Among the many thousands of different forms of farming – no two farms can ever be the same – we can discern six main kinds of enterprise. The traditional three, the mainstays, are arable, livestock (traditionally called “pastoral”), and horticulture. Plantations including orchards may be said to form a separate, fourth category. More generally, all of the above can be integrated into one or several of the many forms of agroforestry (including forest gardening), which combine farming and trees synergistically. Finally, much of the world including Britain has largely neglected aquaculture, the management of water in all its forms for productive purposes. Aquaculture becomes more and more pertinent as lakes are drained and aquifers dwindle and climate change plays havoc with rainfall, and sea levels rise. Britain in particular has yet to learn to cope with drought and flood. David Cameron’s promise of more sandbags in the spring floods of 2014, and his repeated, fulsome praise for the emergency services, will not do.

Finally, agroecology comes into its own when several or even all of the enterprises are combined in one integrated holding; the mixed farm. But we cannot sensibly classify mixed farming as a seventh kind of enterprise, since it is by definition a combination, or rather a permutation, of the others.

All kinds of farming, however, depend absolutely on the physical environment: the soil; the water supply; the latitude and altitude; the weather and the climate (not quite the same thing); and the topography. We should look at these first.