Experiments to establish the response of cotton plant to soil water stress under different soil types, climatic conditions and fruiting loads have shown that (i) the response of cotton to water stress is different on different soils (eg heavy clay vs. sandy-loam) (ii) these differences can be accounted for when soil moisture content is normalised for water holding capacity, expressed as the fraction of transpirable soil water (FTSW) (iii) that climate, especially evaporative demand, can cause plant stress even when the crop has adequate soil moisture and (iv) there is no difference in soil water extraction and therefore root development by crops with different levels of fruit retention.Field experiments were run over three cotton seasons at three sites with widely different soil types around Narrabri NSW. The response of the cotton plant to moisture stress, imposed by skipping irrigations around flowering, was measured as leaf water potential using a pressure chamber. Cotton plants were found to behave in the same way to moisture stress on all soil types when the soil water holding capacity of the soil was taken in to account and expressed as a percentage or fraction of transpirable soil water (FTSW). Over the three seasons prevailing climatic conditions have a large effect on the ability of the plant to cope with a given level of soil moisture deficit. Even under low levels of soil moisture deficit, on high evaporative demand days plants often experienced stress which had an impact on yield. There are some climatic conditions under which the cotton plant is unable to take up enough moisture even from a soil profile with readily available water that the plant will become stressed no matter if more water is applied. Identifying these conditions and their management implications are the subject of ongoing research.The results of this research will provide a basis for refined irrigation management through understanding the effect of climate and soil type to reduce water stress and providing decision points for future management. This information will also be included in decision support systems through inclusion in future versions of HydroLOGIC.A separate experiment conducted over two seasons also in Narrabri showed no difference in soil moisture extraction and therefore extent of root development between crops that have high and low levels of fruit retention before cutout. High retention crops (such as BG II®) should be irrigated in a similar manner to lower retention cotton. The high level of early reproductive development does not appear to affect the below ground vegetative development of the crop. A preliminary experiment was also conducted to investigate partial rootzone drying in cotton. This showed no benefit from partial rootzone drying in terms of cotton plant stomatal control, biomass production or yield.This project has significantly improved our understanding of basic responses of cotton to soil moisture stress and how this is influenced by climate and soil type. This knowledge is vital in developing improved irrigation strategies for cotton and achieving maximum yield from applied water.

The aim of this study was to use EM imaging and .a collected by a DUALEM-421 to infer the spatial distribution of soil properties and soil particle size fractions related to .a across a prior stream channel in an irrigated cotton field in the lower Gwydir valley. EM imaging is defined by Christensen (1997) as an approximate inverse mapping of data into a model.

This project is about the development and interpretation of a range of socioeconomic indicators for a sample of case study communities where the cotton industry is a significant industry. This is one of the reports from this project and relates to the economic indicators and their interpretation.

An essential component of the plant body is the root system. It provides anchorage and support for the plant to explore its substrate, to absorb water and nutrients and to transport them above ground to the shoot system. Root systems are highly adaptive and responsive to environment flux (Stokes et al, 1996, Annals of Botany 78: 415-421).The root systems in cotton may vary in different cultivars, for example, cultivars infected with different soil-borne pathogens and cultivars with varying levels of disease resistance may show different root characteristics. The soil-borne black root rot and fusarium (Fov) wilt pathogens have been used in this project to determine whether different disease resistant lines show variations in their root architecture. The root architectures between different genotypes grown under normal conditions are also assessed in this project. More robust roots in cotton cultivars are of great agronomic significance in its potential to protect against cotton diseases without the need for chemicals. Cultivars showing robust root characteristics may be incorporated into new lines.It was found that cotton root architecture varies with genotype. Additionally, cotton cultivars respond to exposure to the pathogen Thielaviopsis basicola with some cultivars showing an increase in root branching and others showing a decrease. Furthermore, degree of root branching was seen to vary with relative resistance to the fusarium wilt pathogen

The current project was devised in the knowledge that increased sodicity and salinity of percolating water will alter the saturated conductivity of many soils, especially sodic soils. Additionally, on commencement of the project the Cotton industry had minimal data or experimentation on the scale or driving forces behind deep drainage (DD) with furrow irrigation. The project had two principal objectives: to assess the effect of increasing salinity and sodicity of irrigation water on the DD under various cotton soil types, and to utilise drainage lysimeters to directly measure DD and correlate responses in column experiments to field response.

To obtain data for the first objective, a glasshouse experiment was conducted to assess the effect on DD of changes in salinity and sodicity levels, waters being applied to large intact cores collected from each field site. For the second objective, nine drainage lysineters were installed in 3 cotton fields (3 lysimeters over each field) and data collected over a period of two cotton seasons.

There were four major sets of results. Firstly, physico-chemical analysis of the soils (to 150 cm) at each site, showed the three sites to be quite different, particularly in their clay content being on average 75%, 55%, and 45% for the Dalby, Goondiwindi and St George sites, respectively.

Secondly, the quality of the irrigation water applied at each site was quite different, in terms of its salinity, with electrical conductivity of 3358, 498 and 137 (μS/cm) for Dalby, Goondiwindi and St George, respectively.

Thirdly, the drainage lysimeters (located at 115 to 150 cm below the soil surface collected water that is deemed “lost from the cotton root-zone”and hence is deep drainage. At the Goondiwindi and St George sites in both seasons (2002-3 and 2003-4) the ranking of the amount of DD at the three in-field locations was the same, with the head ditch receiving the most DD, then the mid and the least at the tail ditch end. Long-term inundation at the head ditch rationalises these results, whereas the tail end may remain dry if irrigation siphons are stopped early. In terms of quantities of DD, the Dalby site had the greatest recorded DD; 222 mm (= 2.2 ML of water) at the head ditch end in the first season but the other two sites also recorded several instances of >90 mm of DD in one season (0.9 ML) at the head and mid field locations.

Fourthly, in a glass house experiment, irrigation with high Electrical Conductivity (EC) and low Sodium Adsorption Ratio (SAR, a measure of sodicity) water increased drainage by 4, and 2 fold in Dalby and St George soils, respectively, compared with irrigating with fresh water; however, Goondiwindi did not show any change. Irrigation with low EC and high SAR water resulted in 2, 4, and 3 fold greater drainage in Dalby, St George, and Goondiwindi soils, respectively compared to fresh water. Irrigation with high EC and high SAR water showed 5, 3, and 1.3 fold drainage increase in Dalby, St George, and Goondiwindi soils, respectively compared to fresh water. These results demonstrate an interaction between soil type (probably clay content) and water quality on deep-drainage. Water lost to deep drainage was increased more by salinity than sodicity of the irrigation water in Dalby soil (high clay content), and more by the sodicity rather than salinity of the irrigation water in St George and Goondiwindi soils.

The relative timing of pest and beneficial arrival in the crops, and how the landscape context facilitates or hinders colonization processes is thought to be one of the key processes of lower pest populations. Early removal of pests avoids future damage, and often more importantly, it avoids future damage by the pests' offspring. Using crop scouting reports from the Border Rivers region of 4 fields with either low (<2%) or high (<20%) surrounding native vegetation, we evaluated for focal pests the: a) number of days to reach threshold, b) number of days above threshold, and c) number of above-threshold events. Our results show that pest population rarely reached threshold; only four species broke threshold for a total of 31 times in four years. We found no difference in the number of days to reach threshold between the two native vegetation treatments. However, there was a slight trend for aphids and Green Vegetable Bug (GVB) to spend more days over threshold in fields with low native vegetation (LNV) than in fields with high native vegetation (HNV). The opposite was true for plants infested with mites, which were above threshold for more days in fields with HNV. When considering all of the times that pest populations went above threshold, the LNV fields had an average 'broken-threshold' score twice as high as the HNV fields, and by comparison three organic cotton fields only broke threshold on average once a year. Further, when considering natural enemies, there was a significant but weak correlation between predatory beetles and aphids in HNV fields, but not in LNV fields.Ultimately this work was undertaken to evaluate the merit of simple measures to capture the value of native vegetation for the ecosystem services of pest control. Although additional study should be undertaken, the results have identified that there is scope to change crop scouting sheets for better capture of information to measure the value of native vegetation, and provide spray decision guidance. The new crop scouting report format could incorporate a section to track population trends of pests and beneficials over time, also allowing for easy accounting of the above measure. The results from this project suggest that these simple measures have merit when trying to link effects from native vegetation with the ecosystem services of pest control, but an investigation of more fields and regions is warranted.

Honours - Root growth, turnover and soil microbial biomass in Bt and non-Bt cotton (Gossypium hirsutum L.)

Cotton production in Central Queensland will continue to impose a unique set of challenges due to climate and it’s remoteness from other production areas. These challenges have been met successfully at an industry level in the duration of this project through strong collaboration between growers and local extension network.

Through the duration of the 5 year project, the cotton industry in Central Queensland has met and addressed some of it’s greatest ever challenges. The highlights of this include the successful development and utilisation of a management strategy for silverleaf whitefly, and the successful development and deployment of a strategy to prevent weed and disease movement into the region, and the establishment and nurturing of successful Area Wide Management Groups.

The project has been instrumental in developing a management program for one of the biggest insect threats, silverleaf whitefly. Without proper management, the destruction of fibre quality could permanently affect the marketability of Australia’s multi-million dollar cotton crop. The management strategy has been developed and adopted through strong collaboration between national and international research and development agencies and farmers and consultants. The template for management of this pest has been able to be transferred to other cotton growing areas in Australia.

The Central Highlands is one of the only cotton producing regions in Australia that has no confirmed cases of Fusarium wilt. The local industry took the proactive step of trying to maintain this status by developing a strategy to prevent the introduction of weeds and diseases into the region. This three-part plan involved 1) the compilation of a protocols document to be used by growers in implementing ‘on farm’ strategies, 2) establishing a facility for independent inspection of machinery entering the area, and 3) a wider community/ industry education program promoting the strategy including the installation of large road signs at the entrances to the district promoting the ‘Come Clean- Go Clean’ message. This program has had great success with excellent adoption and a continued ‘fusarium free’ status.

Central Queensland has been one of the pioneering regions for area wide management following the broad adoption of trap cropping in the late 1990s. Since that time, the momentum of area wide management has continued to grow to an extent where the groups operating in this region are amongst the most dynamic and successful in the industry. The involvement of the extension officer in this project has been paramount to maintaining the momentum of these groups. Outcomes of these groups have included the successful deployment of the management strategy for silverleaf whitefly, the ongoing high adoption of the IRMS and reduced incidences of odour complaints into town.

Whilst the successes of the Central Queensland cotton industry over the past 5 years have been principally been due to the fact that it has industry- wide involvement in all issues, the role of the extension officer in this process has been paramount.

Final Report Cotton yield and soil carbon under continuous cotton, cotton-corn and cotton-wheat

Final Report improving cotton yields on sodic soils - a new role for plant growth regulators Sodic soils present a major management constraint for large parts of Australia's cotton producing districts. A combination of structural, chemical and water constraints in these soils leads to reduced plant growth and yields (Yadav et al. 2011). One primary area of concern is the effect of sodicity in reducing the drought tolerance of cotton plants, particularly seedlings. Because much of the soil moisture stored in the top 10cm of soil is lost to evaporation, it is vital that seedlings can quickly access moisture at greater depths. Sodic soils compound this problem in multiple ways. The chemical environment reduces theosmotic potential, and thus the ability of the young plants to draw sufficient water. Also, the dispersive nature of these soils creates crusting and blocks macropores, reducing infiltration and overall water supply under rain-fed conditions (Ghosh et al. 2010). Along with these factors, sodic soils, particularly Vertosols, can demonstrate high soil strength which makes it difficult for seedling roots to penetrate the soil (Odeh and Onus 2008). Cotton plants arewell adapted to water stress and the chemical environment of sodic soils (Dodd et al. 2010). Most growth constraints, therefore, are likely to be attributable to structural limitations in physically preventing root access to water.Mepiquat chloride is a synthetic plant growth regulator widely used in cotton production to maintain a regular crop and prevent excessive vegetative growth under high temperature conditions (Yeates, Constable and McCumstie 2005). It reportedly interacts with natural plant hormones, increasing the levels of auxin and cytokinin hormones in the middle region of the primary root (Duan et al. 2007), and suppressing gibberellin biosynthesis (Yeates, Constable and McCumstie 2005). The suppression of gibberellin production is believed to slow internode lengthening by limiting cell enlargement (Reddy, Reddy and Hodges 1996), which is the agronomic effect intended. Duan et al. (2007) found that mepiquat chloride also increased lateral root primordia development and lateral root growth, apparently in connection with the increased levels of auxins and cytokinins. Other reports have also found increases in root growth from treatment with mepiquat chloride (Xu and Taylor 1992; Iqbal et al. 2005), which can have beneficial effects in terms of drought tolerance, particularly forseedlings (Xu and Taylor 1992).