Potato grower Robin Griffiths of Duncote Farm in Shropshire said: "This is helping me to transform the way I farm.
"Previously, my harvest estimates were based on manual measurements and a fair amount of guesswork, but now we can get an accurate calculation simply by taking a phone into the field."
The app is described as "sitting on top of" the developers' PC-based i-crop water management tool, already available to PepsiCo's 350 UK contract potato growers.
The company's efforts to reduce growers' water use were acknowledged earlier this week when it was presented with the Stockholm Industry Water Award.
The award's jury praised the company for "saving water all along its agricultural supply chain".