Distribuição Do Carbono Orgânico Nas Frações Do Solo Em Diferentes Ecossistemas Na Amazônia Central

Organic matter plays an important role in many soil properties, and for that reason it is necessary to identify management systems which maintain or increase its concentrations. The aim of the present study was to determine the quality and quantity of organic C in different compartments of the soil fraction in different Amazonian ecosystems. The soil organic matter (FSOM) was fractionated and soil C stocks were estimated in primary forest (PF), pasture (P), secondary succession (SS) and an agroforestry system (AFS). Samples were collected at the depths 0-5, 5-10, 10-20, 20-40, 40-60, 60-80, 80-100, 100-160, and 160-200 cm. Densimetric and particle size analysis methods were used for FSOM, obtaining the following fractions: FLF (free light fraction), IALF (intra-aggregate light fraction), F-sand (sand fraction), F-clay (clay fraction) and F-silt (silt fraction). The 0-5 cm layer contains 60% of soil C, which is associated with the FLF. The F-clay was responsible for 70% of C retained in the 0-200 cm depth. There was a 12.7 g kg-1 C gain in the FLF from PF to SS, and a 4.4 g kg-1 C gain from PF to AFS, showing that SS and AFS areas recover soil organic C, constituting feasible C-recovery alternatives for degraded and intensively farmed soils in Amazonia. The greatest total stocks of carbon in soil fractions were, in decreasing order: (101.3 Mg ha-1 of C - AFS) > (98.4 Mg ha-1 of C - FP) > (92.9 Mg ha-1 of C - SS) > (64.0 Mg ha-1 of C - P). The forms of land use in the Amazon influence C distribution in soil fractions, resulting in short- or long-term changes. © 2015, Revista Brasileira de Ciencia do Solo. All rights reserved

Spatial distribution of soil hydraulic parameters estimated by pedotransfer functions for the Jialing River Catchment, Southwestern China

Soil hydraulic parameters θ s, α, n, K s, L and θ r of the van Genuchten-Mualem model were estimated using three pedotransfer functions (PTFs) based on soil properties for surface soils of the largest main tributary catchment (the Jialing River) of the upper Yangtze River in China. The soil database was from the second national soil survey of China with a spatial 30 X 30 arc-second resolution. According to the statistical analysis of the differences between the continuous-PTFs-estimated values of soil hydraulic parameters for the study catchment and the reference values for a specific texture class provided in the development database of a specific PTF, best estimations were obtained using the Wösten PTF. The Rawls & Brakenssiek PTF was good estimation for parameter θ r that was assumed as zero by Wösten PTF. The established higher θ r (0.08%) and lower K s (20 cm/d) and θ s (0.43%) in the mid-downstream area relative to the other areas of the catchment could lead to larger amounts of surface runoff and consequently provide higher energy to erode soil. Thus, these factors provide a supporting explanation for previously reported severe soil erosion occurring in this area. Spatial heterogeneity analysis for estimated hydraulic parameters in terms of semivariogram showed that the spatial correlation distance was in the range of 50-80 km and that the spatial variability (sill) was not large except for parameters K s and L. The semi-variance with the exponential model at the zero distance (nugget) was 30%-50% of the sill. This study provided a practical PTF approach for estimating soil hydraulic properties from soil survey data at a large watershed scale. The estimation results could provide better insight into the mechanism of surface runoff and soil erosion, which is important to better understand and manage erosion in the catchment