Topsoil can be a scarce resource, especially in big infrastructure projects where contractors are wanting to restore worked-over areas to grow vegetation or grass.
Researchers in Spain have come up with what they say is a viable alternative: Horse manure.
Begoña Peco and her colleagues found in a study that horse manure performed well when compared to topsoil.
The study team, writing in the open-access peer-reviewed journal PLOS ONE, said one of the main steps in road and railway embankment restoration was the spreading of previously removed topsoil. It provided an input of seeds, organic matter and microorganisms and encouraged the establishment of vegetation, which was essential in stabilising land.
However, topsoil was a scarce and valuable resource, prompting the search for economic alternatives that delivered similar results.
“There is often a shortage of topsoil in civil engineering works. For this reason, when not enough fertile soil is available to restore the entire disturbed area, poor quality soil from deeper layers is employed, compromising the success of the restoration process.”
The researchers set out to compare the performance of topsoil against horse manure in a study which investigated physico-chemical properties, erosion resistance, microbial activity, the kinds of plants grown and their density, and bare soil cover.
The study team used three different treatments across 15 plots on the north-facing embankment on a recently built embankment in Central Spain. They established and maintained the plots for 20 months.
The plots either received 10cm of fertile topsoil, 10cm of horse manure, or were left untouched as controls.
The horse manure had been collected from a nearby stud farm and comprised a 3:1 mixture of dung and pine shavings. It had been left in the open air for 8 months, from February to October.
The manure was found to be an effective alternative to topsoil for the improvement of soil fertility (organic matter content and total nitrogen). The topsoil and manure plots produced similar reductions in bare ground cover and erosion rates.
However, plots with topsoil showed greater soil respiration and species richness, with a different plant composition to the manure plot, which was closer to the control plots.
“These results suggest that manure can be used to replace topsoil to enhance embankment stability during the early stages of restoration,” they said. “However, if the aim of the restoration process is to promote plant diversity, topsoil is recommended.”
The results showed that horse manure could be a useful alternative to spreading topsoil if the aim was to improve variables related to soil fertility. The researchers concluded that manure was viable, depending on the objectives of the restoration project.
“The use of both topsoil and manure is recommended to accelerate restoration and revegetation of slopes during the early stages after linear infrastructure construction, when physical stabilization is a priority given the high erosion rates found on recently built embankments.”
Topsoil was recommended when restoration was aimed at increasing or maintaining the diversity of the local vegetation.
The study team comprised Peco and Desirée Rivera, from the Universidad Autónoma de Madrid; Pablo García-Palacios, from the Universidad Rey Juan Carlos; and Berta Jauregui, from Dirección Técnica.
Peco B, Rivera D, García-Palacios P, Jauregui BM (2017) Is manure an alternative to topsoil in road embankment restoration? PLoS ONE 12(3): e0174622. doi:10.1371/journal.pone.0174622