Water remains a key issue for the cotton industry, with improving water use

efficiency a priority. Relatively water research has focussed on the plant and its interaction with the soil and climate. Currently deficit irrigation and many different row configurations are used in the cotton industry without accurate knowledge of how these irrigation regimes affect root development. Water deficit and irrigation an influence cotton plants root systems: dryland cotton has deeper roots than fully irrigated crops and the timing of first irrigation can be used to encourage good root development. These affects are important in overall plant responses to moisture stress.

This project built on the outcomes of the research project CRC 79 “Water relations of the cotton plant”, continuing to investigate the relationship between soil water and plant stress over a wider range of climates. We investigated plant responses to soil factors through assessment of root exploration between cotton varieties, plant water uptake and the response of cotton to normalised soil moisture deficits (FTSW). This project contributed to knowledge of the effects of soil type, temperature and climate (humidity/evaporative demand/vapour pressure deficit) on cotton plant stress. To accurately detect differences in water use efficiency in cotton varieties, new techniques for measuring differences in root development are required; especially for larger scale screening of breeding lines. Field assessment to detect differences in varietal root development was not successful however glasshouse studies found differences. There is also potential for collaboration in developing molecular techniques / microarray and improving in‐situ field root measurement to identify

cultivar differences. Future work on this subject will be supported by the CBA JV water use efficiency and stress tolerance initiative.

Studies into environmental influences showed that changes in vapour pressure affected the level of stress a plant regardless of the level of soil moisture, highlighting the need for irrigation scheduling to reflect both factors. Current irrigation strategies rely strongly on assessment of soil moisture content by probes or using strategies that have relied on monitoring soil water. However, as growers strive for and obtain higher yields and improved WUE, the interaction between irrigation timing and plant stress becomes more critical. Results from this project,

Steve Yeates and Dirk Richards’s research have indicated an exciting opportunity to refine irrigation scheduling to help reduce the effects of stress during periods of high evaporative demand and particularly save irrigation during periods of low evaporative demand. The new ‘Dynamic Deficits’ project will focus on irrigation strategies to maximise

water use efficiency. It will investigate approaches to irrigation scheduling that take into account plant stress, soil water and climate utilising the knowledge gained in this project about the importance of the impact of vapour pressure on plant stress and water use.