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Practical solutions to optimise nitrogen use efficiency within modern surface irrigated cotton systems in Australia may be possible by regulating the frequency of water and reducing the N applied, compared with typical current practises. A two-year study examined the effect of irrigating at three different water deficits that applied a similar total irrigation volume: >−60 kPa (HF), between −80 and −100 kPa (IF) and between −100 and −120 kPa (LF) for a period from initial flowering throughout boll development, in combination with different nitrogen fertiliser rates on the growth, yield, nitrogen use efficiency and lint quality of cotton. It was hypothesised that shorter deficits would increase N uptake, and nitrogen use efficiency compared with longer deficits caused by consistently higher soil water potentials in the root zone. The major effects of irrigation treatment on growth was to increase plant height and number of bolls, delay crop maturity and decrease micronaire. The irrigation strategy according to yield was most consistently optimised over both seasons when soil matric potential was maintained between −80 and −100 kPa (IF treatment). Lint yield was reduced by 9–13% when the irrigation deficit was <−100 kPa. The most efficient fertiliser use varied between the two years but was always lowest in the treatment with the highest deficit. Irrigation deficit did not change nitrogen uptake or internal nitrogen use efficiency. Nitrogen, even at rates substantially lower than typically used commercially, did not affect fibre quality. There was no interaction between irrigation strategy and N fertiliser rate on yield, fibre quality and fertiliser use efficiency. • Irrigation at soil matric potential >−60 kPa delayed maturity and reduced micronaire. • Intermediate frequency of irrigation produced optimum lint yield and fibre quality. • Low frequency of irrigation advanced maturity up to 10 days but decreased lint yield. • Reduced fertiliser N rate with intermediate frequency of irrigation optimised NUE. [ABSTRACT FROM AUTHOR]

• A guidelines for high performance bay irrigation. • Higher flow rates and lower irrigation duration can deliver higher application efficiencies. • Preferred flow rates for the major soil groups are recommended. • A simple linear function can be used to estimate the irrigation duration at constant soil moisture deficit. The maximum efficiency attainable by surface irrigation in any particular situation is determined largely by the soil infiltration characteristic and the flow rate onto the field. Performance evaluations have suggested that higher flow rates than those traditionally recommended can lead to increases of about 20% in the application efficiency of bay irrigation across the dairy regions of southern Australia. However, substantially reduced irrigation durations are required to realise these efficiency gains and greater precision is required in the selection and management of these shorter durations. In this paper, infiltration characteristic curves representative of the predominant (cracking and non-cracking) soils of the region are used in the surface irrigation simulation model SISCO, for a range of bay lengths and soil moisture deficits, to determine: (i) the flow rates required to achieve the maximum efficiency on the bay irrigated soils of southern Australia; and (ii) the means for real-time estimation of optimum irrigation durations. The aim is provision of guidance to irrigators seeking higher efficiency through the use of higher flow rates. Real-time estimation of optimum time to cut-off must recognise the substantial variations in infiltration within a soil type and with time due to changes in antecedent moisture content, and hence must be adaptive to the conditions prevailing at the time of any irrigation. A method for estimating time to cut-off (previously developed for furrow irrigation), is extended to the hydraulically more complex case of bay irrigation. The method is based on simple linear relationships between the advance time to a nominated point part way down the field and the time to cut-off. Its application to the management of irrigations is demonstrated using data from multiple irrigations of a single bay under varying soil moisture conditions. [ABSTRACT FROM AUTHOR]

The demand for fresh water is on the increase, and the irrigation industry in Australia is looking to a future with less water. Irrigation consumes the bulk of the water extracted from various sources, and hence the efficiency of its use is of outmost importance. This paper reviewed the advancements made towards improving irrigation water use efficiency (WUE), with a focus on irrigation in Australia but with some examples from other countries. The challenges encountered, as well as the opportunities available, are also discussed. The review showed that improvements in irrigation infrastructure through modernisation and automation have led to water savings. The concept of real-time control and optimisation in irrigation is in its developmental stages but has already demonstrated potential for water savings. The future is likely to see increased use of remote sensing techniques as well as wireless communication systems and more versatile sensors to improve WUE. In many cases, water saved as a result of using efficient technologies ends up being reused to expand the area of land under irrigation, sometimes resulting in a net increase in the total water consumption at the basin scale. Hence, to achieve net water savings, water-efficient technologies and practices need to be used in combination with other measures such as incentives for conservation and appropriate regulations that limit water allocation and use. Factors that affect the trends in the irrigation WUE include engineering and technological innovations, advancements in plant and pasture science, environmental factors, and socio-economic considerations. Challenges that might be encountered include lack of public support, especially when the methods used are not cost-effective, and reluctance of irrigations to adopt new technologies. [ABSTRACT FROM AUTHOR]