Open day shows benefits of drip irrigation

A recent open day organised by Howseman Agriculture and Netafim on the silt soils north of Holbeach in Lincolnshire demonstrated how effective drip irrigation can be for potato production.

Although the event, hosted by Loveden Estates, occurred just a couple of weeks after torrential rain hits parts of the county, Andrew Howseman, founder and proprietor of Howseman Agriculture said that he believed that the irrigation technique would still deliver benefits to the final crop.

“I don’t think, on this land, that we will see a big yield difference, but drip does provide an improvement in shape and quality,” he stressed. “Better scab control is also a benefit.” In fact Andrew believes that the key benefit of drip irrigation over other techniques such as rainguns and booms is that it makes the field (and therefore the crop) more even across the different soil types which will be present.

“Drip evens things up which, in my opinion, is where you get an overall yield benefit across the field. It is due to a combination of all the marginal gains that you get: crop quality, less labour, etc,” he continued. “There can be issues with greening and removing tape, but most of these can be overcome with care and planning. Drip irrigation requires a different mindset and once people get that, they focus on the benefits.”

The system at Dawsmere takes water from a hydrant at the side of the field, which is fed from a reservoir via a ring main, and at this point a Netafim filter system had been installed. “It’s a bit like a tractor air filter,” explained Andrew Issott. “You have a broad mesh which takes out any larger particles, and then two finer ones. When you get a pressure differential between the out and inner section it will self-flush: It rotates and sprays the gauze with water to clear it.” The resulting water and debris is then discharged via an additional pipe, for example back into the dyke. “We tend to set a pressure differential of around 1 bar, so as soon as you get any blockage it will clean itself out,” he added.

At Dawsmere the water from the ring main is fairly clean, but where people are pumping out of a dyke for example, such a filter system, with a basket or gauze fitted over the intake, is a big benefit. From the filter the water passes down the lay flat pipe at 3 bar to the valve which switches between the three sections of irrigation and the pressure is taken down to about 0.8 bar which is what the tape runs at.

In the crop three 300m irrigation blocks had been set up; two running in either direction from a main distribution hose, and another further up the field running in just one direction. Each filter has the capacity to run around ten valves at up to 10 bar, with Andrew Issott confirming that the company has a unit operating with nine valves this season.”

One grower present pointed out another big benefit is the reduced labour requirement, and that two people can look after a tape system and check for leaks, but still do other jobs during the day, whereas moving irrigators on outlying rented land can be a full time job in itself. Adding a fertigation unit also allows fertilisers to be added while watering and increases the flexibility of drip irrigation.

Some growers have concerns over how long the tape and header pipes last, but some users report that they are still using systems which are five or six years old without major issues. One weak point can be the plastic fixing which pushes into the header pipe to join it to each tape. “It is designed to break,” points out Andrew Howseman. “However, if a sprayer runs directly over it the spike can push all the way down and puncture the bottom of the header pipe.” Such damage is repairable, but does show the need for regular inspections and checking – which should be the case with any irrigation system.

The biggest perceived benefit of drip irrigation systems is that they use less water, but while there is plenty of anecdotal evidence of this, Andrew believes those selling drip systems should do more to scientifically prove the claims. “In terms of water utilisation, the honest answer is that we don’t know how it compares to other systems,” he admitted. “This year we have lots of people measuring soil and water use in several places, so we will have more data available at the end of the season for a better picture. For years people have been claiming that there is a water saving over rainguns, and some people claim a 25 per cent average reduction over seven years.”

He added, “The big benefit is that the water is going where it needs to be, but we also need to be able to prove that this much more efficient than a hose reel and boom.”

When using any irrigation technique, it is important to assess soil moisture to schedule accurate water application, but this is particularly true with drip due to the targeted nature of the application. There are various types of probe and system for measuring soil water content on the market, but Andrew Howseman stresses, “To me it doesn’t matter what you use, but you need to use something to measure irrigation efficiency.”

He adds that connecting such systems to the pump to turn the irrigation on and off as required might be an option in the future, but cautions that it involves a lot of automation, and that relying on a single probe to determine the irrigation needs of a large field containing various soils types could give poor overall results: “If you are not carefully about the senor and valve positions you could be worse off.”

Another issue reported by growers already using drip, particularly when early weather conditions are dry, is damage to the pipes and tapes by birds and other animals, usually looking for drinking water. “I think we want to be using a Venturi system so that we can put garlic extract or something similar in right from the start of irrigation which would deter damage and drinking in the first place, but until we try it we don’t know how effective such an approach will be.”

With more and more pressure on water resources in parts of the country and the ongoing review of irrigation licensing by the Environment Agency (all users of drip systems will need to have applied for a licence by the end of this year), there is increasing interest in the technique from potato and vegetable growers, and a number of specialist producers are already achieving good results from the technique.