Problems with determining the particle size distribution of chalk soil and some of their implications

Abstract

Particle size distribution (psd) is one of the most important features of the soil because it affects many of its other properties, and it determines how soil should be managed. To understand the properties of chalk soil, psd analyses should be based on the original material (including carbonates), and not just the acid-resistant fraction. Laser-based methods rather than traditional sedimentation methods are being used increasingly to determine particle size to reduce the cost of analysis. We give an overview of both approaches and the problems associated with them for analyzing the psd of chalk soil. In particular, we show that it is not appropriate to use the widely adopted 8 µm boundary between the clay and silt size-fractions for samples determined by laser-based to estimate equivalent proportions of these size fractions to analyses based on sedimentation. 2We present data from field and national-scale surveys of soil derived from chalk in England. Results from both types of survey showed that laser methods tend to overestimate the clay-size fraction compared to sedimentation for the 8 µm clay/silt boundary, and we suggest reasons for this. For soil derived from chalk, either the sedimentation methods need to be modified or it would be more appropriate to use a 4 µm threshold as an interim solution for laser methods. Correlations between the proportions of sand-and clay-sized fractions, and other properties such as organic matter and volumetric water content, were the opposite of what one would expect for soil dominated by silicate

The importance of inorganic carbon in soil carbon databases and stock estimates: a case study from England

“…The overwhelming majority of the carbonate in the soil across our study region is primary (i.e. derived from bedrock); this has been demonstrated by the dominance of geogenic coccoliths in soil developed over the Cretaceous Chalk using scanning electron microscopy (Kerry et al. , 2009), but we do not have observations of the form of carbonate in soils over the Jurassic Limestone.…”

“…The overwhelming majority of the carbonate in the soil across our study region is primary (i.e. derived from bedrock); this has been demonstrated by the dominance of geogenic coccoliths in soil developed over the Cretaceous Chalk using scanning electron microscopy (Kerry et al, 2009), but we do not have Table 2) over two parent material types: (a) Cretaceous Chalk and associated Quaternary deposits (n = 45) and (b) Jurassic Limestone (n = 55). (Durr & Meybeck, 2005), so the soil IC stock associated with primary carbonate in many countries across Europe is likely to be larger than the global average.…”

Character, Rates, and Environmental Significance of Holocene Dust Accumulation in Archaeological Hilltop Ruins in the Southern Levant

“…This could be due to the platy and non-spherical shapes of phyllosilicates, which the laser interprets as spheres. The proposed correcting clay-silt borders range from 8 µm [140] over 6.2 µm [138] and 5 µm [11,54] to 4 µm [142]. Following previous studies of loess in the Negev [11], we decided to apply the 5 µm border.…”

Initial soil C and land‐use history determine soil C sequestration under perennial bioenergy crops

“…S1). This poor correlation appeared to be related to high soil inorganic C in five of the sites (2, 5, 7, 17 and 19), a factor known to affect laser assessment of clay content (Kerry et al ., ). Removal of these sites resulted in an improvement to an R 2 of 0.62 but did not improve the explanatory power of the percentage clay in regard to the percentage change in soil C stocks (Table S3).…”