Soil temperature and soil water potential under thin oxodegradable plastic film impact on cotton crop establishment and yield

Field experiments were undertaken to determine the effect of oxodegradable thin film on cotton establishment and lint yield. It was hypothesised that the use of thin oxodegradable plastic film would increase soil temperature and conserve seedbed water possibly reducing the risk in early planting, while not reducing lint yield or fibre quality of cotton. Experiments were conducted near Narrabri, NSW Australia during the 2010, 2012-2014 and the 2012 and 2013 seasons near Griffith, a cooler region in southern NSW with three or four thin oxodegradable plastic films with different formulations and break down rates being compared with a bare soil treatment. Planting depth soil temperature and soil water potential was monitored at three hourly intervals. Soil temperatures were elevated by 2-4 degrees C under the film compared with the bare soil that resulted in earlier (2-4 days) emergence of cotton under the film compared with bare soil. Soil also remained wetter beneath the film. Two films began to degrade at the time when cotton seedlings emerged (10-20 days), resulting in greater seedling survival (2-7 vs 12 plants/m). Seedlings were unable to penetrate four films on emergence and did not survive. When these films were slit to allow seedling growth, survival depended on subsequent environmental conditions; whether overcast/sunny or cool/warm conditions occurred. Using film that had been slotted prior to being laid in the field also increased soil temperature and conserved seedbed water. This enhanced (50-80%) emergence and survival of emerged seedlings, and overcame the need to slit film in the field. A climate analysis and simulation study was also conducted to determine the benefit or otherwise of thin film and early planting over a longer-term than is possible from field studies. Results for both sites indicated that the earlier the planting date (August/September), compared to a "normal" planting date (October) there was a greater the chance of cold (6.5 vs 2.5 days) and frost (2.5 vs 0 days) being experienced, which resulted in lower or no lint yield. Lint yield tended to be greater (3200 vs 2800 kg lint/ha), although not significantly so, with thin film compared with bare soil. Fibre quality parameters were not affected by the use of thin film. All surface film had degraded by the end of the season posing no risk of contamination of the lint. Film below ground did remained intact, but this does not pose a contamination risk for the cotton lint at harvest. No plastic film was detected in ginned cotton after being machine harvested at both sites. There was no significant benefit in lint yield due to thin film, while all fibre quality parameters made base grade. Long-term simulation of early planting, with and without thin film, indicated that lint yield was variable with no consistent benefit due to the presence of thin film for the locations simulated. There is still a risk of cold weather or frost occurring when planting early with thin film that growers need to consider. In practical terms it is anticipated that growers would potentially only plant 5% of their area early depending on the seasonal forecast. Crown Copyright (C) 2015 Published by Elsevier B.V. All rights reserved.