Data from more than 580 field experiments conducted in South Australia over the past 30 years have been re-examined to estimate extractable soil phosphorus (P) levels related to 90% maximum yield (C90) for 7 crop species (wheat, barley, oilseed rape, sunflower, field peas, faba beans, potato) and 3 types of legume-based pasture (subterranean clover, strawberry clover, annual medics). Data from both single-year and longer term experiments were evaluated. The C90 value for each species was derived from the relationship between proportional yield responsiveness to applied P fertiliser rates (determined as grain yield in crops and herbage yield in ungrazed pastures) and extractable P concentrations in surface soils sampled before sowing. Most data assessments involved the Colwell soil P test and soils sampled in autumn to 10 cm depth. When all data for a species were considered together, the relationship between proportional yield response to applied P and soil P status was typically variable, particularly where Colwell soil P concentration was around C90. When data could be grouped according to common soil types, soil surface texture, or P sorption indices (selected sites), better relationships were discerned. From such segregated data sets, different C90 estimates were derived for either different soil types or soil properties. We recommend that site descriptors associated with the supply of soil P to plant roots be determined as a matter of course in future P fertiliser experiments in South Australia. Given the above, we also contend that the Colwell soil P test is reasonably robust for estimating P fertiliser requirements for the diverse range of soils in the agricultural regions of the State. In medium- and longer term experiments, changes in Colwell soil P concentration were measured in the absence or presence of newly applied P fertiliser. The rate of change (mg soil P/kg per kg applied P/ha) appeared to vary with soil type (or soil properties) and, perhaps, cropping frequency. Relatively minor changes in soil P status were observed due to different tillage practices. In developing P fertiliser budgets, we conclude that a major knowledge gap exists for estimating the residual effectiveness of P fertiliser applied to diverse soil types under a wide range of South Australian farming systems.

In a series of 12 field experiments in 1990 and 1991, metsulfuron-methyl at rates of 2.1, 4.2, and8.4 g/ha (0.5, 1.0, 2.0 times the maximum recommended label rate of the commercial product) was applied at the early tillering stage to commercial barley crops in South Australia.At 4 sites, applications of 4.2 and 8.4 g/ha of metsulfuron-methyl resulted in a marked reduction in plant molybdenum concentrations for at least 6 weeks and grain yield reductions of about 10% resulted from applications of metsulfuron-methyl resulted in a temporary reduction in the concentrations of phosphorus and/or zinc for at least 4 weeks, followed by substantial recovery within 6 weeks. Temporary minor reductions in manganese, copper, sulfur, and potassium concentrations were also measured in the metsulfuron-methyl treatments at 3 sites. At harvest, no nutrient reduction due to chemical treatments was measured in grain samples from any site. Three weeks after the application of 4.2 and 8.4 g/ha of metsulfuron-methyl, marked decreases in total root length were measured in all diameter classes. We suggest these decreases are implicated in the plant these treatments. On these 4 sites and 5 others, nutrient reductions. Applications of metsulfuron-methyl at 4.2 and 8.4 g/ha resulted in grain protein increases of 0.3-0.4%, independent of yield.

In 11 experiments over 6 seasons the herbicide sethoxydim was applied to Machete, Spear and Blade wheat cultivars in the absence or near absence of weeds (10 sites) or where the weeds were controlled by selective herbicides (1 site), in the cropping area north of Adelaide, South Australia. The rates applied included 9-47 g a.i./ha at the 2-3 leaf growth stage and 9-74 g a.i./ha at early tillering. Except for the very long growing season of 1992, there was a highly significant positive linear correlation between the number of degree days in the growing season at each experimental site and relative mean yield increase of these sethoxydim treatments. Yield increases ranged from nil in growing seasons of about 1000 degree days to 32% in a growing season of 1480 degree days, with a median of 8% over the experiments.