Biomass and material

Where the cycle breaks in ordinary land use

In much of today's land use, material moves in one direction only: off the land. The cycle breaks at four points.

Burning prunings. Pruning residues from orchards are often burned at the field edge; in southern Italy this is still common practice in olive groves. The amounts are considerable. Across Mediterranean olive groves, annual pruning yields an average of 1.31 tonnes of dry residue per hectare, pruning every second year 3.02 tonnes. Burning sends the carbon and much of the nitrogen into the air, and every open fire is a risk in dry country.

Tidying and carting away. Raked leaves, mown grass, cleared deadwood and hedge cuttings often leave the land as green waste. What looks tidy is soil cover and soil food that the land then lacks.

Harvest without return. Fruit, wood and fodder leave the land, and with them carbon and nutrients. When the residues of the kitchen and processing do not come back, the loss becomes permanent. According to UNEP, around 1.05 billion tonnes of food were wasted worldwide in 2022, almost a fifth of what was available to consumers.

Bare soil. Where nothing covers the ground, the next heavy rain carries off soil and its organic matter. How much cover matters was shown by rainfall simulations in Spanish olive groves: compared with tilled ground, plots covered with spontaneous vegetation, pruning residue or both lost more than 95 percent less soil and more than 85 percent less organic carbon.

The gap is then filled from outside, with bought fertiliser, peat, bagged substrate and imported mulch. The land becomes dependent on supply instead of feeding itself.

Techniques that close the cycle

The aim is simple to state: whatever the land grows stays on the land, or comes back to it. Each station of the loop has its own techniques.

Growing more material. Biomass plants are grown above all for their cuttings and can be pruned again and again. Nitrogen-fixing plants grow fast even on poor soil and leave behind leaves rich in nitrogen. Pioneer plants and nurse trees produce material where nothing else grows yet, and a food forest or polyculture uses several layers and seasons. Fast-growing species, including some regarded as invasive elsewhere, are nature's own strategy for covering bare ground quickly, and they hold great potential for rapid renaturation. Terra Humana never uses species on the EU list of invasive alien species of Union concern.

Cutting and dropping. In syntropic agriculture, regular pruning is the engine of the system: the cut material is laid at the foot of the trees as mulch, and the pruning spurs new growth. A dynamic accumulator draws minerals from the subsoil and returns them to the surface with its leaves. Green manure is sown so that it can be cut at flowering and left on the ground. In a Mediterranean climate, the heavy cutting belongs to winter and spring; in summer, shade is worth more than mulch.

Harvest with return. Agroforestry produces fruit, wood and fodder on the same ground, so more of the material stays in the system. In silvopasture, animals turn grass and leaves into dung that falls back onto the pasture. A plant guild groups plants so that one feeds the other. Compost brings kitchen scraps, peels and pomace back to the land, and a composting toilet can do the same for human excreta.

Covering the soil. Mulch is the central station of the loop: this is where cut material does its first work, as shade, protection from erosion and food for soil life. Sheet mulching builds new beds from layers of organic material. Living mulch and cover crops keep the ground covered while they grow and leave straw behind in summer.

Letting it decay. The soil food web turns dead material into plant food, and mycorrhiza carries nutrients back to the roots. In a compost heap the same breakdown happens on purpose and faster. Hügelkultur puts thick wood to use, which decays slowly in the ground and holds water like a sponge.

Storing for the long term. Material that passes through soil life becomes humus in part. Wood that is too coarse for mulch can be turned into biochar instead of smoke, a form of carbon that stays in the soil for centuries. The terra preta of the Amazon shows what households can build over generations from charcoal, ash, bones and kitchen waste.

The material cycle at Sa Medada

Sa Medada lies on a slope at Jerzu in Ogliastra, on the east side of Sardinia, with a dry summer from about May to September and mild winters. The land is an old olive grove, with macchia on the steeper slopes. Both produce material: olive wood and leaves, and the shrubs of the macchia.

The LiDAR wetness map shows a comparatively dry main area and moister channels along the edges. On the dry main area, little new material grows in summer, and what lies on the ground decays slowly. That is why soil cover is so valuable here: every bit of shade lowers the heat on the soil.

Project Eden begins with pioneer plants, soil cover and holding water. Its aim is for the land to produce its own mulch rather than import it. Several plants growing in the ground could become suppliers: the nitrogen fixers tephrosia, the coral tree, Inga edulis, pacay and leucaena, which agroforestry elsewhere uses as suppliers of green material, alongside fruit plants such as bananas and papaya, whose large leaves make soil cover. Which plants actually deliver how much material on this site has yet to be seen. There is no laboratory analysis of the soil yet; it will one day show whether the returned material is building humus.