Is it worth irrigating wheat?

Recent dry springs have triggered an AHDB investigation into the potential to irrigate wheat. Andrew Blake reports.

Is wheat worth irrigating?

With nearly a third of the UK’s wheat crop grown on droughtprone land, a series of farmer-led tramline irrigation trials is underway in partnership with Cranfield University.

The university’s Prof Jerry Knox says: “On average we think about 10,000 hectares of the country’s wheat is irrigated each year, mainly to preserve grain quality, but that figure does oscillate depending on summer rainfall.

“The area is small compared with the 150,000ha typically irrigated for all other field vegetable and potato crops, but there can be appreciable yield responses in wheat to relatively small volumes of irrigation water, typically up to 50mm in a dry year.

“Irrigation is an expensive and time-consuming operation. So, we need to provide advice that is robust and relevant for growers.”

The publication ‘Irrigated Crops and their Management’, written by ADAS’ Roger Bailey and published in the 1980s, suggested various soil moisture deficits which might trigger cereal irrigation on specific soil types.

However, there is a complete absence of recent published information for UK wheat production about how much water is required; when it should be applied and how; the influence of soil textures on critical trigger thresholds, and the economics for modern varieties, adds Prof Knox.

Trials

To help fill those knowledge gaps, seven farms in East Anglia and Yorkshire have agreed to become involved in what he describes as ‘scoping trials’.

They are on a range of soil types – clay, light sand/gravel and fenland.

AHDB’s Teresa Meadows says: “On average, research shows about 10% of UK wheat yield is lost due to insufficient soil moisture.”

Economic modelling of milling wheat grown on

Prof Jerry Knox E.W. Davies Farms has trialled irrigating wheat.

In the field Ben Martin, Suffolk

JBen Martin manages 1,300 hectares of blowing sand to loamy sands over chalk at Moulton Manor Farm, near Newmarket in Suffolk, where the 20-year average annual rainfall is 634mm.

He says: “We are very well invested in irrigation equipment and infrastructure – 14 reels, of which eight are 72-metre Briggs booms, and six rain guns, two of these fitted with GPS section control.

“We run Raindancer GPS software on each machine which gives us remote control of the reels and the ability to apply water at variable rates. We have a mixture of boreholes, reservoirs and river abstraction licences.

“We normally irrigate some of our wheat area each year, the

sandy loam has suggested that irrigating wheat can be rewarding, but only where farms already have the necessary equipment and ‘unused’ summer water is available, she adds.

“All seven farms already have irrigation equipment and abstraction licences for water – some have a root crop rotation; others are irrigating just cereals.”

The hope is that their experiences in 2021 and feedback will help answer several key questions (see panel, below).

Trials questions to be addressed

rHow much and when does irrigating wheat pay yield dividends? rWhat influence does soil texture have? rHow should irrigation be scheduled (for example, timing, frequency, rate, and total amount applied)? rHow should irrigation be prioritised in relation to high-value crops?

percentage depending on the pressure on our system from the potatoes and other high value crops.”

Wheat and other cereals are usually irrigated at the end of April to early May before the vegetables.

“Where we’ve irrigated part fields, we’ve recorded a yield response of 20% plus,” Mr Martin says. For this year’s trial a soil moisture deficit probe is being inserted into a wheat field and a 72m boom width

In the field Jeremy Durrant, Essex

JEssex-based Jeremy Durrant is among the farmers involved in the scoping trials.

Miss Meadows says: “Working with Jeremy and others, it became evident that there were questions that hadn’t yet been answered.

“With irrigating of cereals potentially becoming more important in the years ahead due to increased drought frequency, it seemed like a good opportunity to start the conversation.”

Over the past six years, annual rainfall at the 1,300-hectare E.W. Davies Farms, based at The Hydes, Thaxted, has been 50mm lower than the long-term average of 550mm, says Mr Durrant.

He grows mainly combinable crops, maize and sugar beet, his water source being spring-fed reservoirs with a summer abstraction licence for 205,000cu.m.

Probes

“We’ve used probes for 10 years or so to monitor what’s going on with soil moisture and rooting and most years they show we are moisture limited,” says Mr Durrant.

“Last year was the first that we trialled irrigating wheat. We have always thought there would be a benefit, but with ADAS’ Yield Enhancement Network suggesting that on our soil type, predominantly Hanslope clay, we were not moisture limited, we wanted to see for ourselves whether this was the case.

“We trialled a small area, applying 75mm in four weekly passes from mid-May and saw an average yield gain of four tonnes/ha.

“We have purchased some cheap second-hand rain gun equipment and will expand the area to cover up to 100ha.

“The area and the amounts of water applied will depend on rainfall and moisture probe data. We want to try to learn optimum

area is being irrigated at a predetermined SMD trigger point.

“We’ll work with the Soil Moisture Sense company to establish and monitor the trigger point,” he adds.

“I hope to learn how to better target wheat irrigation and take some of the guesswork out of it by using soil probes to give me exact trigger points linked to soil moisture – and then matching these to when the wheat plant has a high demand for water.”

Rising world wheat prices would make irrigation more economically feasible, he adds.

“However, making sure the wheat crop and the soil it’s grown in is as resilient as possible has to be the first consideration, with irrigation used as a tool to then help the crop reach its full potential.

“It’s unlikely we’ll ever have access to more water, so building our soils’ resilience to drought by increasing its organic matter and using the water we do have in the most efficient and targeted manner is our main focus.” timings and amounts.”

A rain-fed unirrigated control tramline will be left at each pass.

“This way we can start to see if there is any economic benefit,” he says.

“Last year was about proving to ourselves that moisture was a limiting factor and seeing if we could do anything to remove that variable. This year we’re looking more at timings and quantities to get the biggest economical response.”

Higher wheat prices will clearly make irrigation easier to justify, he adds.

Browse, list and apply for hundreds of the latest Arable roles at jobsinagriculture.com