Megan Ryan

Ptilotus polystachyus (green mulla mulla; ptilotus) is a short-lived perennial herb that occurs widely in Australia in arid and semi-arid regions with nutrient poor soils. As this species shows potential for domestication, its response to addition of phosphorus (P) and nitrogen (N) was compared to a variety of the domesticated exotic perennial pasture herb Cichorium intybus (chicory), 'Puna'. Pots were filled with 3 kg of an extremely nutrient-deficient sterilized field soil that contained 3 mg kg(-1) mineral N and 2 mg kg(-1) bicarbonate-extractable P. The growth and P and N accumulation of ptilotus and chicory in response to seven rates of readily available phosphorus (0-300 mg P pot(-1)) and nitrogen (N) (0-270 mg N pot(-1)) was examined. Ptilotus grew extremely well under low P conditions: shoot dry weights were 23, 6 and 1.7 times greater than for chicory at the three lowest levels of P addition, 0, 15 and 30 mg P pot(-1), respectively. Ptilotus could not downregulate P...

ABSTRACT The impacts of broadleaf crop, pasture or fallow breaks within cereal-based cropping systems are widely acknowledged, but most studies have focussed on the first cereal crop after the break. We report a series of four field experiments in a semi-arid cropping zone of Southern Australia in which the impacts of a range of Year 1 sequence options (crops, pasture and fallow) on Year 3 and 4 wheat crops were investigated. In three of the experiments, two phases of the same experiment were commenced in successive years, providing seven sequence phases. In three of the seven phases (at three of the four sites), the Year 1 treatments influenced the yield of Year 3 or Year 4 wheat crops by 0.6, 0.9 and 0.9 t ha−1, although different responses between phases of the same experiments at two sites provided clear evidence of significant seasonal interactions. Interactions of Year 1 sequence treatments with tillage, crop species/varieties and/or added P-fertiliser treatments in intervening years also occurred at some sites. The largest persistent yield impacts related to the preservation of differences in residual nitrogen (N), and in some cases water following Year 1 crops through subsequent dry seasons, which were frequent in most experimental phases. Higher residual N levels after legumes and canola could persist for 2–3 years and induce yield penalties due to “haying-off” when Year 3 or 4 wheat crops experienced dry spring conditions. Such effects were offset following Year 1 fallow due to increased residual water at depth. Increases in the cereal root diseases take-all (Gaeumannomyces tritici) and rhizoctonia (Rhizoctonia solani AG8) due to Year 1 wheat also persisted through dry seasons and reduced Year 3 wheat yield in some experiments. We found no evidence for a significant role for arbuscular mycorrhizal fungi in yield of Year 3 and 4 wheat crops. We demonstrate that large and significant yield impacts (>0.5 t ha−1), both positive and negative, can persist for 3–4 years in semi-arid environments as a result of water, N and disease inoculum legacies of Year 1 crop sequence choices. Prolonged dry periods help to preserve these legacies, so that persistent and unpredictable crop sequence effects will be a feature of cropping systems in semi-arid areas with variable climates.

Native Australian perennial herbaceous legumes with potential to be developed as pasture plants for the medium-low rainfall zones of the wheatbelt were collected and screened. The aim was to identify species with characteristics suited for domestication and adaptation for difficult environments, such as highly acid soils, poorly fertile soils, and areas with low rainfall or prone to drought. A literature

ABSTRACT Subterranean clover (Trifolium subterraneum) is a key pasture legume across southern Australia and elsewhere. Decline in subterranean clover pastures was first recognised in Australia during the 1960s and manifests as an increase in weeds and a decrease in desirable legume species. While both root disease and poor nutrition contribute to subterranean clover pasture decline, the relationships between root disease and nutrition have not been determined. The objective of this study was to define these relationships. Field experiments were undertaken to determine the nutritional and pathogen status of soils and subterranean clover from three Western Australian field sites. Subsequently, controlled environment experiments were undertaken to determine the relative severities of tap and lateral root disease and growth of plants when soil cores taken from these three field sites were amended with a complete nutrient solution or a range of individual macro- or micronutrient treatments. Application of a ‘Hoaglands’ complete nutrient solution decreased the severity of tap root disease by an average of 45% and lateral root disease by 32%. Amendment with K alone reduced the severity of tap root disease an average of 32%; while the application of N alone reduced the severity of tap root disease by 33% and lateral root disease by 27%. Application of Hoaglands, K, N or Zn increased shoot and root dry weight, while Mo only increased shoot dry weight. This is the first report to show that mineral nutrients can substantially ameliorate root disease in subterranean clover. The results demonstrate that while root disease limits plant growth, improvement in the nutritional status of nutrient-impoverished soils can significantly reduce root disease. There is significant potential to incorporate nutrient amendments into an integrated and more sustainable approach to better manage root disease and to increase productivity of pasture legumes where soils are inherently nutrient deficient in one or more nutrients.