Maximum Bulk Density of British Columbia Forest Soils from the Proctor Test: Relationships with Selected Physical and Chemical Properties

Abstract

The widespread use of heavy equipment during timber harvesting and site preparation can lead to reduced soil productivity and warrants development of new methods to assess compaction. We evaluated the effects of soil particle density, organic matter, particle size distribution, extractable oxides, and plastic and liquid limits on the maximum bulk density (MBD) of forest soils in British Columbia. Soil samples were collected from 33 sites throughout British Columbia, covering the major forest and soil types of the province. The standard Proctor test was used to determine MBD and related parameters, including the gravimetric water content (W MBD) and porosity (f MBD) at which MBD was achieved. The signifi cance levels of single soil properties in predicting MBD were in the order plastic and liquid limits, organic matter, oxalate-extractable oxides, and particle size distribution. For all samples, liquid limit and clay were most closely related to MBD (R 2 = 0.83). Addition of organic matter to the model increased the regression coeffi cients, and oxidizable organic matter caused a greater increase than did total C. Stratifi cation of the sample set into groups based on plasticity led to higher R 2 values in multiple regressions, and different soil properties were important for nonplastic soils than for those with high, moderate, and low plasticity. Prediction with multiple regression explained the most variation in MBD for nonplastic soils, while properties of highly plastic soils explained the least variation in MBD and moderately plastic soils were intermediate. Based on our fi ndings, we propose an approach for using MBD to help better interpret bulk density data in forest soil compaction studies.

Compaction of Coarse-Textured Soils: Balance Models across Mineral and Organic Compositions

“…We showed the importance of mineral cementing agents in predicting MBD of agricultural soils, as found by Zhao et al (2008) for forest soils in British Columbia, Canada. The Si, Al, Fe and Ca oxides increased CWC but reduced MBD.…”

“…The Si, Al, Fe and Ca oxides increased CWC but reduced MBD. Zhao et al (2008) found that Al and Fe oxides were positively related to CWC, but were negatively related to MBD. Concentrations of Si, Mn, Al, Fe, Ca and Mg oxides are positively related to CWC as such compounds are hydrophilic (Tschapek, 1984).…”

“…Bruand et al (2005) concluded that particlesize distribution and the mineralogy of silt and clay particles associated with sand can lead to variations in physical properties, e.g., water retention, resistance to penetration and permeability of sandy soil. Zhao et al (2008) reported that CWC was closely related to the liquid and plastic limits that integrate several soil properties such as particle-size distribution, organic matter content, and clay mineralogy. Hence, CWC could be predicted more accurately using liquid and plastic limits (Soane et al, 1972).…”

“…However, the variation in MBD has been attributed to changes in particle-size distribution (Nhantumbo and Cambule, 2006;Zhao et al, 2008), especially clay and silt contents (Bennie and Burger, 1988). The CWC was predicted from soil texture and organic matter content (Aragón et al, 2000).…”

Soil Compressibility under Irrigated Perennial and Annual Crops in a Semi-Arid Environment

“…The relationship between TOC and ρ max has been identified by other authors (Díaz-Zorita and Grosso, 2000;Blanco-Canqui et al, 2009;Viana et al, 2011). Others studies have shown that the degree of humification (Zhang et al, 1997) and the levels of oxidisable organic matter (Zhao et al, 2008) contribute more to reduction of ρ max than TOC does.…”