Energy: The Flow That Drives Everything

Where ordinary land use wastes it

The usual way of farming loses energy in three ways.

Sunlight falls on bare ground. A field that lies ploughed and empty for half the year captures nothing during that time. The light that a green cover would have turned into sugar heats the soil instead, dries it out and, on a Mediterranean summer slope, leaves it hot enough to harm the life within it. A single-layer orchard over bare soil uses one floor of a building that could have several.

The stored energy is burned or hauled away. Prunings, straw and crop residues hold the energy that the soil life needs. Where they are burned, that energy is released in minutes as heat and smoke. Where they are carted off, it leaves the land for good. The soil goes hungry, its life thins out, and with it go the humus and the crumb structure that hold water and nutrients.

Fossil energy fills the gap. Industrial farming replaces much of the work the sun and the soil life used to do with energy from oil and gas. An FAO paper estimated the energy used along the whole food chain, from making fertiliser to cooking, at about 95 exajoules a year, roughly 30 percent of the world's energy use. Nitrogen fertiliser alone is costly: according to the International Energy Agency, ammonia production accounts for around 2 percent of total final energy consumption, almost all of it from fossil fuels. A farm that depends on this subsidy is not running on its own sunlight.

Techniques that catch more sun and keep it in the land

Behind all of them is a simple aim: more leaves for more months, and everything that grows returned to the soil life rather than burned. Bill Mollison's design method starts with the same questions: where the sun comes from, where the wind blows from and how the slope falls. The cycle graphic above shows which technique works at which station.

Sunlight on leaves. A cover crop and a living mulch keep the ground green through the cool, wet months, when a bare field captures nothing. Polyculture mixes plants of different heights and seasons so that one is growing while another rests. Pioneer plants close a bare surface fastest and make it habitable for what follows.

Plant growth. A food forest and agroforestry stack several layers of leaves above one patch of ground. Syntropic agriculture arranges plants by their light needs and their place in succession and prunes them hard, so that the system keeps producing new growth. Biomass plants are grown only to be cut, and a plant guild groups species so that each fills a gap the others leave.

Roots and fungi. Mycorrhiza receives sugar from the plant and pays for it with water and phosphorus from pores no root can reach. Rhizobia in the root nodules of nitrogen-fixing plants also live on the plant's sugar and use its energy to bind nitrogen from the air. Both are energy from the leaf put to work underground.

Animals. In silvopasture animals graze between trees and turn plants the soil cannot use directly into dung, which feeds the soil life on the spot.

Litter and prunings. Mulch and sheet mulching lay the stored energy of cut plants on the soil surface, where worms and fungi can reach it. In a compost heap the same material is broken down in one place; the warmth in its core is the energy of the plants being released, and what remains feeds the soil life. Green manure grows that food for the soil in one season, and Hügelkultur buries wood that feeds the soil slowly for years.

Soil life. The soil food web is the largest consumer on most land and the engine of the nutrient cycle. Fed well, it builds a stable soil structure with its own sticky by-products.

Humus and char. Humus is energy and carbon held in the soil for years to decades. Biochar keeps part of the carbon of prunings far longer than mulch would, and terra preta shows what centuries of returning ash, charcoal and waste can build.

Heat and cooling. The regreening of dry land turns sunlight that would only heat bare soil back into transpiration, which cools. Nurse trees shade young plants and the ground beneath them. Where heat is welcome, stone does the opposite: a herb spiral stores the warmth of the day and releases it at night, and rock mulch protects the soil where organic cover would burn or blow away.

How it looks at Sa Medada

Sa Medada is a slope in Jerzu, in the Ogliastra on the east side of Sardinia. Sunlight is not what this land lacks. The winters are mild, and the dry season runs roughly from May to September, when the sun is strongest and the rain is absent. In summer the limit on growth is water, not light, which is why the water cycle and the energy flow are hard to separate here. An old olive grove covers part of the land, and maquis grows on the steeper slopes; the LiDAR wetness map shows a comparatively dry main area and moister channels along the edges.

Project Eden therefore starts with pioneer plants, ground cover and water retention. Seen from the energy flow, the aim is that sunlight should fall on leaves rather than on bare earth, and that what grows should stay on the land as food for the soil. A laboratory analysis of the soil does not yet exist, so we make no claims about its humus or its life.

The mild winters allow plants that need a great deal of warmth and light to grow in the open ground, among them banana, mango, avocado, papaya, passion fruit, lychee and moringa. Several fast nitrogen fixers are already in the soil, including Leucaena, Inga edulis, Tephrosia and the coral tree. Plants of this kind are cut back regularly in syntropic systems to feed the soil, and whether that can work on this slope is still open. The service tree, planted in 2024 as the first tree, stands on the very hot southern flank, where the summer sun strikes hardest.