Rose Roche and Michael Bange. CSIRO Plant Industry, 21888 Kamilaroi Hwy, Narrabri, 2390, Australia
Ultra-narrow row cotton (UNR - rows spaced less than 40 cm apart) has long been seen as a potential alternative system to 100 cm row systems. In Australia, the perceived benefits include improved yield and earlier crop maturity, which are especially beneficial in shorter growing season areas. In addition, recent advances in harvesting technology allowing spindle picking of cotton crops grown with 38 cm row spacings, may increase the benefits of these systems by avoiding the risk of trash discounts for fibre quality normally associated with stripper harvesters. Recent research in Australia with high-input cotton crops grown with 25 cm row spacings have not shown maturity or yield benefits. Studies were initiated to investigate whether differences in fruit retention offered by transgenic Bollgard II® cultivars affected the yield and maturity of cotton when grown at different row spacings. In 2004/05, we compared the yield and maturity of Bollgard II and non-Bollgard II cotton cultivars in four different row spacings (25 cm, 38 cm, 100 cm and 200 cm) with different plant populations. Neither lint yield nor maturity was significantly affected by UNR row spacing. Importantly, the Bollgard II cultivar had the same responses to row spacings as the non-Bollgard II cultivar. Despite the Bollgard II cultivar having earlier maturity than the non-Bollgard II cultivar there was no difference in yield. Yield components were affected: boll number increased as row spacing decreased, but boll size was smaller. The non-Bollgard II cultivar had higher boll number, but had smaller boll size. Fiber quality parameters were largely unaffected by cultivar or row spacing, although fiber length was longest in the 200 cm spaced crop suggesting less water stress at flowering, and the Bollgard II cultivar had longer but slightly weaker fiber than the conventional cultivar. The benefits of UNR systems compared with conventional spacing consequently remain uncertain and 38 cm rows responded similarly to 25 cm rows. Careful manipulation of crop growth through nutrition, irrigation and growth regulators may help realise benefits of UNR systems.
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