*7.2. Factors Affecting Trends in WUE*

From the above discussion, it is clear that the trends in the WUE of irrigated agriculture are affected by a range of factors which may be broadly categorized as shown in Figure 7. Engineering and technological factors include improvement of water distribution networks and on-farm irrigation development, irrigation scheduling, real-time control and optimisation, remote sensing and sensor and communication networks. These factors improve irrigation WUE mainly by reducing water losses. In the recent past, a variety of hardware and software gadgets has become commercially available and is used to enhance irrigation WUE. Advancements in plant genetics have led to the development of high-yielding and disease-resistant varieties with higher WUE. There has been greater environmental awareness, leading to some governments around the world funding water-saving initiatives with the understanding that the water saved is released as environmental flows. Socio-economic factors are also important drivers of WUE. This will be covered in this section, with a focus on technology adoption and the decision-making processes of irrigation water users.

**Figure 7.** Factors influencing water use efficiency.

When farmers are faced with limited availability of irrigation water, they have to make challenging decisions on how best to operate. This is a common problem in Australia, where to a large extent, water is the limiting factor of production, but land is virtually unlimited. It is common to see farmers irrigate part of their land and cultivate the rest under rain-fed conditions. A study undertaken in Southern Spain found that the majority farmers growing irrigated intensive olive groves used deficit irrigation in order to maximise the value of limited available water [51].

Some researchers have observed that water saving initiatives have mainly focussed on engineering solutions such as reduction of seepage losses and suggested that further improvement in on-farm WUE could be achieved by the adoption of new irrigation technologies [52]. However, it must be noted that technology adoption is a complex sociological phenomenon, and its success will largely depend on the willingness of water users to change their attitudes. Irrigation water users, like other members of the community in general, are predisposed to continue with the farming practices they are most familiar with, for fear of the unknown. In most cases, water users have access to information on new technologies, but getting people to change their attitudes and adopt new practices or technologies is a slow process. Research undertaken in the United States suggested that the requirement to learn a new set of skills may act as a deterrent to irrigators investing in new technologies or adopting new practices [15].

In both Australia and the United States, the cost of changing to new technologies and practices has been cited as a significant factor causing non-adoption [15,52]. This includes the capital required as well as the associated on-going costs. A typical example is when farmers decide to change from surface irrigation methods to pressurised systems such as centre pivots and lateral move machines which are generally associated with higher WUE. These pressurised systems not only require substantially higher capital costs to install, but come with higher energy consumption and are therefore expensive to run [5].

A European-Union-funded research project undertaken in Italy and Portugal concluded that lack of adequate knowledge and incentives may prevent farmers from exploiting the full potential of available technologies to optimise WUE [53]. The study thus recommended that there should be a continuous knowledge exchange among scientific experts, farmers and other stakeholders, and appropriate support be provided to encourage environmental conservation.

As discussed earlier, one of the main approaches used in Australia to attain increased WUE is the upgrade of irrigation infrastructure and provision of subsidies for on-farm improvements. However, some studies [3] have shown that sometimes these investments are not cost-effective, especially when compared to other alternatives such as water trading which is aimed at efficiently allocating water across competitive use. Therefore, when the economic benefits of these taxpayer-funded initiatives are not apparent, public support is not guaranteed.

It should be noted, however, that WUE cannot be improved infinitely. In the case of an irrigation system that has a lower irrigation performance to start with, it would be easier to notice an increase in WUE when improvements to the system are undertaken. However, for a system that is already operating at or near the optimum level, the WUE will increase (if at all) at a much slower rate. A study conducted in the Guadalquivir River Basin in Spain found that the impact on the WUE of technological innovations, such as deficit irrigation, new crop varieties and other water-saving technologies, had decreased considerably after a number of years [54]. As previously noted, plant breeding has been used for a number of decades now to develop plant varieties with higher WUE. However, this improvement is not expected to continue at the same rate as before [55]. This implies that the world cannot solely rely on the past and the present technologies to improve WUE, but must continue to undertake research to generate newer technologies that can be used to further improve the WUE.
