2001 .

[21]  C. Feller,et al.  Physical control of soil organic matter dynamics in the tropics , 1997 .

[22]  Johan Six,et al.  Aggregate and Soil Organic Matter Dynamics under Conventional and No-Tillage Systems , 1999 .

[23]  J. Mielniczuk,et al.  Effect of cropping systems on soil chemical characteristics, with emphasis on soil acidification* , 1997, Plant and Soil.

[24]  P. Machado,et al.  Soil organic carbon and fractions of a Rhodic Ferralsol under the influence of tillage and crop rotation systems in southern Brazil , 2002 .

[25]  I. Kögel‐Knabner,et al.  Soil C and N stocks as affected by cropping systems and nitrogen fertilisation in a southern Brazil Acrisol managed under no-tillage for 17 years , 2005 .

[26]  C. Bayer,et al.  Stocks and humification degree of organic matter fractions as affected by no-tillage on a subtropical soil , 2004, Plant and Soil.

[27]  Ladislau Martin-Neto,et al.  Carbon sequestration in two Brazilian Cerrado soils under no-till , 2006 .

[28]  J. Skjemstad,et al.  Study of free and occluded particulate organic matter in soils by solid state 13C Cp/MAS NMR spectroscopy and scanning electron microscopy , 1994 .

[29]  C. Bayer,et al.  Effect of no-till cropping systems on soil organic matter in a sandy clay loam Acrisol from Southern Brazil monitored by electron spin resonance and nuclear magnetic resonance , 2000 .

[30]  J. Mielniczuk,et al.  Adição de carbono e nitrogênio e sua relação com os estoques no solo e com o rendimento do milho em sistemas de manejo , 2004 .