Robert J. Farquharson

A survey of management and economic impact of weeds in dryland cotton cropping systems of subtropical Australia

In dryland cotton cropping systems, the main weeds and effectiveness of management practices were identified, and the economic impact of weeds was estimated using information collected in a postal and a field survey of Southern Queensland and northern New South Wales. Forty-eight completed questionnaires were returned, and 32 paddocks were monitored in early and late summer for weed species and density. The main problem weeds were bladder ketmia (Hibiscus trionum), common sowthistle (Sonchus oleraceus), barnyard grasses (Echinochloa spp.), liverseed grass (Urochloa panicoides) and black bindweed (Fallopia convolvulus), but the relative importance of these differed with crops, fallows and crop rotations. The weed flora was diverse with 54 genera identified in the field survey. Control of weed growth in rotational crops and fallows depended largely on herbicides, particularly glyphosate in fallow and atrazine in sorghum, although effective control was not consistently achieved. Weed control in dryland cotton involved numerous combinations of selective herbicides, several non-selective herbicides, inter-row cultivation and some manual chipping. Despite this, residual weeds were found at 38–59% of initial densities in about 3-quarters of the survey paddocks. The on-farm financial costs of weeds ranged from

Diagnosis, extent, impacts, and management of subsoil constraints in the northern grains cropping region of Australia

148 to 224/ha.year depending on the rotation, resulting in an estimated annual economic cost of

Should we manage soil organic carbon in Vertosols in the northern grains region of Australia

19.6 million. The approach of managing weed populations across the whole cropping system needs wider adoption to reduce the weed pressure in dryland cotton and the economic impact of weeds in the long term. Strategies that optimise herbicide performance and minimise return of weed seed to the soil are needed. Data from the surveys provide direction for research to improve weed management in this cropping system. The economic framework provides a valuable measure of evaluating likely future returns from technologies or weed management improvements.

An Economic Framework for Sharing Water Within a River Catchment

Productivity of grain crops grown under dryland conditions in north-eastern Australia depends on efficient use of rainfall and available soil moisture accumulated in the period preceding sowing. However, adverse subsoil conditions including high salinity, sodicity, nutrient imbalances, acidity, alkalinity, and high concentrations of chloride (Cl) and sodium (Na) in many soils of the region restrict ability of crop roots to access this stored water and nutrients. Planning for sustainable cropping systems requires identification of the most limiting constraint and understanding its interaction with other biophysical factors. We found that the primary effect of complex and variable combinations of subsoil constraints was to increase the crop lower limit (CLL), thereby reducing plant available water. Among chemical subsoil constraints, subsoil Cl concentration was a more effective indicator of reduced water extraction and reduced grain yields than either salinity or sodicity (ESP). Yield penalty due to high subsoil Cl was seasonally variable, with more in-crop rainfall (ICR) resulting in less negative impact. A conceptual model to determine realistic yield potential in the presence of subsoil Cl was developed from a significant positive linear relationship between CLL and subsoil Cl: Since grid sampling of soil to identify distribution of subsoil Cl, both spatially across landscape and within soil profile, is time-consuming and expensive, we found that electromagnetic induction, coupled with yield mapping and remote sensing of vegetation offers potential to rapidly identify possible subsoil Cl at paddock or farm scale. Plant species and cultivars were evaluated for their adaptations to subsoil Cl. Among winter crops, barley and triticale, followed by bread wheat, were more tolerant of high subsoil Cl concentrations than durum wheat. Chickpea and field pea showed a large decrease in yield with increasing subsoil Cl concentrations and were most sensitive of the crops tested. Cultivars of different winter crops showed minor differences in sensitivity to increasing subsoil Cl concentrations. Water extraction potential of oilseed crops was less affected than cereals with increasing levels of subsoil Cl concentrations. Among summer crops, water extraction potential of millet, mungbean, and sesame appears to be more sensitive to subsoil Cl than that of sorghum and maize; however, the differences were significant only to 0.7 m. Among pasture legumes, lucerne was more tolerant to high subsoil Cl concentrations than the others studied. Surface applied gypsum significantly improved wheat grain yield on soils with ESP >6 in surface soil (0–0.10 m). Subsurface applied gypsum at 0.20–0.30 m depth did not affect grain yield in the first year of application; however, there was a significant increase in grain yield in following years. Better subsoil P and Zn partially alleviated negative impact of high subsoil Cl. Potential savings from improved N fertilisation decisions for paddocks with high subsoil Cl are estimated at ~

Improved beef production from supplementation of Hereford, Brahman and crossbred cattle grazing low and medium quality pastures in the subtropics of Australia

AU10 million per annum.

The Economics and Perspectives of Site Specific Irrigation Management in Australia

Two issues prompted this paper. The first was the measured soil organic carbon decline in fertile northern Australian soils under continual cropping using traditional management practices. We wanted to see whether it was theoretically possible to maintain or improve soil organic carbon concentrations with modern management recommendations. The second was the debate about use of sustainability indicators for on-farm management, so we looked at soil organic carbon as a potential indicator of soil health and investigated whether it was useful in making on-farm crop decisions. The analytical results indicated first that theoretically the observed decline in soil organic carbon concentrations in some northern cracking clay soils can be halted and reversed under continuous cropping sequences by using best practice management. Second, the results and associated discussion give some support to the use of soil organic carbon as a sustainability indicator for soil health. There was a consistent correlation between crop input decisions (fertilisation, stubble management, tillage), outputs (yield and profits) and outcomes (change in soil organic carbon content) in the short and longer term. And this relationship depended to some extent on whether the existing soil organic carbon status was low, medium or high. A stock dynamics relationship is one where the change in a stock (such as soil organic carbon) through time is related not only to the management decisions made and other random influences (such as climatic effects), but also to the concentration or level of the stock itself in a previous time period. Against such a requirement, soil organic carbon was found to be a reasonable measure. However, the inaccuracy in measuring soil organic carbon in the paddock mitigates the potential benefit shown in this analysis of using soil organic carbon as a sustainability indicator. These results are based on a simulation model (APSIM) calibrated for a cracking clay (Vertosol) soil typical of much of the intensively-cropped slopes and plains region of northern New South Wales and southern Queensland, and need to be interpreted in this light. There are large areas of such soils in north-western New South Wales; however, many of these experience lower rainfalls and plant-available soil water capacities than in this case, and the importance of these characteristics must also be considered.

Climate change impacts on phenology and yields of five broadacre crops at four climatologically distinct locations in Australia

A framework for sharing a limited quantity, but also a variable quantity, of water between irrigation and the environment to maximize social wellbeing is developed and illustrated. The optimal water allocation equates the marginal social value of water across different uses. A simplified illustration allocates water from the Goulburn River in northern Victoria, Australia, between environmental water to increase numbers of Golden Perch (GP) fish stocks and irrigation demand for water for dairy farmers. The value of water for GP is developed using a combination of fish numbers as an ecological response function of water and Choice Model estimates of willingness to pay by Victorian households for improved fish stocks. Irrigation demand for water by dairy farmers is developed using a Linear Programming study. The complex ecological response functions require a numerical search model to evaluate the socially efficient allocation of water between the different uses. The shadow price of water as optimally allocated between the environmental and agricultural uses is developed as seasonal water availability varies. Further development of the framework could include identifying dependencies within the ecological responses and incorporating multiple ecological and agricultural responses in an expanded model. The policy implications include information on the socially efficient allocation of limited water between irrigation and the environment and the value of water when shared optimally between uses.

Farming Systems in the Northern Cropping Region of NSW: An Economic Analysis

Subtropical grasslands are low in organic matter digestibility (OMD) (0.60) and nitrogen (N) (15 g/kg) for much of the year and this limits cattle production which is characterized by low calving rates and low weaning weights. Production has been based on Bos taurus British breeds of cattle but this is changing and now many breeding herds comprise B, indicus cows and their crosses. This change has increased some aspects of production, but low calving rates persist. A 4-year study was undertaken with a view to improve calving rates and weaner output by supplementing cows grazing either native or improved pastures with a high protein oilseed meal (cottonseed meal; CSM) on four sites. These sites were subdivided into a total of 36 paddocks to allow for two replications in a 3 breeds X 3 supplementation rates X 2 pastures factorial design. Selected cows (no. = 216) from Hereford (H), Brahman (B) and Brahman X Hereford (BH) breed types were set to graze either native pastures (0.45 to 0.62 OMD, 8 to 15 g N per kg; low quality) or improved pastures (0.47 to 0.67 OA ID, 10 to 22 g N per kg; medium quality). Cows were given either 0, 750 or 1500 g/day of CSM for 130 days from calving until 4 weeks into a 12- to 13-week mating period. The CSM was given as two meals per week. Live weight at mating of cows on the low quality pasture was increased (P < 0.01) over those not supplemented by feeding either 750 g CSM per day (H and B cows) or 1500 g CSM per day tall cows). There was no significant effect of supplementation on the mating weights of B cows grazing the medium quality sites. Calving rate of B cows was not increased by their supplementation on either low (4-year mean 58.3 %) or medium quality pastures (66.8%) but did tend to be higher in H cows when supplemented at 1500 g CSM per day on the low (66.7 v. 78.0 (s.e. 6.09) %; P < 0.1) and medium quality pastures (70.5 v. 93.5 (s.e. 4.72) %). An increased calving rate (65.8 (s.e. 6.6) % to 83.2 (s.e. 5.82) % in supplemented BH cows grazing low quality pastures approached significance (P < 0.1) when given CSM at 1500 g/day but there was no increased trend in calving rate when this breed type was supplemented on medium quality pastures. Weaning weights of calves from and B and BH cows were increased (P < 0.05) by supplementation of their darns at 750 g/day and for calves weaned from H cows supplemented at 1500 g/day of CSM. Supplementation at 1500 g/day on low quality pastures increased weaner output per cow mated by 120% for H, by 65% for BH cows and by 50% for B cows. Weaner output was increased by 34 and 40%, respectively, for B and H cows when supplemented at 750 g/day and grazing medium quality pastures but there teas no significant effect of supplementation on output from BH cows. Responses in many parameters differed between years. These results were interpreted as a response to the protein in the oilseed meal supplement by B, taurus and B. taurus X B. indicus cross cows grazing on the subtropical pastures. The study also highlighted that responses to the meal differed between breed types, between the quality of the grazed pasture and between the years of supplementation.

Economic analysis of improved perennial pasture systems

Automated furrow irrigation is a new technology being developed commercially and offered to farmers in Australia. Improvements in water, fertiliser and labour efficiencies are possible with the more precise management of irrigation water, albeit with initial capital and ongoing management costs. The systematic quantification of potential benefits is a strength of the analysis reported here, which provides information for cotton growers in the Namoi Valley of northern New South Wales (NSW), Australia. Further, an economic investment analysis which considers the benefits and costs over a 20-year period shows potentially favourable returns on investment in this technology.