Narrow row cotton (rows spaced less than 40cm apart) has long been seen as a potential alternative system for Australian cotton, especially in regions with shorter growing seasons. The aim of these systems has been to reduce harvest costs and achieve earlier maturity without sacrificing yield. Advances in technology and positive commercial experience in shorter season production systems where Pix®, Bollgard II and Roundup Ready technologies are available has renewed interest in narrow row production across the industry. In certain regions with particular management strategies alternative row configurations may offer significant opportunities. Further interest has been generated by recent advances in harvesting technology from John Deere that allow spindle picking of narrow row cotton crops (38cm rows), with claims of improved yield and earlier maturity while avoiding the risk of discounts for fibre quality associated with harvest.

Detailed studies to improve our understanding of differences in the growth and development of cotton in conventionally spaced (1m) and ultra-narrow row (UNR – 25cm row spacing) production systems were conducted as part of postgraduate studies by Rose Roche. Despite this research, there continued to be limited understanding of cotton’s growth response to different row configurations (especially 38cm row spacing) in the warmer high-input Australian environments. Conceptually, in high-input systems, the high density planting of narrow row systems reduces the time to crop maturity, as fewer bolls per plant need to be produced to achieve yields comparable to conventionally spaced cotton crops. In practice, again this earliness has been difficult to achieve consistently in UNR trials in both Australia and the US despite the level of crop inputs.

This project aimed to enhance our understanding the interaction between crop yield and maturity with plant population (row configuration x within-row spacing) so that opportunities to achieve earlier maturity or higher yields can be exploited, and management strategies to allow this developed. This will fill a significant gap in our current knowledge of crop agronomy and management. During the course of the project a total of 13 field experiments were conducted that investigated: growth of cotton in different row configurations; growth of cotton grown in different row configurations and populations; Bollgard II vs. conventional (non-Bollgard II) in different plant populations; and agronomy of narrow row systems.

In summary the outcomes of this project that were tangible and tested included the following:

• Plant population differences from both changes in inter and intra row spacing had little or no consistent response on yield, quality or maturity. Narrow row systems (38cm) did not improve yield or cause earlier maturity.

• The addition of earlier and higher inputs of water and nitrogen did not overcome plant competition effects leading to improvements in yield in 38cm row spacings.

• No differences in management were identified between 1m and 38cm row spacings. Pix management was not different, re-confirming results of Rose Roche’s thesis.

• No differences were identified in the response of non-Bollgard II and Bollgard II varieties to changes in plant population (including row spacing).

• Uniform plant population is vital for achieving optimum yield.

Importantly the researcher working with growers on experiments undertaken in this project was able to identify a number of intangibles outcomes. Therefore crop management recommendations resulting from this work therefore include:

• There are no clear benefits of 38cm narrow row cotton systems for improving yield, quality and earlier maturity in Australian high input cotton systems on the majority of soil types on which cotton is grown.

• Management considerations for narrow row systems are not different to 1m row spacing.

• Intangible issues need to be evaluated when considering a change to narrow row production systems.

• No changes in management are needed for high fruit retention Bollgard II with changes in plant population.

• Uniform plant establishment is critical to maximise yield.