The amount of water dedicated to the world’s agricultural activities is huge. It represents 70% of the total used by man, has tripled in volume over the last fifty years and by 2050 is forecast to increase by almost a further 20%. This in the face of intensifying competition from the industrial and domestic sectors.

Many now believe that finding ways to reduce water consumption is one of the principal challenges facing the farmers of the twenty-first century.

It is already the case that, in Europe especially, certain types of agriculturalist are beginning to make greater use of greenhouses and even hydroponics (growing plants without soil) in order to achieve an almost complete degree of control over growing conditions and so save both water and energy.

Automated irrigation systems

For example, greenhouse farmers in the Netherlands use advanced hydroponic systems to grow salad vegetables and flowers in huge quantities for European consumers. These markets are highly competitive, and industrial levels of efficiency are crucial to the survival of such farmers. Modern greenhouses are enormous and have highly automated systems for transporting, watering and spraying plants, as well as for pest control. The most advanced automated growing systems are controlled by intelligent variable frequency drives, which eliminate the need for expensive PLC control systems.

In the mean time, and for the vast majority of traditional crop farmers, there is the issue of irrigation.

About 40% of the world’s food derives from irrigated land. In South East Asia in particular, the twentieth century’s soaring food demands were in part met by a massive investment in irrigation systems. The efficiency of these systems, however, is low: less than two-thirds of the water applied is actually used by the crops.

How can the issue of sustainable water management be reconciled with the continuing use of irrigation to support crop production – even as that production grows in line with population trends? How can greater yields be achieved with less water?

The efficiency of automation in irrigation

Improving efficiency and reducing waste will go at least some way towards squaring the circle. And in this context, as in most, automation is a natural route towards the achievement of both.

The idea of automation in irrigation is neither new nor, in itself, dependent on modern technology. Buried clay pot networks, for example, were used by both the ancient Romans and the Chinese as a way of getting the most out of limited water supplies. The practice is still widespread in parts of South and Central America.

According to this idea, unglazed, porous pots are buried in the ground and filled with water which then seeps at a slow rate through the clay walls into the crop-supporting earth. The pots may be connected by pipes to a constant-level reservoir. Despite their obvious limitations, buried pot networks have a naturally high efficiency because of the way in which the movement of water – through osmotic pressure and capillary action – is directly influenced by the demands of the plant.

For all their power and scalability, modern automated systems, with their electrically-powered motors and pumps, can seem comparatively unsophisticated. Simple examples use timers or volume-controlled metering valves to limit the flow of water. Where such systems are open-loop, however, the potential for waste is obvious.

Automated irrigation systems with moisture sensors

Without some kind of feedback into the irrigation system, watering behaviour is fated to be approximate. Nothing could be more inefficient than an operation that, come an evening of unexpected rainfall, pumps on regardless.

Thanks to falling costs, however, and following much research, more and more irrigation systems now regulate distribution in the light of sensor-derived data, whether those data be water levels, temperature readings, weather conditions or other environmental factors.

Moisture sensors, to take the obvious example, may be stationed in the root zone of crops in order to determine the soil’s volumetric water content. Depending on the technology used, they do this by measuring its dielectric constant or its hydrogen content. Of the former, capacitance sensors are particularly inexpensive and easy to use, although their accuracy benefits from specific soil calibration (clay, for instance, being a better conductor than sand).

Sensors like these are used to transmit data wirelessly to the system’s control unit so that, once water levels drop beneath or rise above certain thresholds, the appropriate response may be carried out by the system’s pumps and valves.

An alternative model regulates the watering of crops in accordance with the fluctuating temperature of the plants’ aboveground portions (canopies) as measured by infrared thermometers.

And in more advanced systems, both drone and satellite technology have been adapted to deliver high-resolution scientific imagery to irrigation control centres. These pictures are considered particularly useful as snapshots of varying moisture or temperature (or even disease) levels across vast areas.

It is not just information about water requirements that is fed back into the irrigation system. Other parameters, such as flow rate, water pressure and pH levels, all benefit from in-built monitoring so that performance can be optimised and problems such as leaks detected and eliminated. Constant water pressure and set flow rates are made possible by motors using variable frequency drives, another example of technology increasingly affordable and available to today’s irrigation engineers.

Energy efficient irrigation system

Supervisory control and data acquisition (SCADA) systems are now being used to integrate and process the data needed to maximise the efficiency of irrigation systems. Already widely used by canal and reservoir operators, they are becoming increasingly accessible to individual farmers. The mass of information SCADA systems typically handle – historical as well as real-time – is combined with data analysis tools managed through graphical user interfaces.

It is a long way from buried clay pots. And yet, in a curious way, the more intelligent the automation, the more closely the irrigation resembles the ancient system’s plant-responsive drip-feeding than it does the crudely intermittent flooding mechanisms of a later age.

The irony – and the challenge – is the price tag. The fully automated system’s hardware and software requirements are far beyond the budget of most small-scale crop farmers. Only the largest commercial outfits could countenance investment in all the technology outlined above.

Having said that, the technology of automation in this area represents a broad spectrum. Thanks to solar panels, even small cultivators way off the grid are feeling the benefit of basic versions. The principle is the same. And where that principle appeals to the good business sense of every kind of farmer, it at the same time results in sustainable water management by all.