In the selection of acid-tolerant Rh&obium meliloti, procedures for the collection and isolation of rhizobia, and the assessment of acid tolerance, have not been critically evaluated. Such procedures form the basis of this study. Root nodules were collected from Medicago spp. found growing on acid soil in Sardinia. Their encumbent bacteria were isolated directly onto media adjusted over a range ofpH values, and then assessed for acid tolerance in both the laboratory and field. Strains of Rh&obium meliloti isolated onto low pH media were, in general, more acid-tolerant than sister isolates from high pH media, when tested in both the laboratory and field. Dilution (10 or 100 fold) of the inocula used in the laboratory assessment did not greatly influence the rating derived, although there was some effect of bacterial colony type on growth rating. The link between polysaccharide production and acid tolerance was not strong. There was a poor correlation between the growth ratings derived from the laboratory screening and acid tolerance as expressed in the field.

During consecutive seasons, wild radish (Raphanus raphanistrum L.) seedling emergence decreased exponentially with increasing time after the emergence of lupin crops. Initial survival of seedlings was markedly reduced by pre-emergence applications of simazine at 0.75 kg a.i. ha-1. In the absence of herbicide, however, the presence of a lupin crop did not have a negative effect upon early survival. Probabilities of reproduction of wild radish plants decreased with later emergence within treatments; no plants which emerged later than 21 days after crop emergence produced seeds. Seed production by wild radish was considerably higher when lupins were sown late. Regardless of sowing date, the application of triazine herbicides reduced the amount of seeds produced to the point where grain contamination was insignificant. However, the few plants which escaped herbicide treatment produced large numbers of seeds. Virtually no seeds were produced when additional post-emergence applications of simazine (0.375 kg a.i. ha-1) were made. It is argued that the major role of post-emergence application in this crop-weed system is to prevent reproduction by plants which escape the pre-emergence application, rather than to control late-emerging plants.

Three cultivars of wheat were grown using five levels of applied nitrogen (N) fertilizer at five locations in the central wheatbelt of Western Australia during 1986, 1987 and 1988. The cultivars were Gamenya (old, tall), Gutha (new, tall) and Aroona (new, semidwarf). The aim of the experiments was to determine if the newer cultivars responded more to applied N fertilizer than the older ones. At 10 out of 15 sites there was a yield increase to applied N. The semi-dwarf cultivar Aroona out-yielded the two tall cultivars apd responded more to added N at 6 of the 15 sites. The average initial response to applied N at these six sites was 16, 18 and 31 kg of grain per kg of N applied for Gamenya, Gutha and Aroona. Aroona's increased initial response to applied N was not evident at five of the sites that received less than 250 mm of rainfall during the growing season. The increased responsiveness of Aroona was associated with a greater apparent net uptake efficiency, a larger concentration of N in the tops, the production of more ears and kernels per unit area at larger concentrations of N in the tops, and an ability to maintain kernel size at the larger kernel numbers produced by an increased N supply.

Anecdotal observations suggest that pigs get fatter at certain times of the year. Abattoir data from a major Western Australian genotype were investigated to determine whether there is seasonal variation in P2, and if so, what factors may contribute to this. In the data collected, it was found that pigs were fattest during spring and leanest during autumn. At initial observation, variation in carcass weight (hence liveweight at slaughter) appeared to explain much of the variation in carcass fatness. However, fitting a linear mixed model to the P2 data, adjusted for carcass weight, indicated that there was also a significant effect of season on carcass quality.

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