Irrigated UK wheat: A folly or the future?

On average in the UK, about 10% of wheat yield is lost due to insufficient soil moisture. With that figure far higher in the driest years, some farmers are looking at irrigation infrastructure and asking whether wetting wheat will pay. AHDB Knowledge Exchange Manager Teresa Meadows reports.

In the UK, wheat is grown extensively as a rainfed crop. However, about 30% of the acreage is grown on drought-prone soils. As a result, crops can frequently fail to attain their potential output. Water supply does not keep pace with crop demand, especially during the critical stages of yield formation.

The most sustainable response is to invest in cropping resilience. Selecting deeper-rooting varieties and giving crops every opportunity to extend those roots – by width and in depth – to tap into every drop of available water.

Despite such efforts, suboptimal water supply continues to peg back yields. After dry springs over the last two years, with the wheat price around £200/t and climate change increasing the frequency of extreme weather events, some wheat growers are looking at the economic viability of irrigation.

Economic modelling of milling wheat grown on a sandy loam soil in the East of England suggests irrigation can pay – in some scenarios, at least.

In the model, crops were irrigated with an overhead mobile hose reel–rain gun system. This drew water from either a river or a reservoir.

Only where there was irrigation equipment and ‘unused’ summer water available did the approach bring reasonable returns. The Added Value of Water (AVW) ranged from 0.24–0.32 £ m⁻³.

Investment in new irrigation schemes was found to be marginally viable, if ‘unused’ summer river water was available for direct abstraction (AVW = 0.08 £ m⁻³). Unsurprisingly, investments in new farm reservoirs were not deemed profitable (AVW = –0.23 £ m⁻³).

Working with AHDB, ADAS, PrimeAg and Giles Dadd Associates, a group of UK growers has measured natural inputs (e.g. solar radiation, temperature and rainfall) and analysed soil and crop tissues to investigate how to release their crops’ full potential. With agronomy and nutrition already optimised, these discussions provided useful clues.

For farmer Jeremy Durrant (EW Davies, Essex), the main limiting factor appeared to be a lack of available soil water. In 2020, a tramline trial established whether irrigation would boost yields.

A 36 m tramline was irrigated (12 May–1 June) on a 200 m irrigation run, with the rest of the field left unirrigated. In total, 70.4 mm of water was applied.

Irrigation resulted in significant differences (in this relatively dry season), with a 2.14 t/ha average yield uplift in the irrigated area (average field yield = 11.66 t/ha). 

Jeremy said: “If soil type is taken into account, the difference was starker. The irrigated strip included alluvial soils, which showed relatively small differences. However, it also ran into the sands/gravels, which are more typical of the rest of the farm. Here, irrigation had the greatest positive yield impact.”

Figure 1. Biomass map on 25 June 2020 (left) and yield map for harvest 2020 (right) covering irrigated and non-irrigated areas at a farm in Essex (EW Davies)

With proof of concept clear, many questions remain, such as:

• When does irrigating wheat pay?
• How should irrigation be scheduled (e.g. timing, frequency, rate and total amount applied)?
• What influence does the soil type have?
• What is the best equipment (e.g. gun vs boom)?
• How should it be prioritised (e.g. in relation to high-value crops)?

AHDB enlisted the support of Jerry Knox, Cranfield University, to help answer some of these questions in a series of farmer-led tramline trials. These are currently in the ground in the East of England and cover a variety of soil types and rotational situations.

Each tramline trial has been established on the most uniform field available. With an emphasis on timing and rate, irrigation is being applied in response to trigger soil moisture deficits (SMD) for the dominant soil texture.

Crop and weather assessments and irrigation details are being recorded. Yields will be assessed shortly after harvest.

It is important to be clear that these efforts aim to help establish the potential to irrigate wheat in the UK. However, water supplies and how they are used are important strategic topics of conversation.

Widespread adoption of wheat irrigation is likely to be many years off, if it ever happens at all. In a severe drought year, competing priorities are likely to rule out the option, in most situations.

However, knowing the potential and the limitations associated with the technique will help build knowledge resilience. Should the wheat price drive higher, available soil moisture fall lower, and resource (infrastructure, skills and staff) be in place, such an understanding is not a bad thing to possess.