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Enhancing buffel grass seed germination by acid treatment for rapid vegetation establishment on railway batters

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Abstract

Buffel grass (Cenchrus ciliaris) is one of the preferred species for revegetation of railway embankment steep slopes (batters) in Central Queensland, Australia. Its seed germination is inherently poor and becomes unpredictable, especially in semi-arid regions characterized by low rainfall, due to its extended period of dormancy. Thus its use for railway batters erosion control becomes a major concern where the development of good grass cover within a short time is required to minimize the risk of damage from storms. The effects of different germination media, and concentrations and soaking duration of sulphuric acid (H2SO4) on seed germination were evaluated.

Final seed germination without treatment was only 18%, 15% and 12% in the potting mix, heavy clay soil and Petri dish, respectively. Final germination percentage and velocity of germination was significantly greater with potting mix, followed by clay and paper towelling. Similarly, days to first germination, final germination and mean time to germination (MTG) were significantly earlier for potting mix, followed by clay and paper towelling.

Seed germination was highest (94%) on 4 min of soaking with concentrated H2SO4, and declined with extended soaking reaching to a lethal duration after 10 min. Seed germination was lower with lower concentration of the acid. Increasing acid concentration enhanced first germination, shorter duration for final germination and shorter MTG. At lower concentration also, increasing soaking duration beyond 20 min reduced final seed germination. Concentrated H2SO4 treatment may be employed for improving buffel seed germination provided safety issues for bulk handling are addressed.

Introduction

Soil erosion of railway batters (steep slopes) can evoke serious hazards; prolong interruptions of railway operations and also produce negative environmental impacts through off-site movements of sediments.

Bioengineering approaches are gradually becoming preferred practices to address railway batter erosion problem (Gyasi-Agyei et al., 2001; Gyasi-Agyei, 2003, Gyasi-Agyei, 2004a, Gyasi-Agyei, 2004b, Gyasi-Agyei, 2006). Revegetation of railway batters using appropriate grass cover has been suggested as a promising option (Gyasi-Agyei, 2004b) and its utility is now well established in some larger scale revegetation projects (Gyasi-Agyei et al., 2005).

Buffel grass (Cenchrus ciliaris L.) is a preferred species for erosion control of railway batters in the semi-arid regions of Central Queensland, Australia, due to its thick spread, quick regeneration and ease of maintenance. The species has a larger and deeper root system capable of providing greater strength against erosion than other grasses such as Rhodes (Chloris gayana L) and green panic (Panicum maximum var. trichoglume) (Harwood et al., 1999). The swollen stem base accumulates carbohydrates, allowing it to survive drought spells and to produce new growth after burning (Anonymous, 2006), and commencement of rain (Franks, 2002). The regenerative capacity of buffel grass after burning and drought hardiness makes it an ideal choice for dry communities and colonization of disturbed sites (Harwood et al., 1999). Buffel grass can provide an effective soil erosion control to railway batters provided a rapid vegetation establishment is achieved without delaying germination upon the formation of batter slopes. However, poor seed germination sown on railway batters due to inherent seed dormancy delays the development of good grass cover within a short time window and can result in poor control of soil erosion (Gyasi-Agyei et al., 2005).

Buffel is typically propagated by seeds. Its seeds can remain dormant for a considerable period of time before reaching maturity. Winkworth (1971) noted a protracted dormancy in buffel seed, which may last for 12 months or longer. Bulter (1985) suggested that dormancy mechanism lies within the caryopsis rather than in the associated structures of fascicle. However, Hacker and Ratcliff (1989), proposed buffel dormancy is partly caused by the fascicle, rather than just the seed dormancy, and possibly also an induced dormancy during the winter period also exist. Hence, as much as 50% of the sown seeds died in the field within 12 months of sowing (Silcock and Smith, 1990).

Various physical, mechanical, chemical and biological measures are utilized to overcome grass seed dormancy (Cook and Dolby, 1981). Bulter (1985) evaluated effect of pre-drying, potassium nitrate, and pre-chilling on relieving the dormancy. While pre-drying was useful in promoting germination (7–37%), pre-chilling had negative effects and potassium nitrate had no effects, suggesting very little commercial application of these treatments. Chemical treatment, such as sulphuric acid (H2SO4) was employed for seed dormancy breaking in other grass species (Gonzalez-Castaneda et al., 2004). Recently, Salehi and Khosh-Khui (2005) presented a remarkable increase in seed germination of four turf grass genera using H2SO4. Buffel grass may respond to H2SO4 treatment in the similar way, hence the aim of this study is to develop methods for enhancing buffel grass seed germination as its prolonged germination process in the batters increases the risk of seed washout by intense rainfall and consequently poor vegetation establishment. Different germination media, H2SO4 concentrations as well as durations were applied to buffel grass seed to improve germination for accelerating the revegetation of railway batters.

Section snippets

Materials and method

The experiments were conducted at the Central Queensland University, Australia (23°22′ S; 150°31′ E, altitude 90 masl) starting on 13 April 2005. A six month old seed lot of uncoated Gayndah buffel was sourced from a seed supplier. Seed samples for germination testing were taken from different parts of the bag to make a composite and final 1 kg batch. Sampling was carried out, given that seeds were selected in order to make each seed treatment batch similar based on weight. Each sample of 100

Results

In the first experiment, final germination percentage (Gp) and velocity of germination (VG) was significantly greater (P<0.05) with potting mix followed by clay and least with paper towelling. Likewise, days to first germination, days to final germination and mean time to germination (MTG) were significantly earlier for potting mix, followed by clay and least with paper toweling, respectively. Final seed germination of 18%, 15% and 10% at day 15 was recorded for the potting mix, clay and paper

Discussion

Seed dormancy is a challenge for revegetation with buffel in an arid zone (Rajora et al., 2002). Anthocyanins and phenolics in the seed coat as well as the hard seed coat inhibit germination. Scarification (Seiler, 1998; Sharif-Zadeh and Murdoch, 2001; Silcock and Smith, 1990; Thompson and Wildermuth, 1989), heat or smoke (Clarke and French, 2005; Muhammad and Amusa, 2003), and removal of glumes (Aliero, 2004) improves germination, but are inconvenient methods and also produce inconsistent

Acknowledgments

The authors acknowledge the support for this project by Queensland Rail, and CQU Australia. Our sincere thanks also go to Mr. Tim McSweeney for critically reading the manuscript and incorporating language corrections, and to two unanimous reviewers and editor for their creative comments.

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