Modelling long‐term carbon dynamics in soils reconstituted with large quantities of organic matter

Abstract

In urban conditions, the widescale availability of organic matter to be recycled and the necessity for soil reconstitution (Technosol) has led to the input of very large quantities of organic matter (up to 50% v/v). The long‐term degradation of these large quantities of organic matter in the soil is not well known. We monitored, over a 60‐month period, the total carbon (C) content and the particulate and biochemical fractions of reconstituted soils placed in 600‐litre boxes under natural conditions. The top layer was a sandy loam amended with 20 or 40% of sphagnum peat or organic compost (sewage sludge, wood chip compost or green waste compost) lying on a layer of sandy loam. We measured C mineralization over time under controlled conditions and built a long‐term model to simulate carbon dynamics where exogenous organic carbon (EOC) was divided into two biodegradable compartments. The model yielded the proportions of EOC that either resisted degradation or contributed to soil organic C storage by mineralization and/or humification. Organic matter degradation was linked to its maturity and to its contents in certain particulate and biochemical fractions but was independent of how much of a given organic matter was introduced. We found a good correlation between the degradable organic compartment and the lignin and cutin‐like, hemicellulose and cellulose‐like fractions larger than 1 mm. The model showed that a large part of initial EOC was still present in the soil after 5 years in a potentially biodegradable but resistant compartment. The degradation of that compartment by mineralization or humification is therefore expected to take longer.

Prediction of long‐term sustainability of constructed urban soil: impact of high amounts of organic matter on soil physical properties and water transfer

“…The organic carbon ( OrgC ) content of the compost treatments was modelled using the simulation proposed by Vidal‐Beaudet et al . () for the same experimental set‐up.…”

“…Organic carbon content (OrgC): this was determined (three replicates for each sample) by dry combustion using an elemental analyzer (Thermoquest FlashEA1112 â , Thermo Fisher Scientific, Waltham, MA, USA). The organic carbon (OrgC) content of the compost treatments was modelled using the simulation proposed by Vidal-Beaudet et al (2012b) for the same experimental set-up.…”

Are urban soils similar to natural soils of river valleys?

“…In the urban context, soil age, based on well-documented historical periods, was defined according to the date of soil settlement but the "real" date of birth was difficult to estimate because most of soils were originally formed by geomorphic processes (Gobat et al 2013). Several authors also reported an acceleration of soil pedogenetic processes due to human activities in urban soils (Strehler 1997;Baumgartl 1998;Vidal-Beaudet et al 2012). This trend can be first explained by the nature of the deposit.…”

“…Second, most recent human-made soils (1970JR, 1995HR, 2010PR and 1995HR) were made with different organic amendments such as com-post. The effects of the input of "anthropic" materials (organic or mineral) on soil processes are little known (Vidal-Beaudet et al 2012) although Strehler (1997) showed a rapid organic matter turnover in urban soils compared to natural soils.…”

“…Moreover, if organic matter can constitute an interesting indicator of soil evolution in river valley ecosystems (Pautou 1984;Bureau 1995;Fierz et al 1995), it remains difficult to apply it in the urban context. In urban ecosystems, organic matter quantity and their quality vary a lot between soils according to soil and land management modifying soil pro-cesses (Fierz et al 1995;Vidal-Beaudet et al 2012). First, the exportation of the litter can affect soil organic matter integra-tion through the soil fauna activity.…”