Over the past 70 years the levels of crucial minerals in our basic foods have declined significantly. This is bad news for consumers in the west, but potentially deadly news for those in the developing world who cannot afford a perfectly balanced diet. Dr Steve Hillier from the Macaulay Land Use Research Institute introduces the National Soil Archive, stored at the Institute’s Craigiebuckler site, and explains its importance in monitoring the quality of the soil we produce our food in during BBC Radio 4’s ‘Costing the Earth’ with Alice Roberts, originally broadcast on Monday 28th September at 9pm.