Four Norfolk farmers are helping Walkers Crisps in a drive to cut carbon and water use by 50pc within five years.

The '50 in 5' initiative launched by global food giant PepsiCo will encourage 350 farmers to grow potatoes, oats and apples with a lower carbon footprint.

PepsiCo, which employs more than 5,000 people in Britain and runs the world's largest crisp factory at Leicester, has set an ambitious target to reduce environmental impact by half by 2015.

It calculated that the amount of carbon used to grow crops for Walkers Crisps, Quaker oats and Copella apple juice at Boxford, Suffolk, was equal to the amount used by its factories to process products.

Growing the potatoes and sunflowers – key ingredients in Walkers Crisps – accounted for 34pc of the carbon footprint of each bag.

In November last year, a number of farmers were invited to take part in the process to develop smarter ways to produce crops and minimise impact on the environment, said Dan Hewitt, of North Norfolk Potato Growers.

He had been invited to join a group in Switzerland last November on the 'start of this journey' to develop a practical working model and a total of 22 crops were involved in this summer's trial.

Broadland farmer Nick Deane, of Barton Turf, also hosted a trial in a 40-acre crop of potatoes for the i-crop project.

Mr Hewitt welcomed the challenge for the independent group, which is based at Alby, near Aylsham and is a significant supplier of crisping varieties to Walkers Crisps.

Another of the four pilot growers in Norfolk, Cargill Farms at Caister, near Great Yarmouth.

David Cargill's Nova Scotia Farm supplies about 6,000 tonnes of potatoes a year. It has been supplying crisping potatoes for 48 years.

Mr Hewitt, managing director, said that the industry had to raise to the challenge by developing i-crop, which is a web-based crop management system. This will enable all farmers from next year to monitor inputs, including water use, manage crop progress and calculate carbon emissions.

'We are a fairly major partner in the i-crop programme with PepsiCo and we've been monitoring four crops on a week-by-week basis and using an advanced weather station to record data.

'Frankly this is the start of a journey and it is a multi-year project for PepsiCo. It will gain strength and we're working hard with them to make it happen.

'We can see some clear benefits going forward. It is an on-going process and we're quite excited,' he said.

Mr Hewitt said more accurate information would help growers but it was a big challenge.

He said: 'We all sit and think that we're doing things very well but we need to challenge ourselves.'

And the use of water was a big issue, said Mr Hewitt.

Soft fruit growers had used trickle or drip irrigation systems with great success and Tim Place, of Place UK at Tunstead, had cut water use by about 40pc with an award-winning scheme.

However, these kinds of systems are not yet feasible for potato growers. Mr Hewitt said: 'We've got to start thinking about things like drip irrigation.

'At the moment it is cost prohibitive for potatoes but in three years, who knows. 'It is a challenge from PepsiCo globally for us to be more inventive about how we grow potatoes.

'North Norfolk is a prime producer of potatoes and there are some very good potato producers within the county. But, I would still say we need to challenge ourselves.

'Water is going to be a finite resource and if we can cut the water use by 50pc in the next five years, that's fantastic.'

The i-crop will also encourage farmers to use more fuel efficient tractors and machinery.

Specialist researchers in potatoes at Cambridge University Farms (CUF) have also been advising the project and a board member of NNPG, Jamie Harrison, is chairman of the grower-funded body, CUF.

Mr Hewitt said: 'We look at their best practices as a group and we trial these best practices every year.

'It is not even farm specific, it is down to field and variety.

'We've got to look at each field and its history as we do and challenge the recommendations, so it might be possible to cut nitrogen or phosphate.

'We're trying to demonstrate that we are using our inputs to the optimum.

'And you need to challenge, stretch it and see where the weak points are. 'But if means using an extra 20kg of nitrogen to get another six tonnes of yield, then it makes sense.

'It is a challenge to the entire industry and we've got to rise to it.'

He added that the established crisping varieties, for example Saturna and Hermes, which were introduced about 15 years ago, have done a good job but new varieties were coming forward.

Mr Hewitt said: 'We've been testing them over the past three years.

'PepsiCo has some very interesting varieties and we're truly looking forward to working with them from what we've seen so far.'