However, acquiring and employing such new technology can be complex and very expensive and access to it may be limited. Recent technological advances have allowed the development of many new non-destructive methods, such X-ray computed tomography (Helliwell et al., 2013), thermo-time domain reflectometry sensors (Liu et al., 2008) and automated 3-dimensional laser scanning (Rossi et al., 2008) to determine ρ b. While several techniques for determination of ρ b have been developed (Grossman and Reinsch, 2002), no single standard exists. Besides the disturbance of the soil structure caused by the particular method, other constraints in ρ b assessment are the size and representativity of the sample. The choice of assessment method depends on the purpose of the measurement, the required accuracy and precision, the need for repeated measurements at the same location, costs, operator expertise, and equipment/time availability (Cresswell and Hamilton, 2002). The determination methods commonly used for determining soil volume have their particular limitations and their suitability for specific conditions. While measuring the mass of a soil sample is simple and routine, measuring its volume generates a degree of uncertainty (Hartge and Ellies, 1999). Soil bulk density is actually a function rather than a single value where only soil mass remains unaltered, but the water status of the sample must be stated when soil volume is measured (Grossman and Reinsch, 2002). Both wetting-drying and freezing-thawing cycles after tillage may also cause the p to increase because of natural soil reconsolidation (Assouline, 2011 Hu et al., 2012). It can also change as a consequence of root growth, rainfall or normal traffic (Drewry, 2006). However, the measurement technique used may have dramatic implications for calculating carbon mass in soils (Throop et al., 2012).īulk density is not an intrinsic soil property but depends on external conditions, with changes associated with a variety of factors and with various natural and anthropogenic processes (Zeng et al., 2013). In addition to physical and biological roles, it is also used to convert soil organic carbon (SOC) and other nutrients from content (e.g. Linked to soil hydraulic properties, it is vital in predicting rainfall-runoff-infiltration-erosion relationships, heat and gas exchange, seedling emergence, root growth, and crop yield (Siegel-Issem et al., 2005 Assouline, 2011). As a key state variable, p provides valuable information relating to porosity, compaction, and penetration resistance of soil (Horn et al., 2003). Soil bulk density ( ρ b) describes the spatial arrangement of the solid particles that compose soil matrix, providing an indication of basic soil quality index (Chan, 2005). However, soil quality cannot be directly determined, but can be inferred by measuring soil physical, chemical and biological properties. The variability in soil quality influences mainly biogeochemical cycling, biodiversity, and agricultural productivity. Key words: Alluvial soils, organic carbon, pedotransfer function, texture. This indicates that it is necessary to define a set of locally calibrated PTFs that address the complexity of the soil resource throughout Chile. Using basic information (texture and organic matter/C content) from the existing PTFs for both sites, a better fit for coarse-textured than fine-textured soils was obtained. In general, the clod technique tended to give higher values than the other methods. On the coarse-textured soil, there were nonsignificant differences between the excavation and clod methods, but medium-sized cylinders differed from other cylinder sizes. With the exception of small cylinders in fine-textured soil, there were nonsignificant differences between the methods and sample sizes assessed. Bulk density values obtained by direct methods (clod, cylinder, and excavation) with three sample sizes (small, medium, and large) were compared with those obtained by 10 published pedotransfer functions (PTFs) for two alluvial soils (a massive fine-textured Fluventic Haploxeroll and an aggregated, coarse-textured Fluventic Haploxerept) of central Chile. *Corresponding author ( significance of soil bulk density ( ρ) as a key indicator of soil quality was examined in this study. Manuel Casanova 1*, Elizabeth Tapia 1, Oscar Seguel 1, and Osvaldo Salazar 1ġUniversidad de Chile, Facultad de Ciencias Agronómicas, Casilla 1004, Santiago, Chile. Direct measurement and prediction of bulk density on alluvial soils of central Chile
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