Here, where the soil is exposed to rain and wind erosion, nitrogen and other water soluble nutrients are washed away. In a field of wheat all the plants have the same nutritional requirements, their roots occupy the same levels in the soil and will only be able to obtain nutrients from this one level. In a perennial system some plants will have deep-root systems and these will get many nutrients from deep down in the soil in areas beyond the reach of other plants. While deep-rooted plants make hidden nutrients accessible to other plants, and to us, most nutritionists recommend diets that not only include perennial fruit and nuts, but also annuals like beans, lentils, rice and oats. Organic farming may not be the ultimate ecological model but it delivers the foods we want to eat such as potatoes, courgettes, sweetcorn and so on.
Perennial agriculture means a whole new larder of tastes and textures to get used to.
For a nation of conservative stomachs it might be a gastronomic leap too far. But, according to Fern, we are missing out on nutritious foods which could help prevent disease and common ailments. The sea buckthorn is a good example. Commonly grown in China as a commercial crop, it is the most nutritious fruit in the temperate zone, but is rarely eaten here. Thousands of species of edible perennial plants can be grown in Britain yet most people are only aware of the 30 or so found in the greengrocers.