THE PRINCIPLES OF COTTON WATER RELATIONS AND THEIR APPLICATION IN MANAGEMENT
Mar 10, 2017

Agronomy & physiology WCRC Agro-physio-australia WCRC1
Abstract                                                                         Back to Table of contents

The keys to understanding the principles of water relations that are specific to cotton are found in: (i) the ecology of the wild ancestors of cotton  (xerophytic shrubs), (ii) the basic pattern of development (the orderly and regular production of mainstem nodes, lateral fruiting branches and fruiting sites, and the progression at each fruiting site from floral bud through to open boll or shed fruiting form), (iii) relative sensitivity of these developmental processes, and the growth physiological processes, to water stress. The biological and agronomic responses to variation in water supply are reviewed and interpreted in light of this understanding.  Cotton is well adapted physiologically for both rain grown and irrigated production, and economically for both production on plantations and small holdings.  The relative importance of rain grown and irrigated cotton on a global scale are considered.  The management requirements of each in respect to optimising use of water discussed.  Effects of excess water (water logging) are as important as water deficits.

Technological developments relevant to water relations can be broadly classified as software (rules of thumb, indices, plant mapping, osmotic adaptation, computer models and decision support systems) and hardware (neutron probes, pressure chambers, infra-red thermometry, drip irrigation, lateral shift and centre pivot irrigation). Their use in management and research applications is discussed.  Management should aim to optimise the use of limited water resources, be it rainfall or irrigation supply, by maximising returns per unit input and minimising environmental impact.  Management decisions have to be made at policy, strategic and tactical levels and appropriate software and hardware selected. There are specific important challenges and opportunities: management of limited irrigation water supplies; environmental impact of irrigation on salinity, and pesticide and nutrient pollution; the use of urban domestic wastes and saline drainage water; interaction of water with other factors; and risk analysis.

Conclusions

Modern cultivated cotton species have inherited from their wild relatives attributes that enable them to survive long periods of drought and develop rapidly when water is available, enabling the crop to make full use of variable rainfall or respond well to irrigation.  These attributes are the indeterminate habit and the relative sensitivity of physiological processes to water deficits.  The former confers a flexible morphological and reproductive development and the latter determines priorities for assimilates.  Ancestral sensitivity to the putative wet and dry "signals" from the environment imposes special constraints on management of the cotton crop in relation to water.  Research is needed to see if signals from roots in drying soils found in other crops occur in cotton, and to determine their role in the response of the crop to water deficits, particularly boll shedding, priorities for growth, and the balance of vegetative and reproductive growth.

In order to maximise returns from limited rainfall and irrigation water supplies, research and management should concentrate on improving WUE in its various aspects.  Opportunities exist to improve WUE with:

  • new irrigation technology, or better use of existing technology, in order to reduce application, conveyancing and drainage losses and reduce the E component of ET;

  • use of hardware and software to monitor crop progress for tactical optimisation of irrigation scheduling;

  • identify by using simulation software, and then adopt, robust management strategies for irrigated and rainfed crops that will minimise risk and use maximise return from limited irrigation supplies and rainfall;

  • soil surface management technology to retain rainfall and reduce runoff and soil evaporation;

  • pursuit of genetic improvement of agronomic WUE by improved gas exchange and/or partition of assimilates.


If we are successful in raising WUE we will reap the benefits of higher returns from a limiting resource, with the added potential to reduce contamination of rivers and groundwater and reduce the risk of salinisation.

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