Environment and cotton fibre quality

Along with historical climate data, the daily outputs of Commonwealth Scientific and Industrial Research Organisation (CSIRO) Conformal Cubic Atmospheric Model driven by four general circulation models (GCMs) were used by a stochastic weather generator, LARS-WG, to construct local climate scenarios at nine key cotton production areas in eastern Australia. These local climate scenarios were then used by established crop-level empirical relationships that firstly estimated the time and average temperature when the majority of cotton bolls in a crop are thickening their fibres, and secondly related this estimate of temperature to fibre micronaire. Micronaire is an indirect measure of fibre fineness and maturity. It is an important attribute of cotton fibre quality influencing spinning and dying processes. A significant change in micronaire occurs when it changes by 0.1 of a unit, which can move it into, or out of the optimum range of 3.8–4.5. Monthly mean rainfall and average wet spells for autumn months (i.e. March, April and May) were also analysed to examine their potential impact on cotton fibre grade (e.g. colour). Included in the micronaire impact assessment, we considered four planting times: normal planting, 15 days earlier and later than normal planting, and 30 days later than normal planting. Research data showed that when compared to the baseline (current climate and normal planting) (1) climate change with normal planting increased mean micronaire 0.04 ~ 0.33 in 2030 across all locations with Hillston increasing the most (from 4.06 to 4.39) and St George and Bourke with negligible increases (from 4.56 to 4.60, from 4.60 to 4.64, respectively) and decreased the chances of attaining optimum micronaire (3.8–4.5) in 2030 at most of the locations; (2) earlier planting (15 days) increased mean micronaire (0.03–0.34) across locations with Hillston increasing the most (from 4.06 to 4.40) and St George with negligible increase (4.56–4.59) and decreased the chances for micronaire falling in the optimum range at most of the locations; and (3) later 15 and 30 days plantings also increased the mean micronaire at all locations with the increase of ≥0.1 at three locations, and decreased the chances for optimum micronaire at most of study locations (7–100 % and 1–100 % for 15 and 30 days late planting respectively). However, there was an improvement in the frequency of obtaining optimal micronaire at five locations due to late plantings compared with early planting even though they could not offset the negative impacts of increased temperature on micronaire in comparison with baseline. This suggests that other management options such as plant breeding need to be put in place to counteract the impact of increased temperature on micronaire. Increases in monthly mean rainfall and the average length of wet spells in autumn were found indicating negative impacts on fibre quality with greater risk found at Hillston and Narrabri, followed by Goondiwindi and then the others. However, when the risks of rainfall were investigated on a monthly basis, there was reduced probability of increased rainfall and wet spells associated with May. This may assist with crops potentially grown for longer under the warmer conditions in Australia. This study provides useful information for the cotton industry to adapt to a changing climate from the perspective of developing strategies that may assist in maintaining cotton fibre quality.