Is manure an alternative to topsoil in road embankment restoration?

One of the main steps in road and railway embankment restoration is the spreading of previously removed topsoil, which provides an input of seeds, organic matter and microorganisms and encourages the establishment of a vegetation cover, essential to stabilise the embankment and blend it with the landscape. However, topsoil is a scarce resource, prompting the search for economic alternatives with similar results. The present study compares the results of spreading topsoil with an organic amendment (manure) for the soil's physico-chemical properties, erosion resistance and microbial activity, floristic richness and composition, and bare soil cover. For this purpose, experimental plots with three treatments (Control, Topsoil and Manure) were maintained on a recently built embankment in Central Spain for 20 months. Manure was found to be an effective alternative to topsoil for the improvement of soil fertility (organic matter content and total nitrogen). The two types of organic amendment produced similar reductions in bare soil cover and erosion rates. However, plots with topsoil showed greater soil respiration and species richness and a different floristic composition in comparison to those treated with manure, which was closer to control plots. These results suggest that manure can be used to replace topsoil to enhance embankment stability during the early stages of restoration. However, if the aim of the restoration process is to promote plant diversity, topsoil is recommended.

Spreading topsoil encourages ecological restoration on embankments: soil fertility, microbial activity and vegetation cover.

The construction of linear transport infrastructure has severe effects on ecosystem functions and properties, and the restoration of the associated roadslopes contributes to reduce its impact. This restoration is usually approached from the perspective of plant cover regeneration, ignoring plant-soil interactions and the consequences for plant growth. The addition of a 30 cm layer of topsoil is a common practice in roadslope restoration projects to increase vegetation recovery. However topsoil is a scarce resource. This study assesses the effects of topsoil spreading and its depth (10 to 30 cm) on two surrogates of microbial activity (ß-glucosidase and phosphatase enzymes activity and soil respiration), and on plant cover, plant species richness and floristic composition of embankment vegetation. The study also evaluates the differences in selected physic-chemical properties related to soil fertility between topsoil and the original embankment substrate. Topsoil was found to have higher values of organic matter (11%), nitrogen (44%), assimilable phosphorous (50%) and silt content (54%) than the original embankment substrate. The topsoil spreading treatment increased microbial activity, and its application increased ß-glucosidase activity (45%), phosphatase activity (57%) and soil respiration (60%). Depth seemed to affect soil respiration, ß-glucosidase and phosphatase activity. Topsoil application also enhanced the species richness of restored embankments in relation to controls. Nevertheless, the depth of the spread topsoil did not significantly affect the resulting plant cover, species richness or floristic composition, suggesting that both depths could have similar effects on short-term recovery of the vegetation cover. A significant implication of these results is that it permits the application of thinner topsoil layers, with major savings in this scarce resource during the subsequent slope restoration work, but the quality of topsoil relative to the original substrate should be previously assessed on a site by site basis.

Responses of arthropod fauna assemblages to goat grazing management in northern Spanish heathlands.

Changes in arthropod fauna assemblages after different goat grazing treatments (breeds and stocking rates) and responses to grazing cessation were studied in a heath-gorse shrubland located in northern Spain. Three treatments (low grazing pressure and high grazing pressure with Cashmere breed and high grazing pressure with local Celtiberic breed) with three replicates were randomly allocated to nine plots. Fauna data were collected three times per year during 3 grazing yr (2003, 2004, and 2005) and three times during 2007, i.e., 2 yr after grazing cessation. Arthropods were collected by 12 pitfall traps per plot, whereas vegetation cover and height were estimated by 100 random contacts per plot. Arthropod community composition was mostly affected by sampling year during the grazing period (between 2003 and 2005) but also between 2005 and 2007 (after cessation). Species composition differed between treatments, although the differences were not attributed to the stocking rates or to the goat breeds along those periods. Differences between treatments remained constant from 2003 to 2005 and between 2005 and 2007. Heather height explained most of the variance in arthropod species data during the last grazing year (2005), whereas heather cover was the most explanatory environmental variable 2 yr after grazing cessation (2007). Grazing effects still remained on both vegetation and fauna 2 yr after grazing cessation.