Make every drop of water count

Precision techniques are enabling skilled farmers to achieve optimum use of water to grow high-value quality crops for today's retailers.

Growers were showing keen interest in drip or trickle systems at a national irrigation demonstration held on part of Lord Iveagh's Elveden estate, near Barton Mills.

Irrigation specialist Richard Relph, who was a large-scale potato grower in Shropshire, explained the thrust of Field GB's effort to make every drop count by getting water to the crucial root zone. This approach avoided potential waste by over-application from rain guns, booms and conventional hosereel systems, he argued.

The latest design of drip irrigation enabled a precise volume of water to be applied from as little as 1.5mm an hour, which gives even more flexbility for accurate crop management.

Traditionally, rain guns throw big volumes of water into the air, often applying 25mm or an inch at a time and this will result in loss, run-off or percolation below the crop's root zone on some soils, said fellow regional irrigation specialist, George Darling, who is basded at Taverham, near Norwich.

Mr Relph stressed that drip irrigation was not a cheap option and thus not ideal for all growers. First, 11,000km of T-Tape had to be laid to irrigate one hectare of potatoes and this would have to be replaced at the end of the season.

It would cost around £163 an acre if drip or trickle irrigation was installed but Mr Relph stressed that part of the investment involved the purchase of the key header supply network, which would last many years. Where trickle had been used, it was often laid out in blocks of eight acres, which could then be irrigated using a low pressure system in rotation.

With the growing energy cost of pumping water through a network of pipes, then a drip system requiring pressure of less than one bar was a major advantage given that a typical rain gun and hose might be running at eight or 10 bar pressure.

One south Lincolnshire grower, David Matthews, who grows 300 acres of potatoes with trickle irrigation around West Pinchbeck, Spalding, was convinced of the advantages because it has further improved crop quality and returns.

National irrigation specialist Jerry Knox, of Cranfield University, said growers had to decide which system was best suited to their business and cropping systems. “There are disadvantages with trickle or precision - not least the cost of replacing the tape each year and that it inherently needs a very high level of management and skill. It is not just a system that can be put down and then swtinched on and off.”

“There is also the risk that a farmer will have invested in drip systems which are then not fully used. At least if you have a rain gun, you've got it for the next year,” he added.

Dr Knox, who was involved in a two-year intensive study on several farms in East Anglia, estimated that 75pc of the irrigated land in England Wales extending to some 147,000ha, relied on rain guns. When irrigation was not available, there were significant reductions in yield and grading quality of between 12pc and 18pc on carrots.

However, Dr Knox's research team, which looked at crops on Breckland farmer Tim Jolly's enterprise at Roudham, near Thetford, identified big ranges in irrigation performance. He urged farmers to check the effectiveness of their irrigators - by laying out a line of baked bean tins - and then measuring the amount of water, a measure of uniformity could be assessed.

For many growers, especially with smaller acreages, then a boom or rain gun made the most sense. Irrigation consultant Bill Basford, of Southwell, Nottinghamshire, said: “The boom costs about £10,000. If you look at that over a 10- year life and depreciate over the seasons and over 50 or 60 acres, it probably costs about £30 an acre per season.

“That is easily recoverable with increased quality and even with the extra time it takes to fold and move the boom.

“Typically, it will cost about £14,000 or £15,000 for a rain gun but in fact, they've stayed very competitive. Now, they're very sophisticated machines with good electronic control and computer management. Very reliable really,” said Mr Basford, who worked for Adas until retiring at the age of 60 two years ago.