Fabrizzi,K.P., Rice,C.W., Amado,T.J.C., Fiorin,J., Barbagelata,P. and Melchiori,R.(2009): Protection of soil organic C and N in temperate and tropical soils: effect of native and agroecosystems. Biogeochemistry, 92, 129-143.

『温暖および熱帯土壌における土壌有機炭素と窒素の保護：自然生態系と農業生態系の影響』

『Abstract
　Soil carbon sequestration is a viable short-term option to mitigate increased atmospheric CO2. 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.

Keywords: Aggregates; Tillage; Native grassland; No-tillage; Mollisol; Vertisol; Oxisol』

Abbreviations
Introduction
Materials and methods
　Site description
　Soil sampling
　Aggregate-size distribution
　Total C and N
　Total microbial biomass
　Statistical analysis
Results
　Total C and N
　Aggregate distribution
　Concentrations of C and N in aggregate fractions
　Microbial biomass
　Relationships among total C, soil aggregation and microbial biomass
Discussion
Acknowledgments
References

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