Hydraulic properties of layered soils influence survival of Rhodes grass (Chloris gayana Kunth.) during water stress

Abstract

Survival of vegetation on soil-capped mining wastes is often impaired during dry seasons due to the limited amount of water stored in the shallow soil capping. Growth and survival of Rhodes grass (Chloris gayana) during soil drying on various layered capping sequences constructed of combinations of topsoil, subsoil, seawater-neutralised residue sand and low grade bauxite was determined in a glasshouse. The aim was to describe the survival of Rhodes grass in terms of plant and soil water relationships. The soil water characteristic curve and soil texture analysis was a good predictor of plant survival. The combination of soil with a high water holding capacity and low soil water diffusivity (e.g. subsoil with high clay contents) with soil having a high water holding capacity and high diffusivity (e.g. residue sand) gave best survival during drying down (up to 88 days without water), whereas topsoil and low grade bauxite were unsuitable (plants died within 18-39 days). Clayey soil improved plant survival by triggering a water stress response during peak evaporative water demand once residue sand dried down and its diffusivity fell below a critical range. Thus, for revegetation in seasonally dry climates, soil capping should combine one soil with low diffusivity and one or more soils with high total water holding capacity and high diffusivity.

Field-scale spatial variability of saturated hydraulic conductivity on a recently constructed artificial ecosystem

“…As observed in earlier studies (e.g. Wehr et al, 2005), soil moisture characteristic curves showed that residue sand had low water retention capacity. The van Genuchten pore size distribution index (n) was 3.58, while α, which is inversely related to the air-entry value was 0.15 kPa − 1 .…”

“…Botros et al, 2009;Gόmez et al, 2005;Sobieraj et al, 2002), there has been no systematic field evaluation of K s and its spatial variability for artificially constructed ecosystems such as engineered covers. The few studies conducted on mine waste disposal facilities or artificial catchments are based on indirect methods involving analysis of qualitative data on soil structure (Breshears et al, 2005;Buczko et al, 2001), while results of spatial analysis are often not reported probably due to small sample sizes that restrict such analysis (Gerwin et al, 2009;Holländer et al, 2009;Mazur et al, 2011;Wehr et al, 2005). Notable exceptions are two studies conducted in Germany, where geostatistical analysis of hydraulic parameters derived from pedotransfer functions developed for natural soils showed that particle segregation during transportation and dumping, and amelioration practices contributed to spatial variability on lignite mine spoils (Buczko et al, 2001;Buczko and Gerke, 2005).…”

Revegetation strategies for seawater neutralized bauxite residue at Rio Tinto Alcan using various amendments

“…The conventional remediation technique was capping in which a cap of soil from 20-200 cm deep was placed over the RDA (Wehr et al, 2005. A shallow cap can support grasses and herbs whilst deeper caps may support trees and shrubs (Mendez and Maier, 2008).…”

“…0.002 cm min -1 ) (Bell and Meecham, 1978). Residue sand (which is much coarser textured) has a lower water holding capacity than mud but a higher hydraulic conductivity (Wehr et al, 2005.Because of the low macroporosity and hydraulic conductivity of mud, water tends to pond on the surface and the upper layers can become saturated during wet periods of the year. Such waterlogging 17 can limit plant establishment (Pinnock and Gordon, 1992; Zhang et al, 2001; Newson et al, 2006).…”

“…It is a contradiction that on the one hand workers have described residue mud as being an unsuitable environment for root growth because of waterlogging in a structureless, pastey matrix of wet mud or alternatively, after drying, as being impenetrable to roots due to the formation of a massive, dense solid structure (e.g. Wehr et al, 2005). Nonetheless, there are several examples of successful revegetation Santini and Fey, 2013; Aluminium for Future Generations, 2016).…”