Growers whose water supply is critically low and are experimenting with novel ways to grow cotton with this limited water. These include irrigated skip-row techniques which are showing promise following a number of successful crops in recent seasons. However

no recent studies to examine the response of new cotton varieties, particularly Bollgard II to varying irrigation regimes under various row configurations have been carried out. Answers are also sought on the results of applying minimal irrigations to skip-row plantings and on the long term economics of using skip-row cotton within cropping systems.

The focus of the project was on both irrigated and dryland farming systems and was involved with agronomy and physiology to understand water, in a systems context in relation to irrigation, raingrown cropping, crop rotation, fallow, management practice, row configuration etc., using modelling capacity, field research, farming systems approach and adult learning (associated with the RWUE 2 project).

Trials were conducted during 2003-04 and 2004-05 seasons on an irrigated cotton growing property (27° 04.5′ S, 150° 59.7′ E) in the Daandine area near Macalister on the Darling Downs.

The initial objective was to be conduct over a number of seasons: row configuration x irrigation (quantity and timing) x variety (Bollgard II and conventional) x soil type (low and high PAWC soils) trials. Plantings were made in mid and late October 2003 and 2004 respectively to establish a single –skip configuration at 1 m row spacing. Varieties were Sicot 14B (Bollgard II) , Sicot 80 (conventional) in year 1 and Sicot 80B (Bollgard II), Sicot 80 in year 2. The plots received either 1 or 2 irrigations. Detailed crop growth and soil water extraction data were monitored as were yield and fibre quality.

As expected plots receiving 2 irrigations out-yielded those with only one irrigation. The grower co operator estimates the value of the second irrigation to him in 2003-04 was about $1000 per ha for the extra 1.1 ML applied. The project if completed will be capable of examining the economics of various of row configurations, variety, soil moisture , rainfall and irrigations applied.

The 2003-04 trial, in addition to adding to the data set on soil moisture uptake dynamics, provided the opportunity to make a direct comparison between Bollard II and conventional cotton, as Sicot 80B and its “equivalent”, Sicot 80, were planted. Given the same irrigation treatment Bollgard II and conventional were similar in yield (lint bales/ha) and fibre quality although Bollgard II was earlier maturing and appeared to use less soil moisture than conventional.

In both seasons soil moisture was used in and close to the plant line before the middle of the skip, where its use down the profile was rapid as shown by the higher extraction front velocity. There is some evidence that the roots position themselves into the mid-skip area and wait for a plant signal before water extraction commences in that area. Further evidence of this is required and investigations would be assisted by the use of mini-rhizotrons. If this theory is correct, then the search for the switch (fraction of transpirable water in the plant line could be conducted.

More trials need to be carried out so the data set can encompass various climatic conditions and soil types. Then Ozcot can be enhanced and management scenarios investigated. Funding restraints are presently preventing further progress of this work.