Living soil market gardening - Konrad Schreiber . For discussion.

Konrad Schreiber is a french agronomist, and in these 12 videos he's training market gardeners to produce organic vegetables using mulch. Videos in french but try using auto-translated subtitles... my comments and question in italics.

1) Introduction:


How come how plants grow on their own, but the current agricultural techniques have led to a diminishing return?
He will present the current agrological research, developed with farmers in France.

2) Understanding the carbon - nitrogen cycle


The goal - to reach the maximum vegetative yield
Example - goosefoot (weed) will take up available nitrogen (N) from soil and produce carbon (C) (which is exactly the opposite of what agriculture does)
hypothesis: it is carbon that drives plant productivity. It is not soil that is the issue, since plants grow everywhere, but plants are the key. There is a huge variability in plant species, meaning that it is possible to choose adapted plants for whatever growing situation.

Biological succession leads to maximum vegetative yield.
First phase are annuals, that take up the available nitrogen and produce straw = carbon uptake
Next phase are the leguminous pioneer plants, some annual but most perennial. They take up nitrogen from the air to produce more straw = C x10, N +1 (lots more carbon, some nitrogen returned to soil)
Third phase: brambles and pioneer trees
Climax: trees
The system produces more and more carbon (lignin), all without nitrates.
Therefore, it is not N which is the limiting factor, as it is available almost unlimited in the air.
The driving factor is carbon.

How does a tree grow? Breathes N, "execretes" C in the form of lignin in the trunk. Leaves = 50% cellulose, 50% lignin which is almost exactly the composition of ramial wood chips (RWC)

cellulose = "fast carbs" , more nitrogen, carbon stable
lignin = "slow carbs" , less nitrogen, lots more carbon. Lignin is an interesting food source because every C-C link releases energy when its broken. Cellulose to start the engine, lignin to keep it going.

Living beings breathe, eat, digest, and defecate in one form or another. Human beings eat carbon and therefore you will find carbon in their digestion and defecation. We inhale O2 and exhale CO2, but also a whole lot of N (80% of air), which is why we find nitrogen in the execretions. We live of nitrogen.
This is not true of animals - N is in what they eat! He clearly understands plants, but not humans... his examples are therefore incorrect, but his arguments as far as plants are concerned is interesting.
He then argues that the essential ingredient is carbon, because nitrogen is available in the air.
He tells of his experiments with RWC, things were growing, but they could not find nitrates in the soil to explain the growth.

Consider soil as an organism, that breathes N, eats C, digests C and NH3, excretes C and N. Therefore the soil of your field needs to breathe, and eat C, so that the result is a soil with more N. In order to increase soil nitrogen, it is necessary to add carbon.

1) soil needs to breathe - Aerobic
2) who eats in the soil? - Biological activity
3) food - lignin. They typically use 20 - 25t of straw/ha sometimes more. Could I use less of a different material higher in lignin?

Generally, a market gardener is not limited in the lignin source, as it is a smaller surface. Can be easily imported, for example from landscape gardeners. The issue is more tricky for large scale farming. But to rely less on outside inputs, green manures can help: plants with a high lignin content that grow quickly. Sorghum, corn in summer, cowpeas, ancient cereals, mustard, rape in winter. The goal is to produce "straw"

---  I will continue the summary at a later date.

Resume continued.

Ragweed

for ex. is a problematic weed, what does it do? It produces lignin. So to get rid of it, add carbon to the soil.

Goosefoot, amaranth weeds

= replace with quinoa or edible amaranth. Sell the grain, keep the plant.

maize

- produces a huge amount of biomass in a short time

Sorghum

- great if your soil is warm enough

maizewill produce approx. above ground, 60% of which is in the grain, 40% in the stalk. But below ground, 50%of the above ground biomass, half roots, half exudates. So if I have a yield of 10t of grain, I'll have about 7t of stalk, but also about 8 t below ground biomass.

When calculating biomass produced, always count both above and below ground yield. What counts is the amount of biomass left in the field. He then advocates using organic fertiliser to maximise the production of biomass left in the field.

However, with a radish, practically all biomass is removed. With most vegetable crops, most of biomass is removed: therefore use cover crops or intercropping to fill the void, or import biomass from elsewhere.
Example: Three sisters (Milpa). maize produces lots of lignin, harvest of flour = slow carbs, beans are stand-alone as to N (doesn't need any added to grow, but doesn't give any to the corn either, only after it is dead), harvest yields protein, squash   soak up the sun by covering the ground, yields fast carbs in the flesh plus fat in the seeds. Its a useful model combining a stalk, a climber and a ground cover.

Hence it is important to find the useful pairs of plants that go well together: look at companion practices in gardening, especially as far as feeding the soil is concerned. Look for complementary plants that don't compete.
ex. grasses and legumes (lucerne/white clover/violet clover and wheat; italian ray grass and soy, agrostis and soy), brassicas and legumes (rape and vetch), grasses and grasses (brachiaria=signal grass and maize but we haven't been able to do this in France). In a garden setting, this is done with cover cropping, for ex. hoeing the clover before planting cabbage - alternating the partners

To make this work with both partners staying alive, you need to understand the life cycles of your tandem partners. Ex. Ray grass has three periods of seed setting: april, end may, beginning july (observation of cattle farmers in the region). The last cut will have a low yield, seeds will set quickly, with small seedheads = low competition for my soy.  Cut the raygrass and leave in place once in April when its starting to make seedhead, three weeks later the raygrass is making another seedhead, sow the soy into the standing grass, cut and leave the raygrass on top. Therefore sow the soy mid-may into the raygrass. Raygrass acts as a living mulch and outcompetes weeds. At harvest, the raygrass stays alive, and the cycle starts again without having to reseed the grass.

Sunflowers and fenugreek are good partners. Also agrostis and soy (agrostis needs cutting only once )

Anybody tried this?

He refers to the cold composting technique of Walter Witte in this short clip.

The carbon-nitrogen cycle is driven by carbon. Usually its nitrogen that is the limiting factor for plant production.
In a field of cereals, or a forest, where does the nitrogen come from? - in the first case, perhaps some legumes but not in the second case: Most comes from the air.
In a natural ecosystem,

10% of N comes from the air,

60% from nitrogen fixers,

30% from biodegredation

The nitrogen cycle is correlated to 90% to the carbon cycle.
The driving factor is carbon.
Degradation cycle, carbon-nitrogen ratios:

organic matter: C/N 150 to 50

ideal bacterial food, C/N=24

bacteria mineralise at C/N=8, plant food

The first stage of degradation needs aerobic conditions which generates more nitrogen: aerobic bacteria create a sort of "soup" from the organic matter which is absorbed by earth worms.
In the second stage about 3x reduction of carbon released by soil organisms as CO2, making the second stage a concentration of nitrogen. The area close to living soil is richer in Co2 than higher up, helping plants to grow, especially as the mulch traps the CO2.
To be self-sufficient in nitrogen

organic matter on top of the soil

maximum microbiological activity

C/N of mulch as high as possible

In this line of argument, the best mulch material is actually heart wood! What are your opinions on this?

Calculation exercise.
To change C/N=150/1 to 25/1: 6xN
1t straw = 1t dry material = 0.4t C average at C/N=150, therefore 2.7 N units
at second stage, degradation, 0.4t C at C/N=25 therefore 16 N units
Therefore the pre-digestion of straw pulls about 13 N units from air
To simplify, the C/N of mulch material is approx. 10x the N gained in fertility.
The lack of C in green manure means it doesn't do much for fertilisation.
25t of straw = 400 N units, but half of which is used in mineralisation. We're left with 200N for fertility. Of the 25t of straw,2t ends up as soil carbonisation.
K2=1% without any tillage, up to 5% with intensive tillage
Starting with 2% soil organic matter, 1000m2=1ha, 30cm of arable soil depth: 3000m3=4000t/ha approx. soil mass.
resulting in 80t soil organic matter at 58%C, approx 40t C, C/N=10: 4t of N. At K2=1%, this produces 40 N units, which isn't much.


Same calculation with 5% organic matter, yields 100 N units: So the higher the organic matter content the better

However, if the organic matter is tilled in, the N taken from air in the degradation stage is not available: "faim d'azote"= nitrogen deficiency
Sometimes in order to rapidly increase soil organic matter, organic matter is tilled in once, risking nitrogen deficiency. After that, no more tilling.

Susan Wakeman wrote:
He refers to the cold composting technique of Walter Witte in this short clip.

I found some more info on this and made it available here: Walter Witte composting thread

thank you for posting this information