Reading notes from Gaia's Garden by Toby Hemenway
An acre of good pasture soil may support one horse above the ground, and it may contains 8 or 10 horses worth of animals below ground (worms, millipetes, mites etc)
Healty soil and plants are created not by the simple presence of nutrients and soil life, but by the briskness and depths of their flows and interconnections.
Fungi hold a broad spectrum of enzymes able to digest ligning (the tough molecules that makes wood so strong). This gives them a critical niche in the web of the decomposers: without them, the earth might be neck-deep in fallen, undecomposable tree trunks.
The job of worms and mites is to pulverize litter. Their scrurrying and tunneling also mixes the leaf particles with the soil, where the fragments stay moist and palatable for others. The real alchemy- the chemical transformation of the leaf into humus and plant food is done by microorganisms.
Microbes also building up soil. As they feed, certain soil bacteria sectrete gums, waxes and gels that hold tiny particles of earth together. Dividing fungal cells lenghten into long fingers of hyphae that surround crumbs of soil and bind them to each other. These goeey microbial byproducts protect soil from drying and allow it to hold huge volumes of water.
Humus is made of carbon, nitrogen, oxygen and hydrogen, bonded together in ways that makes it difficult for soil organisms to attack.
Of all the ingredients of soil, humus is at far the best at holding moisture, and will absorb four to six times its weight in water.
Humus swells when its wet. As this soil dries, the humus shrinks, leaving air spaces between soil crumbs. This expanding and shrinking process lightens the soil. On humus rich soil, roots and soil organisms can easily tunnel in search of nutrients, and these travels further aerate the soil. Water penetrates the loosened soil deeply, and is stored by humus more longer. Humus alows, moisture and soil-organisms to move deeper into the soil, where thay create more humus, allowing yet deeper penetration, building humus again and so on.
Plant roots secrete very mild acids, which break the bonds that hold nutrients onto the humus. The nutrients are washed into the soil moisture, creating a rich soup. Bathed in this nutricious broth, the plants can absorb as much calcium, ammonium, or other nutrient as they need. When plants have supped long enough, they stop the flow of acid to avoid depleting the humus. This is the direct route plants use, and there is an indirect way in which microbes are the middelmen. In this type of plantfeeding, roots release sugars and vitamins that are ideal food for beneficial bacteria and fungi. These microbes thrive in huge numbers close to roots, lapping up the plant produced food and bathing in the film of moisture that surrounds the roots. In return the microbes produce acids and enzymes that release the humus-bound nutrients, and share this food with the plants.
Its the humus and the life in the soil that keep the earth fertile by holding on to nutrients that would otherwise wash out of the soil into streams, lakes and eventually the ocean.
Plants grown on soil rich in organic matter are more dissease resistant than plants in carbon-poor soil.
A common soil problem is to little nitrogen; ideal is use mulches (organic matter on top of the soil to smother weeds and renew nutrients) and compost with a ratio of 30:1 as decomposer organisms needs a balanced diet, and nitrogen-fixing covercrops
You can use woodshaving or straw on top of the soil ( so as mulch), but not should not be tillted into the soil as it is very poor on nitrogen
Using chemical fertilzers or tilting soil leads to depleting the soil after a few seasons.
The critical elements of a good compost pile are the right ratio of of carbon to nitrogen, optimum moisture and a proper size; -best to mix half brown (dried leaves, woodshavings hay and straw…high in carbon) and half green materials ( kitchen waste, mulch, fresh plant trimmings…high in nitrogin) which will approximate the ideal 30:1 C:N ratio. - save up your materials for a 3 foot ( 90 cm) heap. (only then it can reach the right temp. to kill the seeds of weeds) When building the pile add the materials in layers no more than 6 inches thick. for a small pole just jumble everything together. You can add some soil to the pile.
For quick fertility to soil, use compost. For intnsively worked bedds you can make sheetmulch. But for large areas, for long term fertility, and for shifting the labor to nature ample: use cover crops.
Cover crops are planted to build and hold soil and to smother weeds. They range from long-growing perennials to short-term green manures meant to be slashed in place. (mulch). Their leaves shield to soil from hammering rains and sun, and carpet the carpet the earth in fall with nutritious, humus building litter. Their roots drive deep into the soil, loosening the earth, drawing up nutrients, and placing organic matter than even the deepest plowing. Roots are nature's subtereanean humus builders. Above ground, leaf litter does the job.
Cover crops can serve multiple functions. A blend of 5 to 10 varieties of covercrops sown into the soil can build humus, add nitrogen, mine minerals, bust up heavy soil and attract a wide array of helpfull insects. There are old farm texts that list more then 15 varieteies in their cover crops including 4 grass species, five clovers, plus yarrow, fennel, plantain, dandelion and more…
Roots add organic matter in vast quantities during their constant cycles of growth and decay: plants and their roots don't grow smoothly and continuously, but in spurts. These growth periods are contolled by many overlapping cycles: day/night, wet /dry, cold/warm. Roots in particular are strongly influenced by wet/dry cycles. Aftre a heavy rain, the ground becomes satured with water, and legions of root hair die from lack of oxygen. As the ground begins to dry after a rain, air flows into the now-empty soil pores. Fueled by fresh oxygen and moisture, roots hairs and tips surge into growth, eager extentending towards pockets of nutrients. During this cycle, plants shed huge masses of roots, hourly, daily, constanly - not just in fall when the plants die. This decaying organic matter builds humus deep in the soil, and is one of the benefit of cover crops that can't be achieved in any other way.
Many cover crops send roots 10 to 15 feet deep. (3 - 4,5 m). The more varied covercrops we plant: the more will be the soil life's diversity; this will subdue disease and boost plant growth. (each plant secrets its own array of sugars and other compounds from its roots which attracts differrent communitys of soil organisms to it.
Nitrogen-fixing crops host symbiotic microorganisms that live in nodules among their roots. These bacteria and fungi fix nitrogen gas from the air and exchange their surplus for sugary root secretions.
Both ancient and modern farmers recommend to mulch the nirogin fixing plants before the plants set seeds, because the plants drains nitrogen from stems and leaves at majurity and concentrates in the seeds.
Nitrogen-fixing plants are not only as use until they are used as mulch: when they die they release nitrogen locked in the plants and the microbial nodules. But also during the wet/dry soil cycle there is a constant growth and dieback of roots: the nitrogen plant roots slought off, as do the nitrogen-fixing nodules. Surrounding plants and microbes then absorb these nutrients as the roots and nodules decay.
When building soil or feeding hungry plants, go heavy on nitrogen fixers.
A to rich nitrogen fuel can actually deplete more organic matter than the cover crops adds. So its best to balans out the covercrops of which 10% to 40 % are non nitrogen-fixing plants.
more on specific (nitrogen-fixing) covercrops see edible gardening