Protection of soil organic C and N in temperate and tropical soils: effect of native and agroecosystems

Abstract

Soil carbon sequestration is a viable shortterm option to mitigate increased atmospheric CO 2 . In agriculture, strategies to increase the soil carbon (C) sink include no-tillage, cover crops, and improved crop rotation. The objective of this study was to determine the influence of tillage systems on SOC and total N, soil aggregation and aggregate associated C and N in three soil types: Oxisol (Brazil), Vertisol (Argentina), and Mollisol (USA). Long-term tillage experiments included tilled (T) and no-till (NT) systems. A native grassland was included for comparison in each site. Soil samples were taken at 0-5, 0-15, and 15-30 cm depths.Water-stable aggregates (WSA) were separated using a wet-sieving method. Total C and total N were determined by dry combustion. A shift from native grassland to an agroecosystem decreased microbial biomass, but this decrease was less pronounced under NT. Cultivation reduced the mass of macroaggregates and the concentration associated C and N; however among agroecosystems, NT, regardless soil type, tended to be more similar to the native grassland sites. Agroecosystems reduced TOC and total N stocks, regardless of soil type, compared to the native grassland. This effect followed: Mollisol [ Oxisol [ Vertisol, and was more pronounced at the 0-5 cm soil depth than at deeper depths. This loss of C and N was associated with the decrease in the mass of macroaggregates and lower C and N concentrations of the aggregates. Macroaggregation was related to TOC and microbial biomass in the Mollisol, suggesting that the biological process of aggregate formation is the principal mechanism of C protection in these soils. The relationship between TOC and large macroaggregates showed lower values for the Oxisol and Vertisol, indicating that in these soils TOC has a complementary role in macroaggregation.

Carbono em agregados do solo sob vegetação nativa, pastagem e sistemas agrícolas no bioma Cerrado

“…Muitos desses estudos mostram que a adoção do sistema plantio direto (SPD) conduz a maiores quantidades de MOS se comparado ao sistema plantio convencional (SPC) (Six & Jastrow, 2002;Ogle et al, 2003;Salton et al, 2008;Fabrizzi et al, 2009;Anders et al, 2010), concomitantemente com a formação de macroagregados (Pinheiro et al, 2004;Six et al, 2006). O aumento do estoque de C sob SPD é frequentemente atribuído ao maior conteúdo de material orgânico particulado adicionado aos primeiros centímetros do perfil do solo e ao menor distúrbio deste, comparado ao SPC, os quais são importantes fatores que intervêm na estabilização dos macroagregados (Six et al, 2000;Fabrizzi et al, 2003;Madari et al, 2005).…”

“…O aumento do estoque de C sob SPD é frequentemente atribuído ao maior conteúdo de material orgânico particulado adicionado aos primeiros centímetros do perfil do solo e ao menor distúrbio deste, comparado ao SPC, os quais são importantes fatores que intervêm na estabilização dos macroagregados (Six et al, 2000;Fabrizzi et al, 2003;Madari et al, 2005). R. Bras.…”

“…Nesse caso, agentes biológicos de agregação do solo possuem papel secundário nesse processo. Apesar do manejo realizado em situações climáticas semelhantes, os solos 2:1 apresentam maior perda de C, denotando ser mais vulneráveis às mudanças de uso e manejo do solo (Fabrizzi et al, 2009). …”

“…Assim, mais pesquisas são necessárias para elucidar os mecanismos e a sensibilidade devido às mudanças ambientais de manejo na agregação do solo associada à MOS (Fabrizzi et al, 2009;Fernández et al, 2010).…”

Mechanisms of organic matter stabilization and destabilization in soils and sediments: conference introduction

“…Charles Rice (see : Fabrizzi et al 2008 this volume) discussed further refinement of our understanding of the effects of tillage on C and N cycling, whilst Roland Bol addressed the implications of widespread amendment of soils with manure.…”