Interactions between organisms and parent materials of a constructed Technosol shape its hydrostructural properties

Maha Deeb,Manuel Blouin,Anne Pando,Michel Grimaldi,Agnès Gigon,Thomas Z Lerch

doi:10.5194/soil-2-163-2016

Abstract

Abstract. There is no information on how organisms influence hydrostructural properties of constructed Technosols and how such influence will be affected by the parent-material composition factor. In a laboratory experiment, parent materials, which were excavated deep horizons of soils and green waste compost (GWC), were mixed at six levels of GWC (from 0 to 50 %). Each mixture was set up in the presence/absence of plants and/or earthworms, in a full factorial design (n = 96). After 21 weeks, hydrostructural properties of constructed Technosols were characterized by soil shrinkage curves. Organisms explained the variance of hydrostructural characteristics (19 %) a little better than parent-material composition (14 %). The interaction between the effects of organisms and parent-material composition explained the variance far better (39 %) than each single factor. To summarize, compost and plants played a positive role in increasing available water in macropores and micropores; plants were extending the positive effect of compost up to 40 and 50 % GWC. Earthworms affected the void ratio for mixtures from 0 to 30 % GWC and available water in micropores, but not in macropores. Earthworms also acted synergistically with plants by increasing their root biomass, resulting in positive effects on available water in macropores. Organisms and their interaction with parent materials positively affected the hydrostructural properties of constructed Technosols, with potential positive consequences on resistance to drought or compaction. Considering organisms when creating Technosols could be a promising approach to improve their fertility.

Highlights

Pedogenesis results from the dynamic interaction between climate, parent rock, and organisms
Two-way ANOVA showed that both green waste compost (GWC) percentage and the presence of earthworms had a positive effect on dry belowground, aboveground, and total biomasses (Table 2)
Earthworm presence had a positive effect on belowground biomass only at 50 % GWC, whereas aboveground biomass was affected only in the 0–30 % GWC range

Summary

Introduction

Pedogenesis results from the dynamic interaction between climate, parent rock, and organisms. The most important factor(s) has been debated for a long time (Wilkinson et al, 2009) and studied independently (Jenny, 1941), but their interactions remain little understood (Paton, 1978; Amundson et al, 2007). Understanding of the influence of bioturbation (physical displacement by organisms) is not straightforward on soil formation (Amundson et al, 2007; Wilkinson et al, 2009). Some authors consider biotic mixing agents as a secondary cause of soil formation (Carson and Kirkby, 1972), while others argue that bioturbation plays a major role in forming soil (Paton 1978; Wilkinson and Humphreys, 2005). When technogenic materials or artifacts are assembled deliberately to create soils, they are referred to as constructed Technosols (IUSS Working Group WRB, 2015). Many urban planners and green space enterprises are interested in constructed Technosols because these materials could be used as an alternative to topsoil material uptake from the countryside and the damage implied on the collecting site which

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Conclusion