Strengthening the Central Highlands cotton production system

Abstract

Central Queensland is geographically and climatically distinct from Australia’s other cotton production regions and as such presents both opportunities and challenges for cotton production and the farming system. This project examined the Emerald climate to identify opportunities that might enable the production of more consistent cotton yields and quality in what can be a highly variable climate. The climatic analysis identified that spring and early summer is the most optimal period for boll growth and maturation. However, to unlock this potential requires unseasonal winter sowing that is 4 to 6 weeks earlier than the traditional mid-September planting time. Consequently our research investigated: (i) how much earlier can cotton be sown whilst maintaining reliable crop establishment, (ii) what benefits could accrue with earlier sowing both in terms of yield and quality and (iii) how should agronomic management be varied to optimise crop performance when sown early. Data collected over 4 years has demonstrated that August sowing offers the potential to grow reliably higher yields compared to the traditional spring planting window with an average improvement of 2.2 b/ha per annum (23%) with no additional outlay except extra seed costs at planting. Earlier sown crops have proven to be easier to manage, as boll setting is confined to more favourable spring and early summer conditions. A measured benefit has been an average saving of 0.9 ML/ha pa over three years for the irrigation water required. The other surprising outcome from this research has been the reliably poorer yields achieved from the mid-September sown cotton treatments over four years. Every season the yield potential of September sown cotton was compromised by deleterious weather conditions (e.g. cloud, heat waves or rainfall) highlighting the inherent limitations that have been associated with the traditional Bollgard II® mid-September to late October planting window. August sowing does not negate the risk of wet weather at picking but compared to the traditional mid-September to late October sowing window the level of crop exposure is significantly reduced and the increased yield potential offers a sizable buffer against lint quality downgrades if they occur. This research has been conducted in partnership with growers and consultants at a commercial scale without forsaking scientific rigour. The experiments were also fully utilised for extension purposes so that growers could experience research results in real time. The outcome has been rapid adoption of August sowing by CQ growers with 70% of the Central Highlands crop planted in August for the 2017/18 season just months after the completion of this research project. The project also examined the pest status of symphylids a soil dwelling organism that had been considered to cause crop establishment problems in some seasons in CQ. Survey data suggests that this organism alone is an unlikely causal agent for crop establishment problems with damaged fields found to have a complex of other contributing soil pests and pathogens present. Experiments to better understand boll rots were also conducted during the project. This research suggests that some of the causal pathogens for tight locking may gain entry to the boll during the pollination process although the development of disease is still dependent on favourable (wet) conditions during flowering and boll opening. A wide array of pathogens were identified from tight locked bolls with the abundant presence of Alternaria spp. suggesting that this group of pathogens (typically associated with leaf disease) might also be significant in the incidence of tight lock disease in CQ.