Jon Baird was appointed in the role of the lead researcher CottonInfo Tech Lead – nutrition.

During the project, Jon developed new research extension materials and collaborations within

the cotton industry to further improve grower’s knowledge and nutrition management

practices. Within the project there was a major revision to the annually produced Australian

Cotton Production Manual – nutrition chapter. The ACPM is a cornerstone for the industry and

delivers a standard for best management practices for Australian cotton growers and industry

personnel. The revision was based on recent data detailing N fertiliser losses in field tailwater

and quantification of N fertiliser movement within the soil profile. In addition, the project

developed specific nutrition management guidelines outlined for dryland cotton systems. The

guidelines gave growers a detailed management strategy similar to what is available for

growers using irrigation water.

As reported in other documents and reports many Australian cotton growers are applying

fertiliser N higher than what is required by the planted crop (industry fNUE was ~10 kg lint/kg

N compared to research optimum range of 13-15 kg lint/kg N). Therefore, a concise effort

was made to better understand the tools and strategies growers and agronomists use to

perform nutrition budgets. Through organised regional face-to-face surveys and nutrition

forums the project evaluated the industry’s thoughts on nutrition management and key goals

and processes which can reduce fertiliser loss and the production of gaseous emissions and

reduce the industry carbon footprint.

Survey results indicate 89% of growers use a nutrient budgeting tool, but the tool was not

the traditional industry developed tool – NutritLogic – but rather individual excel sheet

containing known formulas and factors. Also, growers were willing to utilise enhanced efficient

fertilisers (EEF) and were in favour of fertilisers that have a potential for lower carbon

emissions.

To generate greater industry knowledge and understating of nutrition, the project established

on-farm experiments to investigate N mineralisation utilising the CSD FastStart weather

stations network and an EEF study in the Southern valley. Mineral N dynamics across all the

Australian cotton valleys were monitored throughout the growing season. Research results

indicated application timing affected available mineral N, with pre-plant timing losing mineral

N from the 1st irrigation down to maturity, while in-crop application gave crops a spike of

mineral N during the mid-season months of December/January.

During the project, there was a noticeable drop in the application rate of fertiliser N from

2017/18 to 2020/21 (336 kg N/ha and 253 kg N/ha respectively). The decrease in application

rate had a positive influence on irrigated cotton fNUE (14 kg lint/kg N) which was the first

recorded industry fNUE in the optimum range of 13-18 kg lint/kg N in the last ten years of

CRDC grower survey data. While factors such as smaller production area and higher mineral

N from fields in long fallows may have contributed to the fall in application rate, there has

been a conscious shift in grower attitude to improve their management on nutrition especially

as economic impacts such as low turnout and poor fibre quality are highlighting implications

of excessive N fertiliser use.

Verticillium wilt caused by the soilborne fungus Verticillium dahliae, is one of the most challenging and economically significant diseases of cotton in Australia and worldwide. Host resistance is regarded as the most effective control strategy, however the biological complexity of the pathogen and controversy regarding the mechanisms of resistance hinder plant breeding efforts. Previous studies have utilised GFP-tagged isolates of V. dahliae to investigate the host – pathogen interaction on cotton, providing insights into the host resistance response and little understood areas of the disease cycle. Here, we establish GFP-tagged isolate Vd71-3 as a tool for evaluating infection and colonization on cotton cultivars tolerant and susceptible to Verticillium wilt. Isolate Vd71-3 was obtained by transforming a GFP vector construct into highly virulent non-defoliating strain Vd71171 isolated from a diseased Upland cotton plant in NSW, Australia. Prior to study on cotton, pathogenicity of Vd71-3 was deemed consistent with that of the parent wildtype, indicating that GFP expression does not dramatically alter virulence. Confocal laser scanning microscopy observations confirmed existing descriptions of early infection on cotton, including germination of conidia by 24 hours post-inoculation, formation of an infection peg, intercellular colonisation of the root tips but not lateral root junctions, preferential colonisation of the xylem vessels, and acropetal movement of conidia in vessels. Extensive fungal occlusion of the vessels was also observed, not previously captured elsewhere on cotton.

V. dahliae was recovered from six of the eight weed species that were inoculated with the transformed VCG 1A and 2A strains. The VCG 2A transformant was recovered more frequently from weeds than the VCG 1A transformant, suggesting that V. dahliae VCG 2A may have higher infectivity towards weed hosts in Australian cotton fields. V. dahliae was not recovered from seeds from cotton plants that were subject to direct stem inoculation, although vascular tissue adjacent to the site of inoculation was colonised. Further investigation is needed to understand whether V. dahliae VCG 1A and 2A strains are capable of infecting Australian cotton seed using alternative inoculation techniques.

Host range of Verticillium dahliae and effect of rotations on overall soil health

Following pathogenicity testing in the glasshouse it was revealed numerous crop species were susceptible hosts to both defoliating and non-defoliating strains of Verticillium, which are the predominant strains causing wilt in Australian cotton.  These alternate host crops include mungbean, black gram, soybean, cowpea, lablab, pigeon pea, butterfly pea, chickpea, wheat, barley, oats, triticale and canary grass.  Like cotton there were differences in the severity of symptoms observed between the two strains of verticillium and between varieties of the one crop where multiple varieties were examined.  Varietal differences were observed in wheat, barley, chickpea, mungbean and lablab.  Crops that were proven to either aid in lowering inoculum levels or are non-hosts, based on field and glasshouse testing, include maize, sorghum, forage sorghum, Japanese millet, and white French millet.  Red panicum, Shirohie and Panorama millets were poor hosts under glasshouse conditions.  Symptomatic hosts supporting infection and being used as rotation crops potentially will aid in maintaining inoculum levels between cotton crops rather than providing a disease break.  Cereal residues, in particular wheat and barley, can support development of microsclerotia and V. dahliae is both seed-borne and transmissible in these crops.  This has potential implications in disease management and using cereals as a rotation crop in verticillium-infested cotton fields.  Both cereal residue and seed could act as reservoirs of further infection.  Despite infection of cereals not being observed under field conditions to date (possibly because of winter temperature), ground truthing being done currently for example by Crown Analytical, to determine inoculum loads before and after cereal and other crops will aid in a greater understanding of the potential risk these crops may pose in aiding inoculum carryover and/or disease spread.  Several plant species identified as hosts from this research should not be overlooked as possible bridging hosts for V. dahliae.

Change in the incidence and severity of cotton diseases

NSW

The annual cotton disease survey in NSW was first commenced in the 1983/84 season. The continuous surveillance program in NSW enabled us to monitor the disease prevalence, distribution and dynamics. Wilt diseases caused by Fusarium and Verticillium, and black root rot disease remained a major constraint for cotton production in NSW. With additional detection of a novel lethal wilt disease caused by a novel fungal Eutypella, the need for surveillance remains high. The disease was detected in many valleys in the past three seasons, except for Murrumbidgee and Lachlan. The disease survey program also allowed us for the first time to record a significant yield loss of up to 25% caused by Alternaria leaf spot in a dry land crop in NSW. Alternaria leaf spot has been long considered a minor disease, but this reaffirmed that under favourable conditions, a minor disease could result in a major loss. Similarly, a sporadic and under-studied boll rot also caused lots of yield loss concerns in the past three seasons due to wet weather conditions. 

Qld

At the completion of this project annual disease surveys in Queensland had been conducted consecutively for 20 years. Previously and within this project, the data collected has enabled an understanding of incidence, severity and distribution of those diseases present and insight was gained into emerging disease issues. Importantly, a new wilt disease named Reoccurring wilt was shown to be caused by two novel Eutypella species. The prevalence of this disease across regions was assessed by conducting annual disease surveys. The disease has been confirmed in Theodore, Emerald, St George, Darling Downs and the Border Rivers. In Queensland novel species 1 has been confirmed in Theodore, Moura, St George and Border Rivers, as well as Boggabilla and Mungindi in NSW. Novel species 2 has only been detected in Central Queensland. In Central Queensland, and particularly in the Dawson Callide, high reniform nematode pressure at planting has continued to impact seedling development. The presence of mungbean volunteers when planting back into cotton contributed to poor seedling growth since mungbean is a host of reniform. To date this nematode has not been detected in cotton fields outside of CQ. Fusarium wilt remains a key disease for the Darling Downs as well as fields in St George and Border Rivers region, with impacts felt early and late season due to highly conducive conditions. Verticillium wilt is prevalent in the Border Rivers, and the increase in incidence and impact continues to be of concern.  Areas on the Darling Downs were also significantly impacted by Verticillium wilt. Fields in the Border Rivers, St George and Darling Downs with both Fusarium and Verticillium wilt pathogens poses a significant management challenge. Environmental conditions are the key factors in determining infection rates of boll rots. In this study a low level of boll rots, in general, weas present, particularly when late-season rain was present. The most prevalent type of boll rot in Central Queensland was tight lock, whereas in the other regions of Queensland both boll rot and tight lock tended to occur. Leaf spots associated with several pathogens were detected on the Darling Downs and St George at a high incidence, and in some fields with high severity, occurring throughout the canopy as well as on young leaves. In some fields the complex of leaf spot pathogens was also associated with early senescence and significant leaf drop, hence there was grower concern of the potential impact of leaf spot diseases on yield. Fungi recovered from necrotic lesions included Alternaria alternata, Stemphylium lycopersici, Cercospora sp., Corynespora sp. and Pithomyces chartarum.  S. lycopersici and P. chartarum are not associated with leaf spot of cotton. Preliminary pathogenicity tests suggest that these fungi can initiate leaf spot on cotton leaves, however tests need to be replicated to confirm results. 

Soil microbial and biochemical elements that support and improve disease suppression potential of cotton soils

Surface soils from ongoing multi-year experiments and farmer fields from multiple cotton growing regions with different cropping histories and varying disease incidences were collected and analysed for the composition and abundance of microbial (bacteria and fungi) communities, microbial biomass, its catabolic potential and physico-chemical properties with an objective to determine the role of management practices on the disease suppression potential and overall soil biological health of cotton soils. 

Results from the multi-year field experiments indicate that (i) the inclusion of cover crops increased the catabolic potential, genetic diversity of soil fungal and bacterial community, total microbial biomass of cotton soils, (ii) cover crops and crop rotation with alternate crops caused a significant change in the composition of soil bacterial and fungal communities and (iii) fallow as part of crop rotation generally reduced microbial biomass and the diversity of microbial communities and abundance of soil fungal communities including plant pathogens. However, in spite of increases in microbial diversity not all cover crops, especially some crop mixes, improved suppression potential of soils to the soilborne fungal pathogen V. dahliae. Fungal communities in suppressive cotton soils were characterized by higher diversity and higher connectedness. Results on the high level of organization along with higher diversity in the soil fungal community in the suppressive soils developed due to long-term crop management or rotational crops such as Sorghum and Corn seem to provide the cotton plant with a stable microbial reservoir across varied seasonal environmental conditions. Overall, changes in microbial catabolic and genetic diversity would have contributed to the suppression of the pathogens such as V. dahliae, disease incidence and impact. Despite the observation of lower verticillium wilt pathogen levels after fallow would help in the reduction of disease incidence in the short-term, long-term adoption of such management practices would not benefit in maintaining or improving the overall soil biological health. This is especially important in cotton soils in Australia that seem to support microbial biomass levels that are below the threshold levels (i.e., MB levels <5% of soil organic carbon) and require regular C inputs to maintain biological functions essential for plant health and nutrition. The traditional continuous cotton system seems to promote the growth of pathogenic fungi such as V. dahliae and result in lower microbial diversity and abundances of beneficial microorganisms. Fallows can also cause a significant decline in the amount of soil microbial biomass (the ‘engine’ for all biological functions), microbial activity and genetic diversity of bacteria and fungi i.e., overall soil biological health, resulting in lower pathogen suppression capacity and weaken the biological buffer to reduce the impact of the soilborne diseases on cotton growth and productivity.

Results from the analysis of farmer field soils in this project clearly indicate the presence of a genetically diverse fungal community in cotton soils and distinct variation in the community composition and diversity between fields in different cotton regions confirming previous observations potentially requiring evaluation of management options across contrasting cotton growing regions.

The laboratory-based pathogen suppression potential assay developed for V. dahliae was further standardised and found suitable for soils from across different cotton regions. It provided a quantitative measure of a cotton soils ability to support or inhibit soil-borne fungal pathogens such as V. dahliae and found suitable to evaluate and identify different amendments that can potentially reduce pathogen growth. It presents a valuable tool to evaluate and/or identify potential management options to reduce pathogen growth as one of the measures to reduce disease incidence.

Eutypella – a new pathogen of cotton

This research characterised two novel Eutypella species recovered from diseased cotton and confirmed pathogenicity using Koch’s postulates. This is the first known report of a fungus from the Diatrypaceae family causing disease on cotton.  This new disease is referred to as Reoccurring wilt.

Bioassays using naturally infested field soil suggest that plant stress, such as that caused by drought, promotes infection and disease development. In addition, the disease was often first detected in areas of a field described as ‘poor’, due to soil constraints or other issues. Management that reduces plant stress and supports good growth such as well-formed beds, adequate and timely irrigations, and balanced nutrition, is recommended.

Four cotton cultivars evaluated for resistance to Eutypella under field conditions were all equally susceptible to the disease. However, multiple trials covering different regions to account for the different environmental conditions, pathogen diversity, and soil types, would need to be undertaken to fully understand varietal resistance to this pathogen before recommendations could be made.

It was observed in the field that root infection by the pathogen occurs and hypothesised that dead infected cotton trash is a potential source of inoculum. Removing dead wood from vineyards and tree crop plantations is known to reduce the likelihood of infection by pathogens belonging to the Diatrypaceae family, including Eutypella species. Hence management to reduce the quantity of cotton trash carrying over to the following season is proposed for the management of this disease. Crop rotation with non-hosts rather than back-to-back cotton is also recommended.

Roots from dead cotton plants exhibiting typical symptoms of Reoccurring wilt were analysed to determine their fungal community composition. The genus Eutypa represented by two Operational Taxonomic Unit of Eutypella scoparia were the most abundant fungi accounting for 45 to 99% of all sequences in the roots.  These results show that this pathogen can exclude other fungi from colonising the roots. Given this, the general microbial biological buffering may be weakened and could potentially increase infection by other opportunistic fungi. This raises the question, what impact might this have on the biology in field in the future crop if it is being reduced.

 

 

Although it has been several years since a major outbreak of silverleaf whitefly (SLW), the ongoing risk of honeydew contamination means they remain a pest of concern for growers in almost all cotton production valleys. Control of SLW still relies heavily on the use of insecticides, although biological control, including conserving natural populations and augmentation via parasitoid wasp releases, has been adopted by some growers.

Silverleaf whitefly resistance to pyriproxyfen emerged as a significant issue during the 2016/17 season. The industry responded by introducing a 30-day application ‘spray’ window to restrict pyriproxyfen use, aiming to reduce resistance selection pressure. From 2018 to 2020 this approach showed promise with a steady decline in the number of populations carrying resistance. However, in 2021 and 2022 close to half of the tested populations contained some resistant individuals. While the severity of resistance is lower than that observed in 2016/17, it is still a concerning reversal of the earlier trajectory.

Within the cotton industry, detection of SLW resistance to spirotetramat was first documented in Emerald in 2019. During the last three seasons, spirotetramat resistance was detected in populations collected from cotton in Emerald, Theodore, Darling Downs, Mungindi, and Macintyre and Namoi valleys. DNA sequencing of populations collected between 2019 and 2021 found the frequency of the mutation in resistant populations was low (1.2-4.1%). While current resistance levels are unlikely to cause management issues, SLW resistance to spirotetramat has the potential to increase (as already observed in other industries). A proactive change to the Insecticide resistance management strategy (IRMS) was made in 2019, reducing spirotetramat use to a single spray per field for SLW control.

A change in registration that occurred in 2020 now means buprofezin can be used in cotton for SLW control. Testing by bioassay has found no evidence of SLW resistance to buprofezin. Testing of laboratory strains with known resistance to pyriproxyfen and spirotetramat showed no signs of cross resistance to buprofezin. At the time of its inclusion in the IRMS, buprofezin was restricted to a single application when targeting SLW.

Widespread SLW resistance to imidacloprid and pymetrozine was found during testing in 2020. These results from 2020 and testing of laboratory neonicotinoid-resistant strain against a range of neonicotinoids show there is low-level cross resistance between imidacloprid and acetamiprid but no cross resistance to dinotefuran. Testing from 2020 to 2022 showed no definitive evidence of resistance to either acetamiprid or dinotefuran.

Resistance to the pyrethroid bifenthrin has been detected in many of the tested SLW populations over the past three years. This data, along with DNA sequencing data was recently published (Pest management Science, 78 – issue 8, August 2022,). Resistance to bifenthrin is widespread in cotton production regions, but within a population the mutation’s frequency is generally low (1-7%). In the same study, we documented that Bemisia tabaci Middle East-Asia Minor 1 (formerly B-biotype) is the dominant species found in cotton grown in NSW and QLD. The potentially invasive B. tabaci Mediterranean (formerly Q-biotype) was not detected in any of the samples.

Extension of project findings was circulated primarily via annual updates in the Australian cottongrower, via CottonInfo factsheets and by CottonInfo’s regional extension officers (REOs). Extension of SLW parasitism was achieved by engaging REOs in an in-field assessment of parasitism levels. The REOs gained firsthand experience and increased recognition of the value of biological control from parasitism during the exercise, which has been shared at a local level with agronomists.

Project Summary:

Purpose: To attend the Beltwide Cotton Conference to gain the latest knowledge on two key biosecurity risks to Australian cotton, guava root-knot nematode (GRKN) and areolate mildew (AM). To meet with Dr Bissonnette, Director of Agricultural Research at Cotton Incorporated and other pathologists to develop professional relationships and learn from international experts the management challenges of these new threats to Australian cotton.

What was achieved: Knowledge gained on the latest research conducted in the US on pathogens of concern to Australia and discussed opportunities with pathologists to learn from each other through collaboration.

The fungicide 'Revytek' showed promise for managing AM. Although results were variable across seasons, reduced incidence, increased yields, and economic benefit reported.

Given the limited fungicides available to manage this disease in Australian cotton and potential for the development of resistance to fungicides, a predictive model to determine when spraying is most likely needed to minimise loss is recommended. Potential to collaborate with Dr Allen.

Research undertaken in US to determine what races of GRKN are present, as all are not infective on cotton. GRKN is being monitored, but other plant parasitic nematodes such as reniform are of greater concern. To manage reniform nematodes, rotation sequences that include resistant cotton varieties and non-host crops, as well as a nematicide treatment are needed. Resistant cultivars are not yet available in Australia, and without these, it is extremely difficult to manage this pest. Farm hygiene and efforts to reduce spread to new fields and regions are crucial.

In the US, the fungus Xylaria necrophora is a pathogen of soybean and cotton is a new host. Cotton becomes diseased at the seedling stage and yields 1 – 14% less in seed cotton depending on seed treatment. Interestingly, this pathogen belongs in the same order of fungi as Eutypella, causing reoccurring wilt.

This 4 year project spanned a critical juncture as the CQ industry transitioned from Bollgard II® to Bollgard® 3 enabling more flexible growing arrangements. The local industry had been presented with the results of a 4 year study on the interaction between the local climate and cotton production with a key finding being that late-winter sowing may mitigate yield variability and stagnation. With a choice of planting very early or late this project benchmarked commercially-grown crops during the adoption period. An analysis of the growth of crops sown at different times would better inform decision making during a period of considerable change. Anticipating that pest management issues may again re-emerge in CQ with the increased 5 month sowing window, strategic sampling was also undertaken to re-assess Helicoverpa recruitment within the CQ farming system and compare it with a similar study conducted 20 years prior. The project also delivered national biosecurity leadership for the cotton industry within the CottonInfo program.
The project outcomes were
• Crop benchmarking confirmed that late-winter sowing best matched flowering and boll development with the summer solstice and a lower incidence of cloud or heat stress. An earlier harvest also reduced the risk of pre-harvest weathering, collectively enabling over 40% higher yields than traditional spring sowing without additional crop inputs. Traditional spring and later sowings coincided unfavourable climate with the more susceptible growth phases of late boll filling or early flowering respectively. Declining solar radiation and temperatures prevented yield recovery for the latest summer-sown crops.
• Growing crops on (second cycle flowering) is an effective tactic for overcoming pre-harvest weathering damage with the additional lint produced recovering lost yield whilst also diluting the contribution of damaged fibre and thus improving lint quality. Yield produced during the second cycle of flowering is akin to late December-sown crops (5-7 bales/ha). The combination of two boll cycles can enable very high final yield although crop periods well exceed 200 days.
• Double picked cotton produced very high yields (18-19 bales/ha). Sown in early August, the first crop is picked late January (11-12 bales/ha) and then ratooned and double picked in May (7 bales/ha) with base grade lint produced by both picks. Crop period exceeded 250 days.
• Helicoverpa recruitment in the farming system has changed markedly. Recruitment in chickpeas is a fraction of what it was (0-4900/ha) compared to 20 years ago (50,000-100,000/ha) with higher commodity price and new generation insecticides enabling judicious control. Bollgard cotton acts as a population sink with no meaningful recruitment. Pigeon pea refuges hosted the highest densities of pupae/m2 suggesting that these areas make a significant contribution from a RMP perspective. However, within the broader farming system the collective acreage is miniscule. The contribution of non-Bt exposed Helicoverpa from other crops (natural refugia) is much lower than historical studies would suggest.
• The awareness of farm biosecurity practices has risen amongst growers and industry through the delivery of biosecurity extension products and simultaneously the spread of endemic pests and diseases such as black root rot, Verticillium wilt and mealybug. The adoption of farm biosecurity practices has risen, with 44% of growers completing a farm biosecurity plan (identifying hazards and action plan). Going forward, it will be important to have external motivational drivers (e.g. rewards or incentives) to further increase the adoption of farm biosecurity plans by other growers in the Australian cotton industry.

This project provided strategic leadership for pest management and resistance stewardship across the cotton industry whilst also conducting research to better understand the relationship between early season fruit retention and the pursuit of very high yields. Key project outcomes were: 

• A successful campaign was conducted during the summer of 2019/20 to inform advisors and growers throughout the industry that drought conditions could significantly alter accepted silverleaf whitefly (SLW) management paradigms for honeydew lint contamination. This campaign involved various stakeholders (ginners, marketers & researchers) who collectively gave timely updates across the industry for locations spanning Griffith to Mungindi about the need for more stringent SLW management. Messages presented at these meetings were reinforced by newsletters, videos and online forums with the CCA to ensure the rapid dissemination of updated information for SLW management under dry conditions. Consequently, SLW were well managed across the industry with no reports of sticky cotton. 

• Numerous extension products (videos, newsletters and industry articles) and services (field walks, workshops, training and formal presentations) were created and provided to industry during this project. This extension was strategic with the purpose of encouraging longer term change for pest management practices across the industry as well as responsive to emerging issues (e.g. lint stickiness and locusts) each season. 

• A survey of Cotton Pest Management Guide (CPMG) users identified opportunities for content improvement. As a result, changes include a foldout chemical guideline, new images and re-written chapter sections. A range of resources that compliment the CPMG have been created including CottonInfo YouTube videos, an updated SLW management guideline and relevant responsive newsletters. 

The impacts of early season square loss on the growth, yield and quality of commercial irrigated Bollgard® 3 cotton was investigated at numerous locations spanning Emerald to Leeton. The ability of Bollgard® 3 varieties to compensate for early season square loss was high with no impact on yield and quality except for one research site (Leeton). Compensation occurred primarily through retention of bolls on more distal FB positions (>P2) immediately adjacent to lost positions. Consequently, crop maturity was minimally affected but the pattern of boll opening was altered (which may change defoliation commencement timing). For warmer regions north of Narrabri, the ability to rapidly compensate reinforces that square loss within the previously recommended range of 60-70% is inconsequential for yield potential, with experimental damage treatments far exceeding these levels without negative impact for yield, lint quality and final crop maturity. However, the results at Leeton and Whitton suggest caution is required for far southern sites and a need for additional replication across seasons and fields to better understand the circumstances and potential frequency under which suboptimal results arising from poor retention may occur. 

NOTE that this work is ongoing and therefore recommendations for industry practice for managing early season retention cannot be provided at this stage.

Cotton RDC commissioned this research to assist the cotton industry in understanding how it contributes to the Australian economy. The project has established a data framework and analysis that can be cost effectively updated and replicated over time. There are two main outputs of this project: — The value and importance of the cotton industry to the Australian economy. — An update to the results of the last study and comparison of the results between the 2021-22 and 2015-16 production years. The framework was built at the LGA level. The rationale for building the framework from an LGA level is that it provides more detail than a regional level, is better for statistical accuracy and Census data is reported at this level. Cotton is grown in 32 LGAs in Australia. Some of these LGAs produced very little cotton in 2016, and 14 LGAs (all located in NSW and Queensland) produced 88 per cent by volume in 2016. Unfortunately, 2021-22 production data was only available at the state level, not by LGA. 2020-21 was used as the base for breaking down state production into production by LGA, as it was the most recent year with production reported on by LGA. As the production seasons in 2015-16 and 2021-22 were very different, LGA production proportions in 2011-12, 2012-13, and 2016-17 (high production years) were applied to adjust this base to 2021-22 production levels. The same 14 LGAs were used as in the previous analysis. The data used in the analysis covered 99.5% of production in 2021-22. Note that ABS are changing the way they measure and report agricultural data, with LGA data expected to be reported on again in the future

Effective capture and storage of rain are major challenges for grain and cotton growers in the northern region where only 20-40% of rainfall is typically transpired by dryland crops, with 60% of rainfall lost to evaporation, and 5-20% lost in runoff and deep drainage. Recent research showed cover crops and increased stubble loads could reduce evaporation, increase infiltration and provide net gains in stored soil water over traditional fallow periods.

This project ran 13 experiments on low-cover fallows around Yanco, Parkes/Canowindra and Goondiwindi. The best cover crop treatments recovered the 40-60 mm water deficit taken to grow them by the end of the fallow in most experiments, which modelling suggests may happen ~70% of years at Goondiwindi. While some cover crops stored up to 38mm extra plant available water, others lost water in some very dry seasons. It seems that cover crops can protect the soil from erosion in low cover fallows and maintain stored water in a majority of years.

The amount of stubble required to achieve major reductions in erosion is relatively low and easily achieved. Cover crops that produced 1 t/ha dry matter were predicted to reduce long-term erosion by up to 82%, 2 t/ha by 96% and 3 t/ha by 99%. In dry years, the feed value of cover crops that were grazed easily exceeded the loss of grain yield from the water lost from the fallow. Interestingly, cotton and wheat yield increases were larger than expected from this stored water alone and deserve further investigation to understand the underlying causes and potential across the northern region.

The majority of the Australian cotton crop is harvested using the John Deere round-module harvester, which has led to an increase in the overall axle loads being applied to the soil, and a subsequent increase in the risk of soil compaction. The extent of any actual compaction will depend on soil characteristics, tillage history and prior soil structural condition, and especially the soil moisture content at the time of harvest. Soil compaction leads to several hidden issues for the cotton industry which can limit productivity and affect resource use efficiency. Once soil degradation occurs at depth in the soil profile root growth can be severely restricted affecting water and nutrient use and ultimately profitability. Sodicity is also a major constraint in many cotton subsoils. Subsoil sodicity leads to decreased rooting depth and is often exacerbated due to increased irrigation frequency in irrigated cotton. This project conducted in-field and laboratory studies to address soil compaction and cotton production; management of soil dispersion under sodic soil and irrigation water conditions; and development of improved analytic methods.