Distribution and abundance of annual legume seeds in the wheatbelt of Western Australia

Abstract

The size and composition of pasture legume seedbanks were estimated from 2 surveys on a 460-km west-east transect of the wheatbelt of Western Australia. Survey 1 (in spring) sampled naturalised legumes, and survey 2 (in summer) measured the amount and botanical composition of legume seed from selected sites. Seedbanks were examined in greater detail on 2 farms in the higher rainfall part of the wheatbelt. Survey 2 revealed that mean seedbank size of the poorest 40% of sites (those with 5200 kg seed/ha) was 61 kg/ha, and that 72% of seeds were naturalised clovers. In contrast, the best 60% of sites (those with >200 kg seed/ha) averaged 533 kg seed/ha, of which only 35% was naturalised clover seed, the remainder in both surveys being mainly subterranean clover (Trifolium subterraneum). Mean seed bank size (kg/ha) varied from 359 (survey 2) to 587 (survey 1) and, in both surveys, was poorly correlated with long-term mean annual rainfall and a number of soil parameters. On the 2 farms, seedbank size ranged from 300 to 345 kg/ha (in spring) and from 650 to 740 kg/ha (in summer). Trifolium glomeratum (cluster clover) and subterranean clover were the most widespread species in both surveys. They were present at 35 and 30 of the 57 survey sites, respectively, and at both farms. Most of the subterranean clover collected was cv. Geraldton (22 of 30 sites), the next most frequent cultivar was Dwalganup (6 sites). The currently recommended cultivar, Dalkeith, was found at only 5 sites. Several other legumes including T. tomentosum (16 sites), T. suffocatum (8 sites), Medicago truncatula (7 sites), T. hirtum (4 sites), and M. minima (4 sites) were common, while M. littoralis, M. polymorpha, T. dubium, T. cernuum, T. cherleri, and T. carnpestre were found at single sites. With few exceptions, these are naturalised species and were characterised by flowering times about 20 days later than sown legume cultivars, and seed sizes < 1 mg. The value of these widespread annual legumes to agricultural productivity and sustainability needs to be quantified and their adaptation to wheatbelt farming systems assessed.

Assessment of genetic diversity in clover species from Sardinia, Italy, using AFLP analysis

“…Imam and Allard 1965, Crawford et al 1998, Green et al 2001 and it is suggested that these populations are more likely to have lower levels of genetic variation within populations because only a limited number of individuals would have contributed to the population (Hamrick 1982, Bennett 1999. Therefore, one reason that the inbreeder T. glomeratum was found to contain higher levels of withinpopulation variation than expected is because the populations were taken from the speciesÕ native environment rather than in colonizing environments where it has previously been studied (Fortune et al 1995, Bennett 1997.…”

“…(hop clover). The naturalized clovers have adapted well to their naturalized environments and have been found to contain relatively large amounts of genetic variation both within and between populations (Fortune et al 1995, Bennett 1997. Although within-population genetic variation is still greater in their native environment (Bennett 1999), some species, such as T. subterraneum, have been shown to contain almost as much variability in Australia as the original Mediterranean populations (Cocks 1992).…”

Do some naturalised legumes have the potential to improve pasture production in the Victorian Mallee?

“…Naturalised legumes (not commercialised or deliberately sown) are widely distributed and have some adaptive advantages, such as high levels of hardseededness and a small seed size, which promote their persistence under grazing and through cropping phases. Naturalised legumes can comprise the bulk of the pasture seedbank (Fortune et al 1995) although their contribution to herbage biomass production has not been evaluated and quantitative information on the morphology and nutritive value of some species is scarce. The prominence of naturalised species in areas previously sown to commercial species warrants investigation of their value as components of pastures.…”

“…M. minima is widely distributed throughout Australia and grows in a wide ecological range (Bennett 1999), while T. arvense is found growing in infertile, sandy soils (Palmer 1972) and may also be widely distributed across Australia (Fortune et al 1995). There seems to be nothing known of the agronomy of M. monspeliaca, while M. minima and T. arvense are usually described as colonising species (Palmer 1972;Cocks 1999).…”

The use of spatial analysis to measure the effect of environmental heterogeneity on genetic variation in Trifolium species from Sardinia

“…Traditionally the Mediterranean region has also been the centre of domestication and breeding of most of the cultivated species of Trifolium, particularly the perennial clovers, although it can be argued that Australia has also become an important region for Trifolium breeding, with many new species being developed as pasture cultivars (Snowball et al 1992;Nichols et al 1996). In Australia there are also many naturalized species of Trifolium, and a study by Fortune et al (1995) found that wherever they occurred in the wheatbelt of Western Australia they contributed more seed to the seedbank than the sown pasture species. They have become adapted to a wide range of edaphic conditions in southern Australia, due largely to the genetic diversity within each species, even within individual populations (Cocks 1992 in T. subterraneum; Bennett 1997 in T. glomeratum; Bennett 1999 in T. tomentosum).…”