Soil

Every farm is a bank, and the soil is the capital in it. Spend the interest and the account holds. Break into the principle and it runs down. The industrial habit treats soil as a stand for roots, inert until a bag is poured on it. A farm feeding its own household cannot afford that habit: the bag is an open line to somebody else's factory.

Texture is fixed, structure is yours

Texture is the mineral skeleton: the share of sand, silt and clay, fixed by the rock and the water that laid it down. No amount of work changes it. Structure is how those particles glue into crumbs, and structure does respond to management. Good structure holds water like a sponge, holds air like a lung, and lets a root push through wet ground without tearing. Columella's test is the oldest one still in use, and it costs nothing.

Compaction is the quiet killer

Compaction is structure destroyed. Weight squeezes the pore space out, water runs off instead of down, roots meet a plate they cannot cross, and the biology that needs air goes dormant. On dozer-shaped ground the fill can be compacted subsoil at half a percent organic matter, while the slope holds eight to eleven centimetres of topsoil. Those numbers decide what gets planted where. Break the plate with a broadfork and keep wheels and stock off wet ground.

The biology, and the nitrogen it releases

A living soil is a food web: bacteria, fungi, protozoa, nematodes, arthropods, earthworms. Mycorrhizal fungi trade water and minerals to the plant for sugars the plant made. Bacteria mineralize organic matter and release the nitrogen locked in it, and that release feeds the crop. Bowles and co-workers showed in a 2015 PLOS ONE study that soil organic matter supplies that nitrogen in organic systems, with reduced losses when the cycle is tight. Marschner's Mineral Nutrition of Higher Plants covers what each mineral does inside the plant.

Legumes fix nitrogen from the air, and the ancient writers saw the effect without knowing the cause.

Cato's rule is blunter. "Lupines, field beans and vetch manure corn land." The catch is in the keeping. Fixed nitrogen is real, but residue left to rot cold on the surface loses a third to nearly half of its ammonia to the air, and a green manure that never reaches the root zone is a bill paid twice.

Minerals, pH and the limits

Deep-rooted plants lift minerals from the subsoil and drop them at the surface. It is only a lift, though. The root draws on a finite vault, so on a hard boundary the column is pumped downward while the harvest keeps taking from the top. Plants cannot make phosphorus and calcium out of air the way legumes make nitrogen, so something has to bring new mineral in, and on a closed farm that is the animal, the tree, or rest.

pH gates the same system. West Virginia's median topsoil pH is 5.0, with forty-four percent of the state below pH 5. Rhizobia nodulate above pH 5 and will not survive below it, which turns a one-time inoculant purchase into an annual one. Lime is the cheapest correction on the list, and its rate comes from a soil test.

Building fertility with nothing from the store

Four inputs, all already on the farm. Rotate a legume through the ground and let it fix. Return the manure, covered, so sun and rain do not strip it. Compost every scrap that is not eaten. Pliny described marl acting "as a fat in relation to the earth," and recorded one dressing fertilizing for fifty years, white chalk in Britain for eighty. Varro shaded the manure pit with leaves and branches, "for the sun draws out from the manure those elements which the land requires."