Planting time and associated temperature factors affecting cotton production on the southern Darling Downs, Queensland

Abstract

In a trial at the Hermitage Res. Stn, Ceresan-treated or untreated cotton seed was sown on 18 and 26 Sept., 9, 25 and 30 Oct. and on 11 Nov. Weather conditions were unfavourable to germination following the 21 Oct. and 9 Nov. sowings. Total emergence (mean of untreated and treated seed) was significantly higher for the 9 and 30 Oct. sowings (59.58 and 64.17%, respectively) than for the 18 and 26 Sept. sowings (49.55 and 42.85%). Time to maximum emergence varied from 25 days in Sept.-sown to 12 days in Nov.-sown cotton. Seedling emergence was higher with Ceresan-treated seed for all sowing dates. Rate of emergence was slower in early sowings. Early-sown cotton showed slow initial growth; that sown on 18 Sept. took 140 days from sowing to peak flowering, compared with 98 days for cotton sown on 18 Nov. There was little seedling mortality due to low air temperature. Insect injury to seedling apices was more prevalent (89% damaged apices) in Sept.-sown than in Nov.-sown cotton (21%). Boll opening was slow because of the cool, humid autumn conditions. With the marked decline of the summer season, cotton bolls in the top-crop formation were generally undersized and contained a high proportion of immature cotton. Sept.-sown cotton produced the highest total yields of 2000 Ib/ac and sowings up to 9 Oct. matured considerably earlier than later sowings. While Sept.-sown cotton produced the highest yields in this trial, seasonal conditions were relatively mild, and sowing in early Oct. is recommended to avoid risk of prolonged exposure to low temperatures which reduce seed germination and retard early plant growth.-F.A.S.