Severe leaf blotching in a crop of barley growing on a red-brown earth (Calcic Rhodoxeralf) was closely associated with high concentrations of boron in the soil. No infection by fungal pathogens capable of accounting for the symptoms was found. Of 14 elements determined in the plants only accumulation of high-concentrations of boron was associated with the disorder. Boron concentrations in saturation extracts of subsoil ranged up to 17.9 �g boron/cm3 under plants that were severely affected, and plants sampled just prior to anthesis contained up to 96 fig boron/g (mean 62.4). Plants that were only slightly affected contained less than 15 �g boron/g (mean 13.8). Grain yield was depressed by 17% due to the boron toxicity. This is only the second report of boron toxicity due to naturally occurring boron in Australia, and the first for a red-brown earth.

No abstract

Soil types, cereal crop growth and grain yields are typically variable across many paddocks in the cropping regions of South Australia. In this study the value of a variable rate nitrogen fertiliser application, using the Yara N-Sensor, was compared with the standard practice of a uniform application, at crop growth stage 31, on the grain yield and protein content of wheat. These comparisons were made using the same total amount of fertiliser in paired variable and uniform rate treatments in commercial crops at a total of 10 sites over two years in the medium to higher rainfall areas of the Mid North and Yorke Peninsula of South Australia. The mean increase in wheat grain yield for the variable rate treatment was only 40 kg/ha, or 0.8%, when compared with the uniform rate treatment averaged over these 10 sites and two years. Grain yield differences ranged from 160 kg/ha more to 60 kg/ha less for the variable rate treatment when compared with the uniform rate treatment. Wheat grain yields with the uniform treatments ranged from 2.53 t/ha to 5.68t/ha and with a mean grain yield of 4.24 t/ha. The mean wheat grain protein content with the variable rate treatment was 11.0%, compared with 10.5% with the uniform rate treatment, a relative increase of 5.1%. Where grain yield responses to the variable rate treatments were compared between different biomass areas within a paddock, the greatest grain yield increases to a variable rate of N compared with a uniform rate were in the areas with the lowest 20% of crop biomass whereas grain yield differences were negligible in areas with the highest 60% of crop biomass. These low biomass areas also had the greatest grain yield response to the applied post emergent nitrogen fertiliser when compared with areas with no post emergent nitrogen fertiliser. N-Sensor outputs (biomass and N-rate) were compared with measurements of plant biomass, N uptake (kg N/ha) and %N content at points of contrasting biomass and N-rate within paddocks. There was a high correlation between the N-Sensor biomass and N-rate values and actual plant biomass and N uptake but not with the %N content. Crop biomass maps made using sensors such as the N-Sensor could provide useful data layers, which in combination with other datasets such as grain yield maps or elevation maps, be used to produce zone maps for further analysis or for variable rate input treatments. The N-Sensor could also be used in some situations to map variations in weed biomass for possible site specific weed management.

The ability of Rhynchosporiurn secalis to survive over summer in plant debris and to produce inoculum for scald disease development in barley crops was investigated. Viable inoculum was recovered from dead host leaves (Hordeurn vulgare and H. leporinurn) kept on soil surfaces in the field for up to 30 weeks after crop maturity in a range of South Australian barley-growing environments. When infected leaves were suspended 30 cm above soil surfaces, the fungus survived for up to 37 weeks. When buried 6 cm below soil surfaces, the fungus survived for 20 weeks. Following an initial decline in infectivity of inoculum over summer, infectivity increased during autumn to levels similar to those obtained at the start of the trials.

The potential commercial use of fungicides for control of stem rust (Puccinia graminis) of wheat was assessed in field experiments at two sites. Foliar sprays containing either triadimefon or propiconazole were the most effective in reducing disease severity. Chlorothalonil was effective only when applied at an early stage of disease development and where stem rust was not severe in control plots. Dichlone, fenarimol, nuarimol and 2-(thiocyanomethylthio) benzothiazole did not significantly reduce stem rust severity at either site. Even though treatments were applied at an early stage ofthe disease epidemic at one site, disease control on heads, peduncles and sheaths did not exceed 63,36 and 19%, respectively, with any treatment. Increases in grain yield and density, of up to 0.27 t/ha and 8.6 kg/hectolitre, respectively, were barely sufficient to cover the cost of treatment.