Long-term persistence of aluminium-tolerant and sensitive Phalaris lines on acidic soils and associated changes in soil acidity

Abstract

Persistence of an aluminium (Al)-tolerant phalaris F1 hybrid (Siro 1146 Phalaris aquatica × P.�arundinacea) was compared with that of 3 more Al-sensitive phalaris (P. aquatica L.) lines (cv. Australian and the progenitors of cvv. Sirosa and Sirolan) at 2 sites (Strathbogie and Baddaginnie) in north-eastern Victoria with strongly acidic soils 20 years after sowing. Soil pHCa and extractable aluminium (AlCa) were also measured to 1 m depth under Siro 1146 and annual grass pasture at each site. All grass treatments contained volunteer subclover. Siro 1146 persisted better than the other lines (P<0.05) at Strathbogie where the soil contained high AlCa concentrations down to 50 cm depth. Soils should be sampled and tested to at least this depth to determine their suitability for phalaris. At this site Australian phalaris persisted better than the progenitors of Sirosa and Sirolan (P<0.01), probably because Australian has more spreading ability and tolerance of set stocking than the winter active lines. At Baddaginnie, the soil contained lower concentrations of AlCa below 20 cm depth than at Strathbogie and persistence of the 3 Al sensitive phalaris lines was good despite the lower rainfall. The less drought-tolerant Siro�1146 persisted poorly at Baddaginnie, but had high ground cover due to high lateral spread of the survivors. At Strathbogie, the 10–20 cm layer of soil under Siro 1146 had a higher pHCa and lower AlCa than that under the other 4 phalaris and the annual grass treatments. Soil under Siro 1146 also had higher pHCa and lower AlCa down to 40�cm�depth compared with the annual grass treatment, the differences being significant in the 20–30 cm layer. These differences were reversed at 50–100 cm, but only the effect on Al was significant. Although soils were not sampled at the beginning of the experiment, adequate replication and randomisation of the grass treatments showed that it was statistically improbable for observed final differences to be due to initial soil differences. The final differences may be due to greater amounts of nitrate being taken up from the upper layers by Siro 1146 over its long growing season compared with the annual grasses, leading to greater nitrate leaching from the upper layers and greater nitrate uptake from lower layers under the annuals (i.e. spatial separation of acid generation and consumption processes within the profile). Another possible reason for the greater acidification below 50 cm by the perennial is that its roots may have taken up more cations in this zone. Because of rising concern in some sectors of the public about the off-site, environmental effects of agriculture, the future role of more acid-tolerant phalaris cultivars growing near native vegetation in the high rainfall zone is discussed.

Progress in improving aluminium tolerance in the perennial grass, phalaris

“…Australian type of phalaris, represented here by cv. Australian II, is often more persistent on acid soils than other cultivars (Ridley et al, 2002). These results suggest that this is not due to higher Al tolerance.…”

“…An F 1 hybrid between the two species (cv. Siro1146) was much more persistent than cultivars of P. aquatica on a deep acid soil (Ridley et al, 2002) but has seed production and palatability problems. Oram et al (1990) developed a P. aquatica × P. arundinacea × P. aquatica backcross population to introgress genes for Al tolerance from P. arundinacea into a P. aquatica plant type.…”

Field Evaluation of Cocksfoot, Tall Fescue and Phalaris for Dry Marginal Environments of South‐Eastern Australia. 2. Persistence

“…and phalaris ( Phalaris aquatica L.) are the major perennial grasses of sown permanent pastures in areas of the high rainfall zone (>600 mm) of south‐eastern Australia considered too dry for perennial ryegrass ( Lolium perenne L.), where they are valued for their forage production, drought survival and environmental benefits such as reducing the rate of ground water recharge and soil acidification (Ridley et al. , White et al. ).…”

“…Darbysh.) and phalaris (Phalaris aquatica L.) are the major perennial grasses of sown permanent pastures in areas of the high rainfall zone (>600 mm) of south-eastern Australia considered too dry for perennial ryegrass (Lolium perenne L.), where they are valued for their forage production, drought survival and environmental benefits such as reducing the rate of ground water recharge and soil acidification (Ridley et al 2002, White et al 2003. These species have the potential for similar benefits in the mixed cropping/livestock zone where they could also address the low ground cover of lucerne (Medicago sativa L.; Dear et al 2007) and offer a novel option for winter feed production in phased cropping rotations (Hackney et al 2006).…”

Recurrent selection for grazing tolerance in winter-active populations of the perennial grass, Phalaris aquatica L.

“…The CSIRO phalaris breeding program has released several 'winter-active' cultivars with higher seedling vigour and productivity in the cooler months compared with 'semi-winter dormant' cultivars (Oram and Culvenor 1994). However, present winter-active cultivars are perceived as being less persistent under heavy grazing pressure (Kemp and Dowling 2000) particularly when associated with soil acidity (Ridley et al 2002). The breeding program currently aims to improve phalaris persistence through projects on grazing tolerance, soil acidity and tolerance of hotter, more drought-prone environments.…”