Free The Knowledge: How to Rebuild Our World From Scratch by Lewis Dartnell Page A

deficit in the balance sheets.
    Modern industrialized agriculture is astonishingly successful, with an acre today producing two to four times more food than the same land provided a hundred years ago. But the only way that farms today can function, growing dense monocultures on the same land and still producing high yields year after year, is by spraying potent herbicides and pesticides to maintain an iron-fist control over the ecosystem, and by the liberal application of chemical fertilizers. The nitrogen-rich compounds provided in these artificial fertilizers are created industrially by the Haber-Bosch process, which we’ll return to in Chapter 11. All of these herbicides, pesticides, and artificial fertilizers are synthesized using fossil fuels, which also power the farmyard machinery. Ina sense, then, modern farming is a process that transforms oil into food—with some input from sunshine—and consumes around ten calories of fossil fuel energy for every calorie of food actually eaten. With a collapse of civilization and the disappearance of an advanced chemical industry, you’ll need to relearn traditional methods. Today, organic produce is the preserve of the wealthy; in the aftermath it will be your only option.
    We’ll come back later in this chapter to how you can maintain soil fertility over the years. Let’s start with the fundamentals of cultivating crops from the ground up.

WHAT IS SOIL?
    As a farmer, you have only limited control over nature. You obviously cannot control the amount of sunlight beaming onto your fields: you can’t change the climate of your region or dial in the seasons. You also can’t control the rainfall, although you can regulate the moisture content of your fields by balancing irrigation and drainage. The one thing you have most control over is the soil: you can chemically enrich it with fertilizers, as we’ve just seen, and physically manipulate it with tools like the plow. So the most fundamental element of agriculture under a farmer’s control is the soil, and that requires an understanding of what soil is, and how it supports plant growth.
    All the civilizations of history owe their existence to this thin scraping of topsoil. Hunter-gatherers can support themselves by foraging in woodlands, but cities and civilization rely on the enormous productivity of cereal crops—shallow-rooted grasses that are utterly dependent on the resources provided by topsoil.The basis of all soil is disintegrated rocks that make up the crust of our planet. Rock is physically attacked by flowing water, blowing wind, and grinding glaciers, and chemically weathered by weakly acidic rainwater thatdissolves a little carbon dioxide as it drops from the clouds. Depending on the degree of crumbling, this produces gravels, sands, and clays. These particles are stuck together with humus—a matrix of organic matter that helps retain moisture and minerals, and gives topsoil its dark color. Soils typically contain between 1 and 10 percent humus, although peats approach 100 percent organic matter. But, most important, soil hosts a huge and diverse population of microbial life, an invisible ecosystem that processes decaying matter and recycles nutrients for plants.
    The main factor that determines the nature of a particular soil and its appropriateness for different crops is the proportion of different particle sizes: gritty sand, intermediate silt, and fine clay. It’s easy to get a visual check on soil composition. Fill a glass jar one-third of the way with soil (picking out any hard clumps, stems, or leaves) and top it off almost to the brim with water. Screw on a lid, and shake vigorously until all lumps have been broken up and you have a uniform muddy soup. Let the jar stand undisturbed for a day or so, allowing time for the suspension to settle back down and the water to be nearly clear again. The different grains will have sedimented out in order of their particle size to show distinct layers or bands.