2017 Plant, Soil and Environment Seminars
Friday 4th August 2017 In 1987, a group of entomologists from several institutions embarked on a long-term study of Helicoverpa ecology in non-cropping areas of inland Australia. This work has continued intermittently until this year, with funding from CRDC, GRDC, RIRDC, ARC and the Cotton CRC. We made a total of 79 field trips to the region, which encompassed inland areas of NSW, Qld, SA, WA and NT. Over 2000 sweep net samples for Helicoverpa spp. larvae have been made on over 230 different plant species, mostly natives. H. punctigera was by far the most common species, with 50.5% of samples yielding larvae. Only 4.2% of samples yielded H. armigera larvae, and these were mostly in the northeast of the study area. This is despite the fact that in the laboratory H. armigera larvae survive and grow well on some key inland hosts. H. punctigera larvae were found on 122 plant species from 18 families. Of these, 120 were new host records. Host suitability was assessed using the matrix of Zalucki et al. (1994; Aust. J. Zool. 42, 329), which plots relative incidence against relative abundance. The best hosts were annual daisies and legumes. Annuals from several other families were also commonly recorded as hosts. Perennial species were less suitable. Crops sampled around the margins of the study area supported fewer larvae than the native hosts, indicating the importance of native hosts in the continental population dynamics of H. punctigera. This thirty year study has provided a comprehensive picture of short and long term changes in host plant abundance in different inland habitats (floodplains, grasslands, acacia shrublands, chenopod shrublands, sandy deserts and stony downs). The Millenium Drought in 2001-2009 which severely affected southeast Australia (Van Dijk et al. 2013, Water Resour. Res., 49, 1040-1057) significantly affected host plant abundance in the acacia shrublands and to a lesser extent in the grasslands. Floodplains, sandy deserts, stony downs and chenopod shrublands were not affected. Host plants were recorded in about 61% of the sites surveyed in the acacia shrublands before the drought, and only in about 28% after the drought (P<0.001)). In the grasslands, about 49% of these sites supported host plants compared with 35% after the drought (P=0.018). The abundance of host plants also declined in many sites, and good hosts (such as the daisy Rhodanthe floribunda) were replaced by plants which supported fewer larvae (such as the Malvaceous plant Sida platycalyx). The impact of medium-term changes in climate, represented by the Millenium Drought, on Helicoverpa ecology, and the implications for management of these pests will be discussed. Wednesday 7th June 2017 Salt tolerant pasture species represent a valuable opportunity to intensify agricultural production in low-rainfall areas where saline land and or water (e.g. mine-site dewatering) are allocated to pastoral systems. Inherently variable in ionic composition and concentration, the response of plants to saline soils and groundwater are difficult to predict. Existing and novel approaches were applied to tropical and sub tropical pasture species to identify: mechanisms of tolerance to root-zone salinity; the individual effects of osmotic stress (OS) and osmotic stress and ion toxicity (OST) on plant growth and water use and; practical upper salinity limits for soil solution salinities. Generally, salt tolerant tropical and subtropical pasture species, including some glycophytes, should be considered for intensification of agricultural production in areas where root-zone salinity is an issue. The ability of glycophytic pasture species such as lucerne and leucaena to exclude Na+ at the root level, when root-zone Ca2+ was adequate, has potential value under root-zone salinity. However, if OST occurred, severe reductions in growth and plant water use were observed, potentially limiting glycophytes to situations where low soil solution salinities (2-5 dS/m) and adequate Ca2+ availability can be maintained. The capacity of halophytic Rhodes grass to safely accumulate ions to high concentrations in plant tissues at moderately high root-zone salinity (16 dS/m), whilst maintaining adequate plant growth and water use, meant it was the best option (of the species tested) for cultivation in tropical and subtropical areas affected by root-zone salinity. Biography Hayley is an agronomist and Lecturer in Tropical Agriculture at The University of Queensland. Her research interests range from the systems level of ruminant livestock production down to cellular processes, studying the physiological responses of pastures to abiotic stress. Hayley completed her PhD at the University of Queensland, studying the effects of root-zone salinity on plant production and water use of tropical and subtropical pasture species adapted to southern Queensland. She has experience in the intensive and extensive grazing systems of northern Australia, and agricultural research in South East Asia. Hayley has worked on a variety of research and extension activities associated with feed base improvement, plant breeding and toxicology. Monday 1st May, 2017 Analysing trial results often needs more than a simple anova. This presentation will outline some of the simple ways to check your dataset and the analysis to make sure that all the background assumptions are correct, and give examples of how to include spatial trends in the data analysis where it is needed. I will be using data from field trials as an example, but also from a pot trial in the glasshouse to highlight the fact that a glasshouse bay is definitely not a uniform growing environment, and that good trial design and analysis is vital for good results. Monday 20th February, 2017. Modern farming systems engage in less tillage and suffer from nutrient deserts in the subsoil. What root system characteristics should we aim for to move agriculture into the future and optimise nutrient recovery from increasingly ‘unnatural’ systems?
