It is a common misconception that biomass in the soil is not essential for growth,
but that is simply untrue.Soil carbon is literally a combination of a soil conditioner (keeps soils together, keeps wind from blowing soil, keeps clays from forming thick crusty flakes, etc) as well a medium through which organic acids produced by microbes, soil fungi, and even plant roots, are able to slowly attack, break down, and dissolve inorganic nutrient supplies found in clays and crushed rock mineral sources. Without the biomass, the plant is significantly impacted in its ability to absorb these nutrients, and any dissolved nutrients are EASILY washed out. Only very simple "plant like" species, like mosses and lichens, can live without an existing biomass component to their substrate. Soil building over the aeons requires first going through this "lichen" period, so that dead and dried out lichens slowly accumulate in the environment, and act like sponges while decomposers saturate them with organic acids, and liberate mineral sources for actual plants. After that, the process slows down, and depending on the climate, a specific biome will take root, which ultimately determines what the character of the soil will be like.
This is why pouring water on the carbon-less sahara desert will not magically transform it into a lush paradise. It will just wash out all the dried out mineral precipitates between the sand grains, and make the desert even less hospitable to life. The sahara used to be a fertile grassland, before climactic shifts caused it to dry out, and natural aerobic decay of the biomass by microbes depleted the blowing topsoil, slowly transforming it into little more than blowing sands.
Excessive qualtities of carbon sponge in the soil cause serious problems for most ecosystems, because it holds excessive water, and becomes swampy, and anaerobic decay processes take over. Root systems need oxygen to thrive, so the anaerobic conditions actively suffocate plants, making the area into a disgusting bog of slowly rotting vegetation. The biomass holds on to the acids produced by this decay, making the soil very inhospitable, even after being drained.
The process of composting (for a garden), takes a nitrogen rich source, like kitchen scraps, bird or animal dung, fish emulsion, etc--- and blends it with a carbon rich source, like dry leaves, grass straw, or bast fiber heavy plant stalks. A good deal of this nitrogen gets blown off as nitrogen gas as microbial activity uses it to break down the cellulose and lignins in the plant matter, but enough of it stays as free nitrate ions, that it chemically binds to the compost's matrix, and fixates it against being washed away. This process is very similar to
mordanting cellulose fibers, before dying them. The nitrogen becomes chemically bound to the compost, and also buffered by all the inorganic cations it soaks up while being made. Compost is the perfect fertilizer, because it contains literally everything the plant needs, and releases it only as the plant requires.
Raw animal dungs, on the other hand, deliver a whole lot of nitrogen all at once in a soluble form. This is why they are "hot"-- Urea is very reactive biologically, and it basically causes chemical burns to the plant's leaves, stems, and roots--- Without biomass in the soil to catch the urea, and hold on to it for slow re-release, the nitrogen then just washes out the next time it rains. One solution to this problem, is to produce
"Manure tea". This is basically just pouring water through scooped up poop, and letting all the nitrates leech into the solution, then conspicuously applying it as a nitrogen booster through irrigation. Over application will nuke the plants though. Once the dookie has been used to make manure tea, and stops colorizing the water, it is safe to apply as a mulch. This is frequently done by people who want to use manure fertilizers, but dont want to go through the effort of composting it first. One of the benefits of manure tea over other methods is that more of the nitrogen ends up in plants, as opposed to composting. The leeched poop left over from the manure tea will naturally turn into compost over time, as new manure tea is added.
Kohaku mentioned using mushroom compost as a possible fertilizer. Mushroom compost is just ordinary compost, that has had mushrooms grown on it until the spawn died out from starvation. Mushroom compost therefore, has all the cations and nitrogen compounds normally found in healthy fresh compost stripped out of it, by the biologicial activities of the mushroom. The positive side of mushroom compost, is that it often is mixed with casing clay, due to the reproductive cycle of crimini (white button) mushrooms; The mushrooms are light induced. That is to say, they start producing mushroom caps, instead of threadlike mycelial fibrils, after those fibrils are exposed to light and air. To ensure good colonization of the compost for the mushroom crop, the mushroom farmer 'cases' the compost in a layer of organic free clay, which keeps light and air out. When the mycelial fibrils have fully permeated the compost, the farmer will purposefully disturb the surface of the casing clay, which exposes the mycelium to air and light--initiating fruiting. This will be repeated as often as needed, until the compost gives out, and the mycelium can no longer fruit. After this point, the compost is heated to sterilize it, and tumbled together. The admixture of this clay, coupled with the enzymes present in the mycelium, causes partial decomposition of the clay on a chemical level, making it receptive to breakdown by the microorganisms found in healthy soil and the acids produced by plant roots. Mushroom compost is therefore more nutritious to soil than raw organic material, like
coir or dry straw, but only marginally so. Mushroom compost, like coir, suffers a profound nitrogen deficit, and will rob nitrogen compounds from the soil it is mixed into through osmosis. Mushroom compost and coir, must therefor be used with manure tea, or with commercial fertilizers, or they will actually inhibit plant growth. This is a common problem with novice gardeners who mulch with dry leaves, or bales of dry wheat straw. They forget to supply a nitrogen source with the watering can, and the mulch literally robs the soil blind, making their plants grow poorly.
As for the issue with limits on how much a plant can take from the soil per season, you clearly have no concept of how ravenous some cash crops are, like corn or cotton. You can take a rich field from productive to barren in just 10 years growing intensive cotton on it, with just one crop per year!
Cotton is a "Only once in a while" crop. Not an 'All the time!' crop. Many economists are unable to comprehend this fact, along with many urban dwellers. (Not to sound offensive.) It and corn are notoriously deleterious to soil, which is why corn ethanol is not a viable alternative energy source.
This deleterious behavior toward soil is WHY it is a cash crop to begin with-- It has natural scarcity built right in, because it is so damned abusive to soil, that you just cant grow lots and lots of it.
The basic rule of thumb, is that the more you have to till and preen the soil while the crop is on it, the more destructive to the soil it is. This is why corn is so destructive. It isnt necessarily that the corn plant is hungry, (though cotton most assuredly is!) so much as it is that exposure of the soil to sunlight and air causes aerobic decomposition of the soil's biomass, and the heavy water requirements of the crop itself cause excessive soil mineral leeching. Combined, the soil is left abused after a corn planting, and in serious need of replenishment.
Some mitigating approaches to crop cultivation is to plant 2 or more crops simultaneously, with one being the primary food crop, and the others being used as a ground cover, and after harvest, as a
green manure; (Such as clover planted beside beets, turnips, or potatoes) Another is to grow the cover plant and the food crop, then after harvesting the food crop, use the cover crop as a graze for animal pasturage. You dont really care if the cover crop gets harmed by the hot animal manure-- it's just a cover crop.
Examples of this include growing a root vegetable next to a lowlying ground cover, like clover-- or growing clover next to a short season grain crop, like buckwheat, in the spring and fall.
These approaches keep the soil shaded, and covered, which prevents aerobic destruction of the biomass in the soil, and retaining soil vitality.
Other practices are things like crop rotation, where you will grow a high maintenance crop, like corn or cotton one year, grow a soil cover and vegetable crop the next with a winter green manure, then allow the field to lie fallow with tall grass before tilling it under in fall of the third year, before returning to the high maintenance crop on the fourth year.
If you have 3 plots, you can have each one of them offset on the stage of the rotation cycle, and have concurrent crops every year, at lower but sustainable yeilds.
Essentially, retaining soil carbon, and keeping it loaded with inorganic cations like calcium, phosphorus, potassium and pals, is the quintessential purpose of soil management, which makes carbon the fundamental variable in soil culture. That's why I used it as the simplified nutrient in the simplified model I demoed.
Most of the others can actually be implied to be present, if you use compost as the primary fertilizer.
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Topic: Improved Farming, Rebooted: Agricultural Revolution (Read 148856 times)