Evaluation of Different Seed Mixtures for Grass Establishment to Mitigate Soil Erosion on Steep Slopes of Railway Batters

Unpredictable rainstorms can pose greater risks of soil erosion on newly formed unprotected railway batters. A bioengineering approach consisting of revegetation can be an effective tool for soil-erosion control. Perennial species, such as buffel grass, are preferred for durability of vegetation cover in the arid and semiarid tropics. However, it takes a longer time to establish buffel than annual species such as Japanese millet (JM). A replicated plot-scale field trial consisting of different proportions of grass-seed mixtures of buffel and JM was conducted on railway-batters slope in the semiarid tropics of central Queensland, Australia. A supplementary automated drip irrigation system was set up to aid seed germination and early establishment of the grass cover. JM alone or JM-dominated seed mixtures significantly reduced soil erosion during the earlier stages. For example, during the second sampling interval (SI), which occurred 63 days after seeding, JM alone reduced soil erosion by 50% (20.2 versus $10.21\mathrm{t}/\mathrm{ha}$) in comparison to the sole buffel. This trend began to shift as the growth of buffel commenced at the latter stages. By the end of the 11 months, erosion from all seeded plots was not significantly different among the plots with more than 90% soil-loss reduction in comparison to the bare scenario, resulting in more than 60% grass cover. Results suggested that a monoculture of JM or JM-dominated seed mixture with buffel grass could be an effective bioengineering approach for revegetation of railway batters for protection against soil erosion. Quick establishment owing to faster seed germination, seedling establishments, and growth-producing sizable canopy cover developed by JM in the early stage of batter could reduce soil erosion in comparison to a sole crop of slow-growing perennial species buffel. The established vegetation self-regenerated and responded dynamically and naturally to changing conditions of the railway batter within a year, after which JM started to die back.