It's widely known that plant roots and rhizomes assist in strengthening soil, and can also aid in erosion control. However, until recently hardly any research has been done with regard to which plants strengthen the soil better than others, and the research that was conducted, only focused on a very small sample of plants.
The purposes of this investigation, is to test the influence 31 different commonly used landscape plants, and three commonly used erosion control turf varieties have on soil shear strength.
The different varieties were chosen from the most regularly used Australian erosion control landscape plants and turf types. Many of these plants and turf types are also used in the USA, Europe, and Asia. A lot of improved varieties were also included, as they're widely used in Australia, and it allowed this investigation to test the improved varieties compared with the common forms from the same genus and species.
10 large sample pots for each variety were grown and tested with the use of a Shear Vane tester, just as samples were grown in two completely different gardens, and replicated turf plots. 29 shear vane tests were taken for each variety from the pots.
Compared to the control samples of unvegetated potting mix and soil, the results showed that all plants strengthened the soil. Increases in soil shear strength were analysed using an ANOVA test.
Any variety that showed a 95% or more increase in shear strength was found to be significantly different to the unvegetated samples. King Alfred, an improved variety of Dianella caerulea was found to have more than doubled the soil strengthening ability, compared to all other plants, other than Nafray, which was still well below King Alfred.
King Alfred strengthened the soil 752%, and in this test had an undrained shear strength of 70 kPa, compared to unvegetated soil of 9 kPa. Many other varieties however, still strengthen the soil greatly. Katrinus Deluxe, a Lomandra longifolia, strengthened the soil by 366%.
Plants such as Liriope Evergreen Giant (widely used in the USA and Australia), had much lower readings, only strengthening the soil a statistically significant 100%.
Varieties that have been improved through breeding, all strengthen the soil considerably more than their corresponding common varieties, providing evidence that plant breeding can lead to plants better suited to strengthening soil.
Empire Zoysia Turf strengthened the soil significantly, at a rate of 97.9 kPA, considerably more than Couch 68.1 kPa (Bermuda grass) and Kikuyu 72.4 kPa.
This data can help Engineers, Landscape Architects, and Erosion Control professionals choose plants and turf that better strengthen the soil, and enhance erosion control of slopes, batters, stream embankments, roadsides, retaining walls, and shore lines. It will also provide a basis for future plant breeders to develop plants and turf that better strengthen the soil.
For more details from this erosion control plants and turf types research click here: http://www.ozbreed.com.au/research-papers/erosion-research.html and to contact Ozbreed directly please visit http://www.ozbreed.com.au/contact.html