The contribution of rock fragments to the available water content of stony soils: Proposition of new pedotransfer functions

Abstract

The contribution of rock fragments to the soil available water content (SAWC) of stony soil has been quantified by measurements of bulk density and gravimetric water content at different water potentials on rock fragments of different lithologies: flints, cherts, chalks, gaizes and limestones. More than 1000 pebbles (2 cm b equivalent diameter of the rock fragment b 5 cm) have been sampled in stony soils developed from each of the five lithologies. We demonstrated that the water content at saturation of the studied pebbles was equal to the water content at −100 hPa and to the water content at field capacity. A linear relationship between the water content at −100 hPa and at −15,840 hPa enabled to derive a simple pedotransfer function to determine the available water content of the rock fragments. We also proposed a second simple pedotransfer function, which expresses the available water content from the dry bulk density of the rock fragments only. A simulation at the horizon scale for a loamy-clay stony horizon showed that the SAWC could be strongly misjudged when the rock fragments were not taken into account: for a stony horizon containing 30% of pebbles, the SAWC is underestimated by 5% for chert pebbles and by 33% for chalk pebbles.

Effect of Caliche Nodules on Soil Water Storage in the Northern Loess Plateau of China

“…Generally, large particles can be classified into two groups: the first is relatively soft chalk and sedimentary fragments called rock fragments, which differ from soil particles such as pebbles and flint stones; the second is caliche nodules, which are a product of soil genesis processes. Owing to the differences in size and physical and chemical properties, large particles can greatly affect some soil physical properties, such as bulk density and porosity, and affect soil–water processes such as evaporation, infiltration, runoff and sediment, and soil water movement . However, large particles are often removed from soil particles in traditional soil physical measurements and are often ignored in soil–water process studies.…”

“…However, an unbalance in soil water supply and vegetation water requirements is becoming evident, which affects vegetation restoration efforts as it makes vegetation construction unsustainable in the region . Caliche nodules have a relatively high capacity of water absorption compared to rock fragments . High water absorption by caliche nodules will inevitably change the soil water status and availability .…”

Effect of rock fragments content on water consumption, biomass and water-use efficiency of plants under different water conditions

“…Li et al, 2008;Zhou et al, 2009;Baetens et al, 2009;Ma et al, 2010;Novák et al, 2011;Tetegan et al, 2011). Water movement in, and the hydraulic properties of, soils are strongly dependent on the availability of water for plants.…”

“…Rock fragments in stony areas should therefore be considered in studies of water availability for plants and of water exchange among plants, rock fragments and soils. Tetegan et al (2011) proposed pedotransfer functions based on the linear relationship between the available water content (AWC) of rock fragments and the Napierian logarithm of bulk density and the relationship between water content at −100 and −15 840 hPa. The simulation showed that excluding 30% of the pebbles in a stony horizon underestimated the soil available water content (SAWC) by 5% for chert pebbles and by 33% for chalk pebbles.…”

“…Novák and Kňava (2012) demonstrated that the presence of stones can decrease soil water-holding capacity and hydraulic conductivity, which can decrease the availability of soil water for trees. (Tetegan et al, 2011) to calculate the SAWC at a regional scale (36 200 ha). They demonstrated that rock fragments could contribute to the AWC of stony soils.…”