The influence of tillage and soil properties on soil organic matter fractions and dynamics in soils from New York and Brazil.

摘要

Soil organic matter (SOM) is a key component in productive sustainable systems, in addition to the relation to global climate change. Compartmental models have been developed to express the dynamics of soil organic carbon in different systems, emphasizing a diverse series of controls. The evaluation of the effects of tillage, soil aggregation and associated soil properties (mineralogy and texture) as controls on SOM dynamics was the focus of this project. The dynamics of SOM was examined in a tillage experiment in northern New York State and in Oxisols from Brazil under different land-uses. A physical fractionation procedure was employed to obtain particulate and mineral associated OM, and the 13C natural abundance technique was used to evaluate the distribution of crop derived carbon amongst soils and fractions. In the New York soil, total organic carbon (TOC) content significantly decreased only under the conventional tillage/silage harvest treatment relative to the grassland (back ground vegetation), but carbon in the particulate OM fraction was significantly lower in all treatments than in the grassland. Organic carbon in the particulate OM fraction ranged from 9.3--13.5% in the whole soil but only 2.9--7.8% of the TOC in 2--4 mm aggregates. Crop derived carbon (new carbon) was significantly higher in tilled relative to no-till treatments, probably as a result of the decrease in aggregate stability when soils were plowed. New carbon was approximately evenly distributed between particulate and mineral associated OM fractions and was higher in macro than microaggregates.; In Oxisols, differences among TOC concentrations in 2--4 mm aggregates were explained by a positive relationship with particle size distribution, and where texture was similar, by a land use effect. A decrease in TOC was found under soybean crop, but not under pasture relative to the original vegetation. The particulate OM fraction in 2--4 m aggregates ranged from as low as 1.2 to 16.3% of TOC. A negative relationship was obtained between carbon contents in the particulate OM and particle size distribution. Methodological issues are discussed, especially relative to the fractionation procedure and the presence of charcoal, derived from woody vegetation, that affects assessment of SOM dynamics in the Oxisols studied.