You can't just scatter seeds in a field and ease off on the weedkiller to get an organic crop.

So it takes three years to get an organic crop to equal what a farmer using manmade controls can get in one.

Experts analysed organic crop farming across 17 criteria such as yield, impact on climate change, farmer livelihood and consumer health.

Like other studies, the results show significant variations, with some conventional crops having larger quantities of some vitamins than organic crops.

To begin with, organic fields must go through a cleansing period of three years, without the use of any prohibited substances, before planting the first organic crop.