A growth disorder of cotton ( Gossypium hirsutum) occurs in irrigated cracking clay soils in cotton growing regions of northern New South Wales. Observations of early season cotton growth were made at l 00 m intervals along transects in fields that showed gradients in severity. Ordination analysis of physical and chemical properties of the soil distinguished three groups of sites (A, B, and C) which corresponded to patterns of yield and early season growth. Early season growth and arbuscular mycorrhizal colonisation of cotton at group A and B sites was much slower than at group C sites. Group B sites showed a recovery of yield later in the season while group A sites did not. Group A and B soils had lower pH, finer texture and higher P, Zn, Mn and exchangeable Mg, K and Na than group C soils. Thus, paradoxically, the greatest stunting occurred in the more fertile soils with putatively more favourable pH for cotton growth. Shoot growth also decreased with increasing manganese availability, soil clay content and soil water holding capacity. The stunting of seedlings at an early stage was not consistent with some potential physical and chemical causes of stunting, including sodicity, compaction, manganese toxicity and waterlogging. Cotton had a high relative field mycorrhizal dependency in group C soil (up to 92% at six weeks after sowing). A series of bioassays in pots showed that slow mycorrhizal development in group A soils was not due to a reduction in the number of propagules of mycorrhizal fungi. Cotton was less dependent on mycorrhizal fungi in group A soils (15 to 20 % ), which partly accounted for the lower levels of colonisation, but the soil microflora also inhibited mycorrhizal development. Sterilisation of group A soils consistently eliminated root browning, a symptom of the disorder, and increased cotton growth in pots and in the field. This was despite the negative effects of sterilisation on P and Zn nutrition due to the elimination of mycorrhizal fungi. Fungi, viruses and nematodes were discounted as possible pathogens. Soil borne bacteria were shown to be causal because (i) cotton growth was increased by the application of streptomycin and penicillin, (ii) bacteria were observed in and streaming from browned cotton roots and (iii) bioassays showed that a species of fluorescent Pseudomonas isolated from cotton roots was pathogenic to cotton. Variation in cotton growth within fields could be accounted for by the additive effects of nonbiological and biological properties of the soil, including both beneficial and pathogenic microorganisms

Two fields of cotton on two nearby farms in the Macquarie Valley of NSW which had different histories of weed management were studied to determine if weed seeds were being introduced via irrigation water. The experiment was set up as a randomised block design with five rows on each fann studied. At the beginning of each irrigation, traps constructed from wire gauze with holes of approximately 1.5 mm diameter were placed over the outflow end of each of the siphons feeding the selected rows. At the beginning of the season soil samples were taken from the furrows of the selected rows to determine the size of the weed seed bank in each field prior to irrigation.

A paper was presented at the fourth international Trichogramma and other egg parasitoid conference titled 'Evaluating egg parasitoids for integrated pest management in Australian raingrown cotton.' Highlights of papers presented at the conference and of discussions with researchers are presented below

The comparative advantage1 of cotton production was examined for three production systems in the United States and four production systems within Australia. Operating expenses, income, operating margin and machinery fixed costs are presented. Tax, social structure, subsidies and capital investment differences are also discussed. Sensitivity analysis was conducted varying the exchange rate and crop yields. Conclusions were drawn on the competitive advantages of investing in cotton production in Australia versus the US

Objectives of visit: To attend the 13th Conference of the International Soil Tillage Research Organization (ISTRO) and present paper entitled "Effect of soil preparation method and cotton-based cropping system on seedbed soil properties in a Vertisol". To have discussions with scientists conducting research on sustainable tillage and cropping systems. In the short-tenn their comments will be utilized in improving and analyzing on-going trials of cotton-based rotation systems on "permanent beds" funded by the Cotton Research and Development Corporation (CRDC) as Project DAN 83C.

The inaugural Australian Rural Leadership Program was conducted during 1993 and 1994.The rationale for this innovative concept was to form a strong bond between the 30participants, enrich their leadership capabilities and establish a leadership network. Theprogram brought together a diversity of rural background, and set in place a foundationfor succeeding graduates to extend the network for the betterment of rural Australia.rm

With CRDC permission, the travel award was transferred from Dr Skerritt to Ms A Hill, the diagnostics project leader; there was, however, not a change in itinerary. The major activities undertaken were: attendance at the Eighth IUPAC International Congress of Pesticide Chemistry (Washington, DC, USA; July 4-9) and a visit to the laboratories of Prof Bruce Hammock and Dr Alex Karu (University of California, Davis and Berkeley, respectively; July 11-14). The IUPAC meeting had several sessions that were particularly relevant to our current research on the development of immunoassay kit methods for pesticide analysis in environmental and food samples, including: pesticide dissipation in plants and soil; biotechnology- based analytical methods; ecological risks in relationship to pesticide chemical properties; fate of pesticides in water, soil and air; pesticide binding in soil and sediment; and both current and new methods in residue extraction and analysis in environmental and food samples. We presented a paper describing our work on test kit analysis of endosulfan and metabolites in cotton environments. Attendance at the meeting benefited our work through obtaining first-hand information on synthetic strategies for pesticideprotein conjugates, water and soil sample preparation and extraction for immunoassay. The laboratory visits were especially valuable for research related to our CRDC and Cotton CRC objectives, on development of: synthetic strategies for pesticide-protein coupling, sample extraction and analysis, and establishment of a new method for production of pesticidespecif ic antibodies, namely the expression of recombinant antibodies in E. coli.

The objective of this study was to examine the distribution of tyre imposed stresses, soil displacements and soil mechanical properties as function of the soil surface geometry. The study was performed using the advanced soil bin facility at Silsoe College (Cranfield University), England. Valuable experience was gained in using this type of equipment (which is not available in Australia) and several new links with overseas soils and agricultural researchers were established. The following report outlines the experiments that were performed and briefly discusses some of the outcomes from this research. Further analysis of data from these experiment is taking place at CSIRO Division of Soils

From this visit I gained: 1. A good overview of the state of agricultural soil mechanics worldwide. I was struck by the lack of direction and novelty in some of the work in this field. I am convinced that the work pursued in Canberra for the CRDC is amongst the best being undertaken anywhere in the world. 2. An appreciation of the shift in emphasis in research in agricultural soil mechanics, which in some respects mirrors the situation in the cotton research ~ the problems of tillage and compaction have been well studied, and are now of lower priority. Some environmental issues are rising in importance.and much soil mechanics research is now turning in these directions. 3. A detailed appreciation of many particular pieces of research, both through the conference papers and through the visits to research centres. There were a number of papers on compaction and stress measurement at the conference. I presented a paper on the uncertainty in compaction predictions that arises from the variability of soil properties. At the various research centres I saw work on permanent beds, agricultural soil mechanics following my own work, the mechanics of root growth, tillage and soil structural problems. I also discussed the experimental design and progress of work by Bruce Blunden undertaken under project CS06C, and reviewed some of the early results.

Aim of Travel: To participate in the Vlth International Co11oquium on Invertebrate Pathology and Microbial Control. The Colloquium also incorporated the Second International Conference on Bacillus thuringiensis