The problem of agriculture
Since its inception, agriculture has relied on annual plants that are grown from seed every year and harvested for their seed. That requires tilling of the soil, which can be done on a small scale without causing great harm, as in small, intensively hand-managed plots or on annually flooded land along a river. But every civilization that has practised tillage on a large scale has suffered the often catastrophic consequences of soil erosion [1, 2]. Industrialization has compounded the problem through burning fossil fuels and chemical contamination.
The world’s natural landscapes are covered mostly by perennial plants growing in mixed stands [3], w hereas more than two-thirds of global cropland is sown to monocultures of annual crops . Conversion from natural to agricultural landscapes dramatically alters ecological conditions. Across the planet, more land has been converted from perennial to annual cover since 1950 than in the previous 150 years. This recent expansion of cropland has made it more and more necessary to apply chemical fertilizers and pesticides, which disrupt natural nutrient cycles and erode biodiversity [4, 5].
Perennial plants are highly efficient and responsive micromanagers of soil, nutrients, and water. Annual crops are not; they require churning of the soil, precisely timed inputs and management, and favourable weather at just the right time. With shorter growing seasons and ephemeral, often small root systems, annual crops provide less protection against soil erosion, wasting water and nutrients, storing less carbon below ground, and are less tolerant of pests than are perennial plant communities [6].
Today, vast swaths of entire continents have been scoured of their perennial vegetation, leaving the soil uncovered for a good part of the year. Even when the soil is covered during the growing season and even under organic management, lightly rooted annual crops fail to manage water and nutrients the way their deeply- and densely-rooted, persistent perennial antecedents did. Agriculture’s destruction of perennial root systems has wrecked entire underground ecosystems, subtracting from the soil much of what makes it soil.
Agriculture is a problem older than history. It has always depended largely on annual grass and legume species that humans domesticated between 5000 and 10 000 years ago. That domestication of annuals set in motion a somewhat ironic series of events. First, annual grain crops made civilization both possible and necessary. Much later, civilization - largely through exploitation of fossil fuels and synthetic chemicals - created conditions under which agriculture could become both extraordinarily productive and ecologically destructive. But today, it is the fruits of the very civilization made possible by agriculture - scientific knowledge, data, and techniques - that have clearly revealed to us both the necessity and the possibility of correcting the well-intentioned wrong turn our species made 10 000 years ago [7](Jackson, 1980).
