Search

Aim: In Australia, natural grasslands largely occur on fertile clay soils and have consequently been extensively cultivated since European settlement. Other studies have demonstrated that passive restoration of subtropical grassland is possible in environments where there is substantial native remnant vegetation in the surrounding landscape. This study examined a chronosequence of abandoned fields to investigate the recovery of fragmented grassland in a matrix of cultivated land with significant exotic species that may impede succession. Location: Darling Downs, Queensland, Australia. Methods: In this study we surveyed a chronosequence of ex‐cultivated subtropical grasslands in Queensland's Darling Downs, where only 1% of the original grasslands remain. Floristic surveys were carried out in 80 fallow sites up to 51 years old, and data were compared with 16 previously surveyed remnant grasslands on the same land type. Results: Richness of native species increased with time since cultivation and approached, but did not reach, that of remnant grasslands after 51 years, whereas the richness of exotics declined with time since cultivation. Rainfall and grazing positively and negatively affected exotic plant abundance respectively and these factors had no significant direct or indirect effect on the native species richness. In terms of composition, fallow grasslands supported 54% of the native plant species from remnant grasslands after 51 years. The native perennial grasses Dichanthium sericeum and Aristida leptopoda were the only dominant species in the remnants that were present in more than 60% of the fallow grasslands. Of the species from remnants that were "missing" from fallow sites, most were native perennial forbs and grasses. Compositional dissimilarity of fallow grassland to remnant grasslands remained high after 51 years (78%). Grassland species that are uncommon in nearby hill woodlands were preferentially absent in fallow grassland and this partly explains the slow compositional recovery. Conclusion: In a highly fragmented landscape, passive restoration is only partially effective. The restoration of grassland is probably enhanced by repositories of native seeds from hill woodlands that are too rocky to cultivate. However, some species may have to be actively reintroduced to achieve complete recovery. In this landscape, where grazing is a dominant land use, exotic species do not seem to impede succession. [ABSTRACT FROM AUTHOR]

Abstract Chickpea is susceptible to water logging and responds to soil aeration. Oxygen deficiency at both a temporal and spatial scale could occur for a subsurface drip irrigated crop, particularly in heavy clay soils. Use of aerated water irrigation (oxygation) to overcome hypoxia in the rhizosphere was evaluated in broad-acre chickpea crops in 2006 and 2007, in a heavy clay soil of central Queensland, Australia. The injection of 12% by volume air into subsurface drip irrigation water (oxygation) to two consecutive broad-acre chickpea crops resulted in a beneficial effect on yield (gains of 27% and 10% for 2006 and 2007, respectively), but the effect of irrigation regimes at deficit and full irrigation (85 and 100% ETc) was not significantly different. Chickpea yield with aerated subsurface drip irrigation was much higher (3.24 and 2.05 t ha-1) compared to the 7-year (2008–2015) national average yield (1.13 t ha-1). The aerated irrigation resulted into significantly higher gross production water use index (GPWUI) and irrigation water use index (IWUI) particularly in the year when the crop was planted early in the season. There was no significant difference in response to either of these water use efficiency (WUE) indicators between irrigation treatments, with the exception of a significantly enhanced IWUI with the 85% ETc in the first season. These results were consistent with those for cotton on the same site, providing further justification for the capital investment required for oxygated subsurface drip irrigation (SDI) system. Highlights • Aerated water for sub-surface drip irrigation improved chickpea yield by 10–27% compared to the control. • Chickpea yields with subsurface drip irrigation were 81–187% higher than the national average of 1.13 t ha-1. • Aerated water irrigation increased gross production water use index and irrigation water use index for chickpea in a Vertosol. [ABSTRACT FROM AUTHOR]

A large part of Australia's broad acre irrigation industry, which includes cotton, is farmed on heavy clay Vertosols. Recent changes in nematicide chemical availability, changes in rotations and the observation of the reniform nematode in central Queensland has highlighted that we need to improve our understanding of nematodes in these soils. We undertook preliminary investigations into distribution by depth under a cotton-cotton and cotton-maize rotation as well as vertical movement experiments in microcosms to better understand nematode distribution and movement in heavy clay soils. Analysis revealed that field populations decreased with soil sample depth, but there were also differences between rotations. In microcosm experiments, vertical movement of nematodes in these heavy clay soils was restricted, even in the presence of plant roots and moisture, both of which were hypothesised to improve nematode migration. The results imply that crop rotation currently remains a plausible option for nematode control, and that we still have a lot to learn about the ecology of nematode populations in Vertosols. [ABSTRACT FROM AUTHOR]